remove logs

.gitignore

@@ -5,3 +5,6 @@ compile_commands.json
 .vscode/c_cpp_properties.json
 .vscode/launch.json
 .vscode/ipch
+
+
+scripts/__pycache__/

README.md

@@ -82,20 +82,28 @@ Verify access: `test -w /dev/ttyUSB0 && echo ok`
 
 1. Flash firmware and open the serial monitor at 115200 baud.
 2. Confirm `TCA9548A detected` and four valid sensor channels (`ch2`–`ch5`).
-3. Run PID autotune once per physical unit (values are stored in EEPROM):
+3. Find **stir fan** speed (optional — default is **PWM 178**, ~70%):
 
    ```
    target 0
-   autotune 45
+   fanchars
    ```
 
-4. Start drying:
+   Sweeps **30%, 100%, 60%, 80%** fan — heats to max **60°C** corner at **100%** heater. Cools to **40°C** avg between runs. Skips a fan speed if 60°C isn't reached in time. Optional midpoint refine if best isn't at 30% or 100%. Or: `python3 scripts/fan_characterize.py`. When done, `fanchars save` writes the winner to EEPROM (or skip and keep the 178 default).
+
+4. Tune **heat PI** (stored in EEPROM on autotune complete):
 
    ```
-   target 55
+   target 0
+   pid default
+   autotune 50
    ```
 
-Send `help` over serial for all commands (`target`, `fan on/off`, `log on/off`, `status`, `pid`, etc.).
+   Cutoff follows target (`target + 12°C`, max 95°C) — e.g. ABS at 55°C trips at 67°C corner, nylon at 80°C at 92°C.
+
+5. Dry at your target — fan runs at stir PWM (default **178**) whenever target > 0, including heat-up. Override with `fan <pwm>`; `fan auto` returns to default. Fan auto-off below 40°C applies only in idle (`target 0`).
+
+Send `help` over serial for all commands (`target`, `fanchars`, `fan`, `log on/off`, `status`, `pid`, etc.).
 
 ## Raspberry Pi control
 

include/config.h

@@ -12,6 +12,10 @@ static const uint8_t SENSOR_COUNT = sizeof(SENSOR_CHANNELS) / sizeof(SENSOR_CHAN
 // SHT31 I2C address (ADDR pin low → 0x44, high → 0x45)
 static const uint8_t SHT31_ADDRESS = 0x44;
 
+// Bus timeout (Wire.setWireTimeout) — bounds a stuck I2C transaction so a
+// glitch resets the TWI hardware instead of hanging the whole sketch.
+static const uint32_t I2C_TIMEOUT_US = 25000UL;
+
 // ---------------------------------------------------------------------------
 // Outputs — D5 has hardware PWM; heater on A2 uses burst control (SSR-friendly)
 // ---------------------------------------------------------------------------
@@ -21,67 +25,81 @@ static const uint8_t HEATER_PIN = A2;  // heater via solid-state relay
 // ---------------------------------------------------------------------------
 // Temperature control
 // ---------------------------------------------------------------------------
-static const float TARGET_TEMP_C = 0.0f; // power-on default: idle (heater off)
-static const float AUTOTUNE_DEFAULT_TEMP_C = 40.0f; // autotune when no temp given and idle
-static const float TARGET_MIN_C = 0.0f;   // 0 = idle (heater off, fan at idle speed)
+static const float TARGET_TEMP_C = 0.0f;
+static const float AUTOTUNE_DEFAULT_TEMP_C = 40.0f;
+static const float TARGET_MIN_C = 0.0f;
 static const float TARGET_MAX_C = 80.0f;
-static const float OVERTEMP_FRACTION = 0.05f; // hard cutoff at target * 1.05
+// Hard ceiling (sensor / enclosure limit). Cutoff when regulating = target + CUTOFF_ABOVE_TARGET_C.
+static const float EMERGENCY_ABSOLUTE_MAX_C = 95.0f;
+static const float CUTOFF_ABOVE_TARGET_C = 12.0f;
+static const float CUTOFF_RECOVERY_BAND_C = 5.0f;
+static const float CORNER_STOP_MARGIN_C = 5.0f;
 
-// PID on chamber average
-static const float PID_KP = 4.0f;
-static const float PID_KI = 0.05f;
-static const float PID_KD = 6.0f;
+inline float emergencyCutoffForTarget(float targetC) {
+  if (targetC <= 0.0f) {
+    return EMERGENCY_ABSOLUTE_MAX_C;
+  }
+  float cutoff = targetC + CUTOFF_ABOVE_TARGET_C;
+  if (cutoff > EMERGENCY_ABSOLUTE_MAX_C) {
+    cutoff = EMERGENCY_ABSOLUTE_MAX_C;
+  }
+  return cutoff;
+}
 
-// Tiered heater cap — more power when cold, gentle near setpoint
-static const float HEATER_MAX_DUTY_COLD = 85.0f;  // avg >=10 °C below target
-static const float HEATER_MAX_DUTY_MID = 65.0f;   // avg 3–10 °C below target
-static const float HEATER_MAX_DUTY_NEAR = 45.0f;  // avg <3 °C below target
-static const float HEATER_COLD_BELOW_C = 10.0f;
-static const float HEATER_WARM_BELOW_C = 3.0f;
-// Below this band from target, only the hard cutoff limits max-corner (full heat-up)
-static const float CORNER_LIMIT_BAND_C = 10.0f;
+// Heat PI on average temp (no D term)
+static const float HEAT_PI_KP = 4.0f;
+static const float HEAT_PI_KI = 0.05f;
 
-// Ramp-up limit (% per second) — still caps sudden jumps
-static const float HEATER_SLEW_UP_PER_S = 18.0f;
+// Fixed circulation fan (~70%, fanchars winner); override with "fan <pwm>" when regulating
+static const uint8_t FAN_STIR_PWM = 178;
 
-// Hot-corner limiter: taper heater as max corner approaches stop temperature
-static const float MAX_TEMP_HEADROOM_C = 15.0f;
-
-// Average-temp approach: taper only in the last few °C before setpoint
-static const float APPROACH_BAND_C = 4.0f;
-
-// When spread is good, allow hottest corner slightly above target so avg can reach setpoint
+// Legacy aliases for autotuner relay math only
+static const float PID_KP = HEAT_PI_KP;
+static const float PID_KI = HEAT_PI_KI;
+static const float PID_KD = 0.0f;
 static const float GOOD_SPREAD_C = 5.0f;
-static const float BALANCED_MAX_ABOVE_TARGET_C = 2.0f;
-static const float SPREAD_HEADROOM_FACTOR = 0.5f; // extra max-corner °C per °C of spread
+
+// Corner taper when avg is near target — keeps hottest sensor below emergency
+static const float CORNER_LIMIT_BAND_C = 2.0f;
+static const float MAX_TEMP_HEADROOM_C = 15.0f;
 
 static const uint16_t HEATER_CYCLE_MS = 3000;
 
-// Fan PWM (0–255)
-static const uint8_t FAN_IDLE_PWM = 77;   // ~30 % — optional override via "fan on"
-static const float IDLE_AUTO_FAN_OFF_TEMP_C = 40.0f; // idle: fans off when max corner below this
-static const uint8_t FAN_MIX_MIN_PWM = 70;    // ~27 % — light mixing when spread rises
-static const uint8_t FAN_HEAT_MIN_PWM = 100;  // ~39 % — floor while heating (near setpoint)
-static const uint8_t FAN_HEAT_MAX_PWM = 140;  // ~55 % — cap during heat-up
-static const float FAN_OFF_BELOW_TARGET_C = 8.0f; // no heat-up fan when avg this far below target
-static const float FAN_RAMP_BELOW_TARGET_C = 15.0f; // fan ramps in between this and FAN_OFF_BELOW
-static const uint8_t FAN_MIX_MAX_PWM = 200;   // ~78 % — cap for spread-driven mixing
-static const uint8_t FAN_MAX_PWM = 255;       // failsafe / over-temp only
+// Fan PWM — stir speed when target > 0; off below 40°C only when idle (target 0)
+static const uint8_t FAN_IDLE_PWM = 77;
+static const float IDLE_AUTO_FAN_OFF_TEMP_C = 40.0f;
+static const uint8_t FAN_MAX_PWM = 255;
+static const bool FAN_PWM_INVERT = true;
 
-// Corner mixing — moderate airflow; full speed reserved for safety
-static const float SPREAD_DEADBAND_C = 0.5f;
-static const float SPREAD_FULL_MIX_C = 8.0f;
 static const float SPREAD_EMA_ALPHA = 0.45f;
 
-// PID auto-tune (relay method) — run with: autotune 45
+// PID auto-tune (relay method) — heat PI only
 static const float AUTOTUNE_HYSTERESIS_C = 0.4f;
-static const float AUTOTUNE_PREHEAT_BAND_C = 5.0f;
+static const float AUTOTUNE_PREHEAT_BAND_C = 3.0f;
 static const float AUTOTUNE_PREHEAT_DUTY = 100.0f;
-static const uint8_t AUTOTUNE_PREHEAT_FAN_PWM = 70; // low fan for entire autotune
-static const uint8_t AUTOTUNE_CYCLES_REQUIRED = 6;
-static const uint32_t AUTOTUNE_PREHEAT_TIMEOUT_MS = 1200000UL;  // 20 min
-static const uint32_t AUTOTUNE_SESSION_TIMEOUT_MS = 3600000UL;    // 60 min total
-static const uint32_t AUTOTUNE_RELAY_PERIOD_MAX_MS = 2400000UL;   // count periods up to 40 min
+static const uint8_t AUTOTUNE_PREHEAT_FAN_PWM = 0;
+static const uint8_t AUTOTUNE_CYCLES_REQUIRED = 5;
+static const uint32_t AUTOTUNE_PREHEAT_TIMEOUT_MS = 1200000UL;
+static const uint32_t AUTOTUNE_RELAY_STALL_MS = 1500000UL;
+static const uint32_t AUTOTUNE_SESSION_TIMEOUT_MS = 3600000UL;
+static const uint32_t AUTOTUNE_RELAY_PERIOD_MAX_MS = 2400000UL;
+
+// Fan characterize — fixed heater, sweep fan PWMs, pick lowest spread
+static const float FANCHARS_MAX_CORNER_C = 60.0f;
+static const float FANCHARS_COOL_AVG_C = 40.0f;
+static const float FANCHARS_PRECOOL_MARGIN_C = 2.0f;
+static const float FANCHARS_HEATER_PCT = 100.0f;
+// Coarse sweep order: 30%, 100%, 60%, 80% fan
+static const uint8_t FANCHARS_COARSE_PWM[] = {77, 255, 153, 204};
+static const uint8_t FANCHARS_COARSE_COUNT =
+    sizeof(FANCHARS_COARSE_PWM) / sizeof(FANCHARS_COARSE_PWM[0]);
+static const uint8_t FANCHARS_LIMIT_LOW_PWM = 77;
+static const uint8_t FANCHARS_LIMIT_HIGH_PWM = 255;
+static const uint8_t FANCHARS_MAX_RESULTS = FANCHARS_COARSE_COUNT + 1;
+static const uint32_t FANCHARS_HOLD_MS = 60000UL;
+static const uint32_t FANCHARS_HEAT_TIMEOUT_MS = 2700000UL;
+static const uint32_t FANCHARS_COOLDOWN_TIMEOUT_MS = 2700000UL;
+static const uint32_t FANCHARS_LOG_INTERVAL_MS = 1000UL;
 
 // ---------------------------------------------------------------------------
 // Timing
@@ -89,4 +107,4 @@ static const uint32_t AUTOTUNE_RELAY_PERIOD_MAX_MS = 2400000UL;   // count perio
 static const uint32_t SENSOR_READ_INTERVAL_MS = 1000;
 static const uint32_t CONTROL_INTERVAL_MS = 500;
 static const uint32_t SERIAL_REPORT_INTERVAL_MS = 2000;
-static const bool LOG_CSV_DEFAULT = false; // enable with serial command: log on
+static const bool LOG_CSV_DEFAULT = false;

include/fan_characterize.h

@@ -0,0 +1,75 @@
+#pragma once
+
+#include <Arduino.h>
+
+#include "config.h"
+
+class FanCharacterize {
+public:
+  enum class Phase : uint8_t { Idle, Precool, Heat, Hold, Cooldown, Done, Failed };
+
+  FanCharacterize();
+
+  Phase phase() const { return phase_; }
+
+  bool isActive() const;
+
+  uint32_t elapsedMs(uint32_t nowMs) const;
+
+  uint8_t profileIndex() const { return profileIndex_; }
+
+  uint8_t profileCount() const { return FANCHARS_COARSE_COUNT + 1; }
+
+  uint8_t currentFanPwm() const;
+
+  float heaterPct() const { return heaterPct_; }
+
+  uint8_t winnerFanPwm() const { return winnerFanPwm_; }
+
+  bool isRefineRun() const { return refineRun_ && profileIndex_ >= FANCHARS_COARSE_COUNT; }
+
+  const char *phaseName() const;
+
+  bool start(float maxCornerC, float avgTempC);
+
+  void abort();
+
+  void reset();
+
+  bool update(float avgTempC, float maxTempC, float spreadC, uint32_t nowMs, float &heaterDutyOut,
+              uint8_t &fanPwmOut);
+
+  void logIfDue(const float *sensorTemps, const bool *sensorValid, uint8_t sensorCount,
+                float avgTempC, float minTempC, float maxTempC, float spreadC, uint32_t nowMs);
+
+private:
+  struct ProfileResult {
+    uint8_t fanPwm;
+    float meanSpreadC;
+  };
+
+  void resetProfileStats();
+  void beginProfileHeat(uint32_t nowMs);
+  void enterHold(uint32_t nowMs);
+  void finishProfile(uint32_t nowMs);
+  void skipProfile(uint32_t nowMs, float maxTempC);
+  void planRefine(uint32_t nowMs);
+  void finishAll(uint32_t nowMs);
+  void fail(const __FlashStringHelper *reason);
+
+  Phase phase_;
+  float maxCornerC_;
+  float coolAvgC_;
+  float heaterPct_;
+  uint8_t profileIndex_;
+  uint8_t refineFanPwm_;
+  bool refineRun_;
+  uint32_t sessionStartMs_;
+  uint32_t phaseStartMs_;
+  uint32_t lastLogMs_;
+  float spreadSum_;
+  uint16_t spreadSamples_;
+  uint8_t resultCount_;
+  uint8_t winnerFanPwm_;
+  ProfileResult results_[FANCHARS_MAX_RESULTS];
+};

include/pid_autotuner.h

@@ -24,12 +24,11 @@ public:
         spreadSamples_(0),
         cycleCount_(0),
         aboveSetpoint_(false),
+        useMaxSensorPv_(false),
         sessionStartMs_(0),
         phaseStartMs_(0),
-        resultKp_(PID_KP),
-        resultKi_(PID_KI),
-        resultKd_(PID_KD),
-        resultFanMixMax_(FAN_MIX_MAX_PWM) {}
+        resultKp_(HEAT_PI_KP),
+        resultKi_(HEAT_PI_KI) {}
 
   Phase phase() const { return phase_; }
 
@@ -47,12 +46,14 @@ public:
 
   float preheatTargetC() const { return setpointC_ - AUTOTUNE_PREHEAT_BAND_C; }
 
+  bool usesMaxSensor() const { return useMaxSensorPv_; }
+
   const char *phaseName() const {
     switch (phase_) {
     case Phase::Preheat:
       return "preheat";
     case Phase::Relay:
-      return "relay";
+      return useMaxSensorPv_ ? "relay-max" : "relay-avg";
     default:
       return "";
     }
@@ -74,7 +75,7 @@ public:
     Serial.print(preheatTargetC(), 1);
     Serial.print(F("-"));
     Serial.print(setpointC_, 1);
-    Serial.println(F("C avg"));
+    Serial.println(F("C avg (heat PI only)"));
     return true;
   }
 
@@ -95,20 +96,18 @@ public:
 
   float resultKp() const { return resultKp_; }
   float resultKi() const { return resultKi_; }
-  float resultKd() const { return resultKd_; }
-  uint8_t resultFanMixMax() const { return resultFanMixMax_; }
 
   Phase update(float avgTempC, float maxTempC, float spreadC, uint32_t nowMs, float &heaterDutyOut,
                uint8_t &fanPwmOut) {
     heaterDutyOut = 0.0f;
-    fanPwmOut = FAN_HEAT_MIN_PWM;
+    fanPwmOut = AUTOTUNE_PREHEAT_FAN_PWM;
 
     if (phase_ == Phase::Idle || phase_ == Phase::Done || phase_ == Phase::Failed) {
       return phase_;
     }
 
-    if (maxTempC >= TARGET_MAX_C - 1.0f) {
-      fail(F("autotune: abort — max sensor at safety limit"));
+    if (maxTempC >= emergencyCutoffForTarget(setpointC_)) {
+      fail(F("autotune: abort — max sensor at emergency limit"));
       return phase_;
     }
 
@@ -124,8 +123,8 @@ public:
         fail(F("autotune: abort — preheat timeout"));
         return phase_;
       }
-      if (avgTempC >= preheatTargetC()) {
-        enterRelay(avgTempC, nowMs);
+      if (avgTempC >= preheatTargetC() || maxTempC >= setpointC_ - 2.0f) {
+        enterRelay(avgTempC, maxTempC, spreadC, nowMs);
       } else {
         heaterDutyOut = AUTOTUNE_PREHEAT_DUTY;
       }
@@ -137,27 +136,39 @@ public:
       return phase_;
     }
 
+    if (cycleCount_ == 0 && nowMs - phaseStartMs_ > AUTOTUNE_RELAY_STALL_MS) {
+      Serial.print(F("autotune: relay stalled — avg "));
+      Serial.print(avgTempC, 1);
+      Serial.print(F("C max "));
+      Serial.print(maxTempC, 1);
+      Serial.println(F("C (spread too large for avg to cross setpoint?)"));
+      fail(F("autotune: abort — no oscillation"));
+      return phase_;
+    }
+
+    const float pv = useMaxSensorPv_ ? maxTempC : avgTempC;
+
     spreadSum_ += spreadC;
     ++spreadSamples_;
 
-    if (avgTempC > peakSinceCross_) {
-      peakSinceCross_ = avgTempC;
+    if (pv > peakSinceCross_) {
+      peakSinceCross_ = pv;
     }
-    if (avgTempC < valleySinceCross_) {
-      valleySinceCross_ = avgTempC;
+    if (pv < valleySinceCross_) {
+      valleySinceCross_ = pv;
     }
 
     bool heatOn = false;
-    if (avgTempC <= relayLow_) {
+    if (pv <= relayLow_) {
       heatOn = true;
-    } else if (avgTempC >= relayHigh_) {
+    } else if (pv >= relayHigh_) {
       heatOn = false;
     } else {
       heatOn = !aboveSetpoint_;
     }
     heaterDutyOut = heatOn ? 100.0f : 0.0f;
 
-    const bool nowAbove = avgTempC >= setpointC_;
+    const bool nowAbove = pv >= setpointC_;
     if (nowAbove != aboveSetpoint_) {
       onSetpointCrossing(nowMs);
       aboveSetpoint_ = nowAbove;
@@ -167,14 +178,18 @@ public:
   }
 
 private:
-  void enterRelay(float avgTempC, uint32_t nowMs) {
+  void enterRelay(float avgTempC, float maxTempC, float spreadC, uint32_t nowMs) {
     phase_ = Phase::Relay;
     phaseStartMs_ = nowMs;
-    aboveSetpoint_ = avgTempC >= setpointC_;
-    peakSinceCross_ = avgTempC;
-    valleySinceCross_ = avgTempC;
+    useMaxSensorPv_ = spreadC > GOOD_SPREAD_C;
+    const float pv = useMaxSensorPv_ ? maxTempC : avgTempC;
+    aboveSetpoint_ = pv >= setpointC_;
+    peakSinceCross_ = pv;
+    valleySinceCross_ = pv;
     lastCrossMs_ = 0;
-    Serial.print(F("autotune: relay test started ("));
+    Serial.print(F("autotune: relay "));
+    Serial.print(useMaxSensorPv_ ? F("max-sensor") : F("avg"));
+    Serial.print(F(" ("));
     Serial.print((nowMs - sessionStartMs_) / 1000UL);
     Serial.println(F("s preheat)"));
   }
@@ -191,6 +206,7 @@ private:
     spreadSamples_ = 0;
     cycleCount_ = 0;
     aboveSetpoint_ = false;
+    useMaxSensorPv_ = false;
   }
 
   void onSetpointCrossing(uint32_t nowMs) {
@@ -239,7 +255,6 @@ private:
     const float ku = (4.0f * 100.0f) / (PI * avgAmplitude);
     resultKp_ = 0.45f * ku;
     resultKi_ = resultKp_ / (2.2f * avgPeriodSec);
-    resultKd_ = resultKp_ * avgPeriodSec / 6.3f;
 
     if (resultKp_ < 0.5f) {
       resultKp_ = 0.5f;
@@ -248,30 +263,15 @@ private:
       resultKi_ = resultKp_ / 3.0f;
     }
 
-    resultFanMixMax_ = FAN_MIX_MAX_PWM;
-    const float spreadAvg =
-        spreadSamples_ > 0 ? spreadSum_ / static_cast<float>(spreadSamples_) : GOOD_SPREAD_C;
-    if (spreadAvg > GOOD_SPREAD_C) {
-      const float boost = 1.0f + ((spreadAvg - GOOD_SPREAD_C) / 10.0f);
-      int boosted = static_cast<int>(static_cast<float>(FAN_MIX_MAX_PWM) * boost);
-      if (boosted > static_cast<int>(FAN_MAX_PWM) - 20) {
-        boosted = FAN_MAX_PWM - 20;
-      }
-      resultFanMixMax_ = static_cast<uint8_t>(boosted);
-    }
-
     phase_ = Phase::Done;
     Serial.print(F("autotune: done in "));
     Serial.print((nowMs - sessionStartMs_) / 1000UL);
     Serial.println(F("s"));
-    Serial.print(F("  Kp="));
+    Serial.print(F("  heat Kp="));
     Serial.print(resultKp_, 3);
     Serial.print(F(" Ki="));
-    Serial.print(resultKi_, 4);
-    Serial.print(F(" Kd="));
-    Serial.print(resultKd_, 3);
-    Serial.print(F(" fanMixMax="));
-    Serial.println(resultFanMixMax_);
+    Serial.println(resultKi_, 4);
+    Serial.println(F("  tune heat PI: pid save after autotune"));
   }
 
   void fail(const __FlashStringHelper *reason) {
@@ -295,10 +295,9 @@ private:
   uint16_t spreadSamples_;
   uint8_t cycleCount_;
   bool aboveSetpoint_;
+  bool useMaxSensorPv_;
   uint32_t sessionStartMs_;
   uint32_t phaseStartMs_;
   float resultKp_;
   float resultKi_;
-  float resultKd_;
-  uint8_t resultFanMixMax_;
 };

include/settings_store.h

@@ -6,12 +6,13 @@
 #include "config.h"
 
 // After TuningData (15 bytes) + checksum (1 byte) at address 0
-static const uint16_t SETTINGS_MAGIC = 0xDA7E;
+static const uint16_t SETTINGS_MAGIC = 0xDA7F;
 static const int SETTINGS_EEPROM_ADDR = 16;
 
 struct SettingsData {
   uint16_t magic = 0;
   float targetC = TARGET_TEMP_C;
+  uint8_t stirFanPwm = 0; // 0 = use FAN_STIR_PWM from config
 };
 
 inline uint8_t settingsChecksum(const SettingsData &data) {
@@ -39,8 +40,24 @@ inline void settingsSave(const SettingsData &data) {
 
 inline void settingsSaveTarget(float targetC) {
   SettingsData data;
+  if (settingsLoad(data)) {
+    data.targetC = targetC;
+  } else {
     data.magic = SETTINGS_MAGIC;
     data.targetC = targetC;
+    data.stirFanPwm = 0;
+  }
+  settingsSave(data);
+}
+
+inline void settingsSaveStirFan(uint8_t stirFanPwm) {
+  SettingsData data;
+  if (settingsLoad(data)) {
+    data.stirFanPwm = stirFanPwm;
+  } else {
+    data.magic = SETTINGS_MAGIC;
+    data.stirFanPwm = stirFanPwm;
+  }
   settingsSave(data);
 }
 

include/thermal_controller.h

@@ -3,6 +3,7 @@
 #include <Arduino.h>
 
 #include "config.h"
+#include "fan_characterize.h"
 #include "pid_autotuner.h"
 #include "pid_controller.h"
 #include "settings_store.h"
@@ -10,20 +11,24 @@
 
 class ThermalController {
 public:
-  enum class HeaterBlock : uint8_t { None, Cutoff, Corner, Allow, Autotune };
+  enum class HeaterBlock : uint8_t { None, Cutoff, Corner, Autotune, FanChars };
 
   ThermalController()
-      : pid_(PID_KP, PID_KI, PID_KD, 0.0f, 100.0f),
+      : heatPi_(HEAT_PI_KP, HEAT_PI_KI, 0.0f, 0.0f, 100.0f),
         autotuner_(),
+        fanchars_(),
         targetTempC_(TARGET_TEMP_C),
         heaterDutyPercent_(0.0f),
         heaterAllowancePercent_(100.0f),
         cornerSpreadC_(0.0f),
         lastMaxTempC_(0.0f),
-        fanPwm_(FAN_MAX_PWM),
-        fanMixMax_(FAN_MIX_MAX_PWM),
-        adaptiveEnabled_(false),
+        regulatingFanPwm_(0),
+        stirFanPwm_(FAN_STIR_PWM),
+        fanManualPwm_(0),
+        fanPwm_(0),
+        tuningLoaded_(false),
         fanIdleOverride_(false),
+        fanManualActive_(false),
         sensorWarmValid_(false),
         cutoffActive_(false),
         failSafeActive_(true),
@@ -40,13 +45,13 @@ public:
     pinMode(FAN_PIN, OUTPUT);
     pinMode(HEATER_PIN, OUTPUT);
     digitalWrite(HEATER_PIN, LOW);
+    writeFan(0);
 
-    pid_.setSetpoint(targetTempC_);
-    pid_.reset();
+    heatPi_.setSetpoint(targetTempC_);
+    heatPi_.reset();
     heaterCycleStartMs_ = millis();
     lastHeaterUpdateMs_ = 0;
     failSafeActive_ = true;
-    fanPwm_ = FAN_MAX_PWM;
     cornerSpreadC_ = 0.0f;
     lastMaxTempC_ = 0.0f;
     sensorWarmValid_ = false;
@@ -59,58 +64,64 @@ public:
     TuningData stored;
     if (tuningLoad(stored)) {
       applyTuning(stored);
-      Serial.println(F("Loaded learned PID from EEPROM"));
+      Serial.println(F("Loaded learned PI from EEPROM"));
       printTuning();
     }
 
     SettingsData settings;
-    if (settingsLoad(settings) && settings.targetC >= TARGET_MIN_C &&
-        settings.targetC <= TARGET_MAX_C) {
+    if (settingsLoad(settings)) {
+      if (settings.stirFanPwm > 0) {
+        stirFanPwm_ = settings.stirFanPwm;
+      }
+      if (settings.targetC >= TARGET_MIN_C && settings.targetC <= TARGET_MAX_C) {
         setTarget(settings.targetC, false);
       }
     }
+  }
 
   void applyTuning(const TuningData &data) {
-    pid_.setTunings(data.kp, data.ki, data.kd);
-    fanMixMax_ = data.fanMixMax;
-    adaptiveEnabled_ = true;
+    heatPi_.setTunings(data.heatKp, data.heatKi, 0.0f);
+    tuningLoaded_ = true;
   }
 
   void clearTuning() {
-    adaptiveEnabled_ = false;
-    fanMixMax_ = FAN_MIX_MAX_PWM;
-    pid_.setTunings(PID_KP, PID_KI, PID_KD);
+    tuningLoaded_ = false;
+    heatPi_.setTunings(HEAT_PI_KP, HEAT_PI_KI, 0.0f);
     tuningClear();
-    pid_.reset();
-    Serial.println(F("PID reset to defaults"));
+    heatPi_.reset();
+    Serial.println(F("PI reset to defaults"));
   }
 
   void printTuning() const {
-    Serial.print(F("PID Kp="));
-    Serial.print(pidKp(), 3);
+    Serial.print(F("Heat PI Kp="));
+    Serial.print(heatPi_.kp(), 3);
     Serial.print(F(" Ki="));
-    Serial.print(pidKi(), 4);
-    Serial.print(F(" Kd="));
-    Serial.print(pidKd(), 3);
-    Serial.print(F(" fanMixMax="));
-    Serial.print(fanMixMax_);
-    Serial.print(F(" adaptive="));
-    Serial.println(adaptiveEnabled_ ? F("yes") : F("no"));
+    Serial.print(heatPi_.ki(), 4);
+    Serial.print(F("  tuned="));
+    Serial.println(tuningLoaded_ ? F("yes") : F("no"));
   }
 
-  float pidKp() const { return pid_.kp(); }
-  float pidKi() const { return pid_.ki(); }
-  float pidKd() const { return pid_.kd(); }
+  void saveTuningToEeprom() {
+    TuningData data;
+    data.magic = TUNING_MAGIC;
+    data.heatKp = heatPi_.kp();
+    data.heatKi = heatPi_.ki();
+    tuningSave(data);
+    tuningLoaded_ = true;
+    Serial.println(F("Saved PI to EEPROM"));
+  }
 
-  bool isAdaptive() const { return adaptiveEnabled_; }
+  float heatKp() const { return heatPi_.kp(); }
+  float heatKi() const { return heatPi_.ki(); }
+
+  bool isTuningLoaded() const { return tuningLoaded_; }
 
   bool startAutotune(float setpointC) {
-    if (autotuner_.isActive()) {
+    if (autotuner_.isActive() || fanchars_.isActive()) {
       return false;
     }
-    adaptiveEnabled_ = false;
     cutoffActive_ = false;
-    pid_.reset();
+    heatPi_.reset();
     return autotuner_.start(setpointC);
   }
 
@@ -128,28 +139,114 @@ public:
 
   float autotunePreheatTargetC() const { return autotuner_.preheatTargetC(); }
 
+  bool startFanCharacterize(float maxCornerC, float avgTempC) {
+    if (autotuner_.isActive() || fanchars_.isActive()) {
+      return false;
+    }
+    stopFanTest();
+    cutoffActive_ = false;
+    heatPi_.reset();
+    setTarget(0.0f, false);
+    return fanchars_.start(maxCornerC, avgTempC);
+  }
+
+  void stopFanCharacterize() {
+    fanchars_.abort();
+    forceHeaterOff();
+    writeFan(0);
+  }
+
+  bool isFanCharacterizeActive() const { return fanchars_.isActive(); }
+
+  uint32_t fanCharacterizeElapsedMs(uint32_t nowMs) const { return fanchars_.elapsedMs(nowMs); }
+
+  const char *fanCharacterizePhaseName() const { return fanchars_.phaseName(); }
+
+  uint8_t fanCharacterizeProfileIndex() const { return fanchars_.profileIndex(); }
+
+  uint8_t fanCharacterizeProfileCount() const { return fanchars_.profileCount(); }
+
+  uint8_t fanCharacterizeFanPwm() const { return fanchars_.currentFanPwm(); }
+
+  bool isFanCharacterizeRefineRun() const { return fanchars_.isRefineRun(); }
+
+  float fanCharacterizeHeaterPct() const { return fanchars_.heaterPct(); }
+
+  uint8_t stirFanPwm() const { return stirFanPwm_; }
+
+  bool isFanManualOverride() const { return fanManualActive_ && !isIdle(); }
+
+  bool setRegulatingFanManual(uint8_t pwm) {
+    if (isIdle()) {
+      return false;
+    }
+    fanManualPwm_ = pwm;
+    fanManualActive_ = true;
+    return true;
+  }
+
+  void clearRegulatingFanManual() {
+    fanManualActive_ = false;
+  }
+
+  bool setStirFanPwm(uint8_t pwm, bool persist = true) {
+    if (pwm == 0) {
+      return false;
+    }
+    stirFanPwm_ = pwm;
+    if (persist) {
+      settingsSaveStirFan(pwm);
+    }
+    return true;
+  }
+
+  void logFanCharacterizeIfDue(const float *sensorTemps, const bool *sensorValid, uint8_t sensorCount,
+                               float avgTempC, float minTempC, float maxTempC, float spreadC,
+                               uint32_t nowMs) {
+    fanchars_.logIfDue(sensorTemps, sensorValid, sensorCount, avgTempC, minTempC, maxTempC,
+                       spreadC, nowMs);
+  }
+
+  bool saveStirFanFromCharacterize() {
+    if (fanchars_.phase() != FanCharacterize::Phase::Done) {
+      return false;
+    }
+    const uint8_t winner = fanchars_.winnerFanPwm();
+    if (winner == 0) {
+      return false;
+    }
+    stirFanPwm_ = winner;
+    settingsSaveStirFan(winner);
+    Serial.print(F("stir fan "));
+    Serial.println(winner);
+    fanchars_.reset();
+    return true;
+  }
+
   bool commitAutotuneIfDone() {
     if (autotuner_.phase() != PidAutotuner::Phase::Done) {
       return false;
     }
 
+    heatPi_.setTunings(autotuner_.resultKp(), autotuner_.resultKi(), 0.0f);
+    heatPi_.reset();
+
     TuningData data;
     data.magic = TUNING_MAGIC;
-    data.kp = autotuner_.resultKp();
-    data.ki = autotuner_.resultKi();
-    data.kd = autotuner_.resultKd();
-    data.fanMixMax = autotuner_.resultFanMixMax();
+    data.heatKp = autotuner_.resultKp();
+    data.heatKi = autotuner_.resultKi();
     tuningSave(data);
-    applyTuning(data);
+    tuningLoaded_ = true;
     autotuner_.reset();
-    Serial.println(F("Saved learned PID to EEPROM"));
+    Serial.println(F("Saved heat PI to EEPROM"));
     return true;
   }
 
   void setTarget(float targetC, bool persist = true) {
     targetTempC_ = targetC;
-    pid_.setSetpoint(targetC);
-    pid_.reset();
+    heatPi_.setSetpoint(targetC);
+    heatPi_.reset();
+    fanManualActive_ = false;
     cutoffActive_ = false;
     if (targetC > 0.0f) {
       fanIdleOverride_ = false;
@@ -202,11 +299,13 @@ public:
 
   bool isIdle() const { return targetTempC_ <= 0.0f; }
 
+  float emergencyCutoffC() const { return emergencyCutoffForTarget(targetTempC_); }
+
   float cutoffThreshold() const {
     if (isIdle()) {
       return INFINITY;
     }
-    return targetTempC_ * (1.0f + OVERTEMP_FRACTION);
+    return emergencyCutoffC();
   }
 
   bool isCutoffActive() const { return cutoffActive_; }
@@ -237,7 +336,12 @@ public:
 
   void stopFanTest() { fanTestActive_ = false; }
 
-  float maxHeatStopAt(float avgTempC) const { return maxHeatStopTemp(avgTempC); }
+  float maxHeatStopAt(float avgTempC) const {
+    if (isIdle()) {
+      return INFINITY;
+    }
+    return maxHeatStopTemp(avgTempC);
+  }
 
   const char *heaterBlockReason() const {
     switch (heaterBlock_) {
@@ -245,15 +349,19 @@ public:
       return "cutoff";
     case HeaterBlock::Corner:
       return "corner";
-    case HeaterBlock::Allow:
-      return "allow";
     case HeaterBlock::Autotune:
       return "autotune";
+    case HeaterBlock::FanChars:
+      return "fanchars";
     default:
       return "none";
     }
   }
 
+  const char *regulatingModeName() const {
+    return tuningLoaded_ ? "regulating" : "manual";
+  }
+
   void update(float avgTempC, float maxTempC, float cornerSpreadC, uint32_t nowMs) {
     failSafeActive_ = false;
     noteSensorMax(maxTempC);
@@ -261,8 +369,13 @@ public:
     heaterBlock_ = HeaterBlock::None;
 
     cornerSpreadC_ =
-        SPREAD_EMA_ALPHA * cornerSpreadC +
-        (1.0f - SPREAD_EMA_ALPHA) * cornerSpreadC_;
+        SPREAD_EMA_ALPHA * cornerSpreadC_ +
+        (1.0f - SPREAD_EMA_ALPHA) * cornerSpreadC;
+
+    if (fanchars_.isActive()) {
+      updateFanCharacterize(avgTempC, maxTempC, nowMs);
+      return;
+    }
 
     if (autotuner_.isActive()) {
       updateAutotune(avgTempC, maxTempC, nowMs);
@@ -272,21 +385,16 @@ public:
     if (isIdle()) {
       forceHeaterOff();
       cutoffActive_ = false;
-      pid_.reset();
+      heatPi_.reset();
       lastHeaterUpdateMs_ = nowMs;
       applyFan(nowMs);
       return;
     }
 
-    if (adaptiveEnabled_) {
-      updateAdaptive(avgTempC, maxTempC, nowMs);
-    } else {
-      updateLegacy(avgTempC, maxTempC, nowMs);
-    }
-
+    updateRegulating(avgTempC, maxTempC, nowMs);
     lastHeaterUpdateMs_ = nowMs;
     applyHeaterBurst(nowMs);
-    applyFan(nowMs);
+    writeFan(regulatingFanPwm_);
   }
 
   void enterFailSafe() {
@@ -294,8 +402,9 @@ public:
     cutoffActive_ = false;
     forceHeaterOff();
     applyFan(millis());
-    pid_.reset();
+    heatPi_.reset();
     autotuner_.abort();
+    fanchars_.abort();
   }
 
   void forceHeaterOff() {
@@ -307,19 +416,49 @@ public:
 
   void writeFan(uint8_t pwm) {
     fanPwm_ = pwm;
-    if (pwm == 0) {
-      // Re-assert output and stop Timer0 PWM on D5 — analogWrite(0) can leave the pin driving
     pinMode(FAN_PIN, OUTPUT);
-      digitalWrite(FAN_PIN, LOW);
-    } else {
-      analogWrite(FAN_PIN, pwm);
+
+    if (FAN_PWM_INVERT) {
+      if (pwm == 0) {
+        digitalWrite(FAN_PIN, HIGH);
+        return;
       }
+      if (pwm >= 254) {
+        digitalWrite(FAN_PIN, LOW);
+        return;
+      }
+      analogWrite(FAN_PIN, static_cast<uint8_t>(255 - pwm));
+      return;
+    }
+
+    if (pwm == 0) {
+      digitalWrite(FAN_PIN, LOW);
+      return;
+    }
+    if (pwm >= 254) {
+      digitalWrite(FAN_PIN, HIGH);
+      return;
+    }
+    analogWrite(FAN_PIN, pwm);
   }
 
 private:
+  void updateFanCharacterize(float avgTempC, float maxTempC, uint32_t nowMs) {
+    float duty = 0.0f;
+    uint8_t fan = 0;
+    fanchars_.update(avgTempC, maxTempC, cornerSpreadC_, nowMs, duty, fan);
+
+    heaterDutyPercent_ = duty;
+    heaterAllowancePercent_ = duty;
+    heaterBlock_ = duty > 0.0f ? HeaterBlock::FanChars : HeaterBlock::None;
+    applyHeaterBurst(nowMs);
+    writeFan(fan);
+    lastHeaterUpdateMs_ = nowMs;
+  }
+
   void updateAutotune(float avgTempC, float maxTempC, uint32_t nowMs) {
     float duty = 0.0f;
-    uint8_t fan = FAN_HEAT_MIN_PWM;
+    uint8_t fan = stirFanPwm_;
     autotuner_.update(avgTempC, maxTempC, cornerSpreadC_, nowMs, duty, fan);
 
     heaterDutyPercent_ = duty;
@@ -327,99 +466,47 @@ private:
     heaterOn_ = duty >= 50.0f;
     digitalWrite(HEATER_PIN, heaterOn_ ? HIGH : LOW);
     heaterBlock_ = duty > 0.0f ? HeaterBlock::None : HeaterBlock::Autotune;
-    writeFan(fan);
+    writeFan(fanManualActive_ ? fanManualPwm_ : stirFanPwm_);
     lastHeaterUpdateMs_ = nowMs;
     commitAutotuneIfDone();
   }
 
-  void updateAdaptive(float avgTempC, float maxTempC, uint32_t nowMs) {
-    const float cutoff = cutoffThreshold();
-
-    if (maxTempC >= cutoff) {
+  void updateRegulating(float avgTempC, float maxTempC, uint32_t nowMs) {
+    const float cutoffC = emergencyCutoffC();
+    if (maxTempC >= cutoffC) {
       cutoffActive_ = true;
       heaterDutyPercent_ = 0.0f;
       heaterAllowancePercent_ = 0.0f;
-      heaterOn_ = false;
+      regulatingFanPwm_ = FAN_MAX_PWM;
       heaterBlock_ = HeaterBlock::Cutoff;
-      pid_.reset();
+      heatPi_.reset();
       return;
     }
 
-    if (cutoffActive_ && maxTempC <= targetTempC_) {
+    if (cutoffActive_ && maxTempC < cutoffC - CUTOFF_RECOVERY_BAND_C) {
       cutoffActive_ = false;
-      pid_.reset();
+      heatPi_.reset();
     }
 
     if (cutoffActive_) {
       heaterBlock_ = HeaterBlock::Cutoff;
+      regulatingFanPwm_ = FAN_MAX_PWM;
       return;
     }
 
-    if (shouldLimitMaxCorner(avgTempC) && maxTempC >= maxHeatStopTemp(avgTempC)) {
-      heaterDutyPercent_ = 0.0f;
-      heaterAllowancePercent_ = 0.0f;
-      heaterBlock_ = HeaterBlock::Corner;
-      pid_.reset();
-      return;
-    }
+    heaterAllowancePercent_ = allowanceFromMaxCorner(maxTempC, avgTempC);
 
-    float duty = pid_.compute(avgTempC, nowMs);
-    const float below = targetTempC_ - avgTempC;
-    if (below > 8.0f) {
-      const float floor = below > 15.0f ? 75.0f : 60.0f;
-      if (duty < floor) {
-        duty = floor;
-      }
-    }
-    const float maxDuty = heaterMaxDuty(avgTempC);
-    if (duty > maxDuty) {
-      duty = maxDuty;
-    }
-    heaterAllowancePercent_ = maxDuty;
-    heaterDutyPercent_ = duty;
-  }
-
-  void updateLegacy(float avgTempC, float maxTempC, uint32_t nowMs) {
-    const float cutoff = cutoffThreshold();
-
-    if (maxTempC >= cutoff) {
-      cutoffActive_ = true;
-      heaterDutyPercent_ = 0.0f;
-      heaterAllowancePercent_ = 0.0f;
-      heaterOn_ = false;
-      heaterBlock_ = HeaterBlock::Cutoff;
-      pid_.reset();
-      return;
-    }
-
-    if (cutoffActive_ && maxTempC <= targetTempC_) {
-      cutoffActive_ = false;
-      pid_.reset();
-    }
-
-    if (cutoffActive_) {
-      heaterBlock_ = HeaterBlock::Cutoff;
-      return;
-    }
-
-    if (shouldLimitMaxCorner(avgTempC) && maxTempC >= maxHeatStopTemp(avgTempC)) {
-      heaterDutyPercent_ = 0.0f;
-      heaterAllowancePercent_ = 0.0f;
-      heaterBlock_ = HeaterBlock::Corner;
-      pid_.reset();
-      return;
-    }
-
-    const float pidOut = pid_.compute(avgTempC, nowMs);
-    heaterAllowancePercent_ = heaterAllowancePercent(avgTempC, maxTempC);
-    float duty = pidOut;
+    float duty = heatPi_.compute(avgTempC, nowMs);
+    duty = clampPercent(duty);
     if (duty > heaterAllowancePercent_) {
       duty = heaterAllowancePercent_;
+      if (heaterAllowancePercent_ < 100.0f) {
+        heaterBlock_ = HeaterBlock::Corner;
       }
-    if (duty <= 0.0f && heaterAllowancePercent_ <= 0.0f) {
-      heaterBlock_ = HeaterBlock::Allow;
     }
-    heaterDutyPercent_ = applyHeaterRamp(duty, avgTempC, nowMs);
+    heaterDutyPercent_ = duty;
+
+    regulatingFanPwm_ = fanManualActive_ ? fanManualPwm_ : stirFanPwm_;
   }
 
   static float clampPercent(float value) {
@@ -432,37 +519,25 @@ private:
     return value;
   }
 
-  bool isBalancedChamber() const { return cornerSpreadC_ <= GOOD_SPREAD_C; }
-
   bool shouldLimitMaxCorner(float avgTempC) const {
     return avgTempC >= targetTempC_ - CORNER_LIMIT_BAND_C;
   }
 
   float maxHeatStopTemp(float avgTempC) const {
-    if (avgTempC >= targetTempC_) {
-      return targetTempC_;
+    if (!shouldLimitMaxCorner(avgTempC)) {
+      return emergencyCutoffC();
     }
-
-    float stopAt = targetTempC_;
-    if (isBalancedChamber()) {
-      stopAt = targetTempC_ + BALANCED_MAX_ABOVE_TARGET_C;
-    } else {
-      stopAt = targetTempC_ + cornerSpreadC_ * SPREAD_HEADROOM_FACTOR + 1.0f;
-    }
-
-    const float cutoff = cutoffThreshold();
-    if (stopAt > cutoff) {
-      stopAt = cutoff;
-    }
-    return stopAt;
+    return emergencyCutoffC() - CORNER_STOP_MARGIN_C;
   }
 
   float allowanceFromMaxCorner(float maxTempC, float avgTempC) const {
+    const float cutoffC = emergencyCutoffC();
     if (!shouldLimitMaxCorner(avgTempC)) {
-      return 100.0f;
+      // Heat-up: only taper when a hot corner nears the dynamic cutoff
+      if (maxTempC >= cutoffC - 3.0f) {
+        const float headroom = cutoffC - maxTempC;
+        return clampPercent((headroom / 3.0f) * 100.0f);
       }
-
-    if (isBalancedChamber() && avgTempC < targetTempC_) {
       return 100.0f;
     }
 
@@ -479,111 +554,6 @@ private:
     return clampPercent((headroom / MAX_TEMP_HEADROOM_C) * 100.0f);
   }
 
-  float allowanceFromAverage(float avgTempC) const {
-    if (avgTempC >= targetTempC_) {
-      return 0.0f;
-    }
-
-    const float below = targetTempC_ - avgTempC;
-    if (below >= APPROACH_BAND_C) {
-      return 100.0f;
-    }
-
-    return clampPercent((below / APPROACH_BAND_C) * 100.0f);
-  }
-
-  float heaterMaxDuty(float avgTempC) const {
-    if (avgTempC >= targetTempC_) {
-      return HEATER_MAX_DUTY_NEAR;
-    }
-
-    const float below = targetTempC_ - avgTempC;
-    if (below >= HEATER_COLD_BELOW_C) {
-      return HEATER_MAX_DUTY_COLD;
-    }
-    if (below >= HEATER_WARM_BELOW_C) {
-      return HEATER_MAX_DUTY_MID;
-    }
-    return HEATER_MAX_DUTY_NEAR;
-  }
-
-  float heaterAllowancePercent(float avgTempC, float maxTempC) const {
-    const float fromMax = allowanceFromMaxCorner(maxTempC, avgTempC);
-    const float fromAvg = allowanceFromAverage(avgTempC);
-    float allowance = fromMax < fromAvg ? fromMax : fromAvg;
-    const float maxDuty = heaterMaxDuty(avgTempC);
-    if (allowance > maxDuty) {
-      allowance = maxDuty;
-    }
-    return allowance;
-  }
-
-  float applyHeaterRamp(float requestedDuty, float avgTempC, uint32_t nowMs) {
-    const float maxDuty = heaterMaxDuty(avgTempC);
-    if (requestedDuty > maxDuty) {
-      requestedDuty = maxDuty;
-    }
-
-    if (lastHeaterUpdateMs_ > 0 && requestedDuty > heaterDutyPercent_) {
-      const float dt = static_cast<float>(nowMs - lastHeaterUpdateMs_) / 1000.0f;
-      const float maxUp = heaterDutyPercent_ + HEATER_SLEW_UP_PER_S * dt;
-      if (requestedDuty > maxUp) {
-        requestedDuty = maxUp;
-      }
-    }
-
-    return requestedDuty;
-  }
-
-  uint8_t fanPwmForHeatUp() const {
-    if (heaterDutyPercent_ <= 0.0f) {
-      return 0;
-    }
-
-    const float below = targetTempC_ - lastAvgTempC_;
-    uint8_t heatFan = 0;
-    if (below <= FAN_OFF_BELOW_TARGET_C) {
-      const uint8_t span = FAN_HEAT_MAX_PWM - FAN_HEAT_MIN_PWM;
-      heatFan = FAN_HEAT_MIN_PWM +
-                static_cast<uint8_t>((heaterDutyPercent_ / 100.0f) * static_cast<float>(span));
-    } else if (below < FAN_RAMP_BELOW_TARGET_C) {
-      const float spanC = FAN_RAMP_BELOW_TARGET_C - FAN_OFF_BELOW_TARGET_C;
-      const float t = (FAN_RAMP_BELOW_TARGET_C - below) / spanC;
-      heatFan = static_cast<uint8_t>(t * static_cast<float>(FAN_HEAT_MIN_PWM));
-    }
-
-    uint8_t mixFan = 0;
-    if (below <= FAN_OFF_BELOW_TARGET_C || cornerSpreadC_ > GOOD_SPREAD_C) {
-      mixFan = fanPwmForCornerSpread();
-    }
-
-    uint8_t duty = heatFan > mixFan ? heatFan : mixFan;
-
-    if (lastAvgTempC_ >= targetTempC_ - 2.0f && lastMaxTempC_ > targetTempC_ &&
-        duty < FAN_MAX_PWM) {
-      duty = FAN_MAX_PWM;
-    }
-    return duty;
-  }
-
-  uint8_t fanPwmForCornerSpread() const {
-    if (cornerSpreadC_ <= SPREAD_DEADBAND_C) {
-      return 0;
-    }
-
-    float spread = cornerSpreadC_;
-    if (spread > SPREAD_FULL_MIX_C) {
-      spread = SPREAD_FULL_MIX_C;
-    }
-
-    const float t =
-        (spread - SPREAD_DEADBAND_C) / (SPREAD_FULL_MIX_C - SPREAD_DEADBAND_C);
-    const uint8_t mixMax = fanMixMax_;
-    const uint8_t mixMin = FAN_MIX_MIN_PWM;
-    const uint8_t span = mixMax > mixMin ? mixMax - mixMin : 0;
-    return mixMin + static_cast<uint8_t>(t * static_cast<float>(span));
-  }
-
   void applyHeaterBurst(uint32_t nowMs) {
     if (heaterDutyPercent_ <= 0.0f) {
       forceHeaterOff();
@@ -614,7 +584,7 @@ private:
     }
 
     if (isIdle()) {
-      if (!sensorWarmValid_ || lastMaxTempC_ >= IDLE_AUTO_FAN_OFF_TEMP_C) {
+      if (sensorWarmValid_ && lastMaxTempC_ >= IDLE_AUTO_FAN_OFF_TEMP_C) {
         writeFan(FAN_MAX_PWM);
       } else if (fanIdleOverride_) {
         writeFan(FAN_IDLE_PWM);
@@ -628,22 +598,23 @@ private:
       writeFan(FAN_MAX_PWM);
       return;
     }
-
-    uint8_t duty = fanPwmForHeatUp();
-    writeFan(duty);
   }
 
-  PidController pid_;
+  PidController heatPi_;
   PidAutotuner autotuner_;
+  FanCharacterize fanchars_;
   float targetTempC_;
   float heaterDutyPercent_;
   float heaterAllowancePercent_;
   float cornerSpreadC_;
   float lastMaxTempC_;
+  uint8_t regulatingFanPwm_;
+  uint8_t stirFanPwm_;
+  uint8_t fanManualPwm_;
   uint8_t fanPwm_;
-  uint8_t fanMixMax_;
-  bool adaptiveEnabled_;
+  bool tuningLoaded_;
   bool fanIdleOverride_;
+  bool fanManualActive_;
   bool sensorWarmValid_;
   bool cutoffActive_;
   bool failSafeActive_;

include/tuning_store.h

@@ -5,15 +5,13 @@
 
 #include "config.h"
 
-static const uint16_t TUNING_MAGIC = 0xDA7A;
+static const uint16_t TUNING_MAGIC = 0xDA7C;
 static const int TUNING_EEPROM_ADDR = 0;
 
 struct TuningData {
   uint16_t magic = 0;
-  float kp = PID_KP;
-  float ki = PID_KI;
-  float kd = PID_KD;
-  uint8_t fanMixMax = FAN_MIX_MAX_PWM;
+  float heatKp = HEAT_PI_KP;
+  float heatKi = HEAT_PI_KI;
 };
 
 inline uint8_t tuningChecksum(const TuningData &data) {

pi-instructions.md

@@ -26,7 +26,7 @@ python3 scripts/capture_csv.py log
 # logs/dryer_YYYYMMDD_HHMMSS.csv
 ```
 
-**TUI keys:** `0` idle · `t` target · `p` presets · `f` fan on · `F` fan off · `l` toggle CSV log · `a` autotune · `:` raw command · `q` quit
+**TUI keys:** `0` idle · `t` target · `p` presets · `f` fan on · `F` fan off · `l` CSV log · `a` autotune · `c` fanchars · `:` command · `q` quit
 
 **Always-on logging**
 

platformio.ini

@@ -4,6 +4,7 @@ platform = atmelavr
 board = nanoatmega328
 framework = arduino
 monitor_speed = 115200
+build_flags = -flto
 lib_deps =
     adafruit/Adafruit SHT31 Library@^2.2.2
     adafruit/Adafruit BusIO@^1.16.1

scripts/capture_csv.py

@@ -9,6 +9,7 @@
 from __future__ import annotations
 
 import argparse
+import re
 import sys
 import time
 from datetime import datetime, timezone
@@ -19,6 +20,122 @@ FALLBACK_HEADER = (
     "fan_pct,cutoff,failsafe,ch2_t,ch2_h,ch3_t,ch3_h,ch4_t,ch4_h,ch5_t,ch5_h"
 )
 
+SENSOR_CHANNELS = [2, 3, 4, 5]
+
+# If no bytes at all arrive for this long, treat the device as hung (e.g. an
+# I2C bus lockup freezing the Arduino) rather than looping forever in silence.
+DEFAULT_STALL_TIMEOUT_S = 20.0
+
+_FAN_PCT_RE = re.compile(r"\((\d+)%\)")
+_FAN_PWM_RE = re.compile(r"^(\d+)/")
+
+
+def fan_pct_from_status(fan: str) -> int:
+    match = _FAN_PCT_RE.search(fan)
+    if match:
+        return int(match.group(1))
+    match = _FAN_PWM_RE.match(fan)
+    if match:
+        return (int(match.group(1)) * 100) // 255
+    return 0
+
+
+def target_c_from_status(target: str) -> str:
+    if target.startswith("idle"):
+        return "0.0"
+    if target.endswith("C"):
+        return target[:-1]
+    return target
+
+
+def build_csv_payload_from_status(data: dict, ms: int | None = None) -> str:
+    if ms is None:
+        ms = int(time.time() * 1000)
+
+    sensors = {ch: (temp, hum) for ch, temp, hum in data.get("sensor_list", [])}
+    parts = [
+        str(ms),
+        target_c_from_status(data["target"]),
+        data["avg"],
+        data["min"],
+        data["max"],
+        data["spread"],
+        data["heatlim"],
+        data["heater"],
+        str(fan_pct_from_status(data.get("fan", "0"))),
+        "1" if data.get("cutoff_active") == "YES" else "0",
+        "1" if data.get("failsafe") == "YES" else "0",
+    ]
+    for ch in SENSOR_CHANNELS:
+        if str(ch) in sensors:
+            temp, hum = sensors[str(ch)]
+            if temp == "ERR":
+                parts.extend(["", ""])
+            else:
+                parts.extend([temp, hum])
+        else:
+            parts.extend(["", ""])
+    return ",".join(parts)
+
+
+class CsvSession:
+    """Deferred CSV writer — no empty file until the first row lands."""
+
+    def __init__(self, path: Path):
+        self.path = path
+        self._fh = None
+        self._header_written = False
+        self.row_count = 0
+
+    def _ensure_open(self) -> None:
+        if self._fh is None:
+            self.path.parent.mkdir(parents=True, exist_ok=True)
+            self._fh = self.path.open("w", encoding="utf-8")
+
+    def _write_header(self) -> None:
+        if not self._header_written:
+            self._ensure_open()
+            assert self._fh is not None
+            self._fh.write(FALLBACK_HEADER + "\n")
+            self._header_written = True
+
+    def write_device_line(self, line: str) -> None:
+        if line.startswith("csv_hdr,"):
+            self._ensure_open()
+            assert self._fh is not None
+            device_header = line[len("csv_hdr,") :]
+            self._fh.write("wall_time," + device_header + "\n")
+            self._header_written = True
+            self._fh.flush()
+            return
+        if not line.startswith("csv,"):
+            return
+        self._write_header()
+        assert self._fh is not None
+        wall_time = datetime.now(timezone.utc).isoformat(timespec="seconds")
+        self._fh.write(wall_time + "," + line[len("csv,") :] + "\n")
+        self._fh.flush()
+        self.row_count += 1
+
+    def write_status(self, data: dict) -> None:
+        self._write_header()
+        assert self._fh is not None
+        wall_time = datetime.now(timezone.utc).isoformat(timespec="seconds")
+        payload = build_csv_payload_from_status(data)
+        self._fh.write(wall_time + "," + payload + "\n")
+        self._fh.flush()
+        self.row_count += 1
+
+    def close(self) -> None:
+        if self._fh is not None:
+            self._fh.close()
+            self._fh = None
+        if self.row_count == 0 and self.path.exists():
+            try:
+                self.path.unlink()
+            except OSError:
+                pass
+
 
 def detect_serial_port() -> str | None:
     by_id = Path("/dev/serial/by-id")
@@ -93,69 +210,71 @@ def enable_dryer_logging(ser, retries: int = 3) -> None:
     print("WARN: did not see 'OK csv logging on' — continuing anyway", file=sys.stderr)
 
 
-def write_csv_row(fh, line: str, header_written: list[bool]) -> None:
-    if line.startswith("csv_hdr,"):
-        device_header = line[len("csv_hdr,") :]
-        fh.write("wall_time," + device_header + "\n")
-        header_written[0] = True
-        fh.flush()
-        return
-    if not line.startswith("csv,"):
-        return
-    if not header_written[0]:
-        fh.write(FALLBACK_HEADER + "\n")
-        header_written[0] = True
-    wall_time = datetime.now(timezone.utc).isoformat(timespec="seconds")
-    fh.write(wall_time + "," + line[len("csv,") :] + "\n")
-    fh.flush()
+def log_notice(message: str) -> None:
+    stamp = datetime.now(timezone.utc).isoformat(timespec="seconds")
+    print(f"{stamp} {message}", file=sys.stderr)
 
 
 def cmd_log(args: argparse.Namespace) -> int:
+    from dryer_tui import parse_status
+
     port = resolve_port(args.port)
     out = args.output
     if out is None:
         out = args.log_dir / f"dryer_{datetime.now():%Y%m%d_%H%M%S}.csv"
-    out.parent.mkdir(parents=True, exist_ok=True)
 
+    stall_timeout = args.stall_timeout
     print(f"Logging {port} -> {out}", file=sys.stderr)
     if args.auto_log_on:
         print("Will send 'log on' after connect", file=sys.stderr)
 
-    header_written = False
-    with open_serial(port, args.baud) as ser, out.open("w", encoding="utf-8") as fh:
+    session = CsvSession(out)
+    with open_serial(port, args.baud) as ser:
         if args.auto_log_on:
             enable_dryer_logging(ser)
 
+        last_activity = time.monotonic()
         while True:
             try:
                 raw = ser.readline()
             except KeyboardInterrupt:
-                print("\nStopped.", file=sys.stderr)
+                print(f"\nStopped ({session.row_count} rows).", file=sys.stderr)
+                session.close()
                 return 0
+            except Exception as exc:
+                log_notice(
+                    f"ERROR: serial read failed ({exc}) — closing after "
+                    f"{session.row_count} rows"
+                )
+                session.close()
+                return 1
 
             if not raw:
+                if time.monotonic() - last_activity >= stall_timeout:
+                    log_notice(
+                        f"WARN: no data from {port} for {stall_timeout:.0f}s — "
+                        f"device likely hung (e.g. I2C bus lockup on the Arduino) "
+                        f"— closing after {session.row_count} rows"
+                    )
+                    session.close()
+                    return 1
                 continue
 
+            last_activity = time.monotonic()
             line = decode_line(raw)
-            if not line.startswith("csv_hdr,") and not line.startswith("csv,"):
-                if line:
+            parsed = parse_status(line)
+            if parsed:
+                session.write_status(parsed)
                 print(line)
                 continue
 
-            if line.startswith("csv_hdr,"):
-                device_header = line[len("csv_hdr,") :]
-                fh.write("wall_time," + device_header + "\n")
-                header_written = True
-                fh.flush()
+            if line.startswith("csv_hdr,") or line.startswith("csv,"):
+                session.write_device_line(line)
                 continue
 
-            if not header_written:
-                fh.write(FALLBACK_HEADER + "\n")
-                header_written = True
-
-            wall_time = datetime.now(timezone.utc).isoformat(timespec="seconds")
-            fh.write(wall_time + "," + line[len("csv,") :] + "\n")
-            fh.flush()
+            if line:
+                print(line)
+    return 0
 
 
 def cmd_tui(args: argparse.Namespace) -> int:
@@ -185,6 +304,15 @@ def build_parser() -> argparse.ArgumentParser:
         default=True,
         help="Send 'log on' after connect in log mode (default: on)",
     )
+    parser.add_argument(
+        "--stall-timeout",
+        type=float,
+        default=DEFAULT_STALL_TIMEOUT_S,
+        help=(
+            "log mode: seconds without any data before treating the device as "
+            f"hung and exiting (default: {DEFAULT_STALL_TIMEOUT_S:.0f})"
+        ),
+    )
 
     subparsers = parser.add_subparsers(dest="action")
     log_p = subparsers.add_parser("log", help="Headless CSV capture", add_help=False)
@@ -193,6 +321,7 @@ def build_parser() -> argparse.ArgumentParser:
     log_p.add_argument("-o", "--output", type=Path)
     log_p.add_argument("--log-dir", type=Path, default=Path("logs"))
     log_p.add_argument("--auto-log-on", action=argparse.BooleanOptionalAction, default=True)
+    log_p.add_argument("--stall-timeout", type=float, default=DEFAULT_STALL_TIMEOUT_S)
 
     tui_p = subparsers.add_parser("tui", help="Interactive curses dashboard")
     tui_p.add_argument("-p", "--port")

scripts/dryer_tui.py

@@ -7,14 +7,15 @@ import curses
 import re
 import sys
 import threading
+import time
 from collections import deque
 from dataclasses import dataclass, field
 from datetime import datetime
 from pathlib import Path
 
 from capture_csv import (
+    CsvSession,
     decode_line,
-    write_csv_row,
 )
 
 PRESETS: list[tuple[str, float]] = [
@@ -43,7 +44,7 @@ STATUS_RE = re.compile(
     r"htop=(?P<htop>\S+)\s+"
     r"hblk=(?P<hblk>\S+)\s+"
     r"ssr=(?P<ssr>on|off)\s+"
-    r"fan=(?P<fan>\S+)\s+"
+    r"fan=(?P<fan>\d+/255\([^)]+\)(?:\([^)]+\))?(?:\s+TEST)?)\s+"
     r"cutoff=(?P<cutoff_active>\S+)\s+"
     r"failsafe=(?P<failsafe>\S+)\s+"
     r"mode=(?P<mode>.+?)\s+sensors=\[(?P<sensors>.*)\]"
@@ -52,19 +53,76 @@ STATUS_RE = re.compile(
 SENSOR_RE = re.compile(r"ch(\d+):([\d.]+)C/(\d+)%|ch(\d+):ERR")
 
 AUTOTUNE_MODE_RE = re.compile(
-    r"autotune/(?P<phase>\w+) (?P<elapsed>\d+)s (?P<cycles>\d+/\d+)cyc pre>=(?P<pre>\d+)C"
+    r"autotune/(?P<phase>[\w-]+) (?P<elapsed>\d+)s (?P<cycles>\d+/\d+)cyc pre>=(?P<pre>\d+)C"
 )
 
+FANCHARS_MODE_RE = re.compile(
+    r"fanchars/(?P<phase>[\w-]+) (?P<elapsed>\d+)s run (?P<run>[\w]+)/(?P<runs>\d+) "
+    r"fan=(?P<testfan>\d+) heat=(?P<heat>\d+)%"
+)
 
-def format_mode_line(mode: str) -> str:
+FANCHARS_PHASE_HELP: dict[str, str] = {
+    "precool": "Cooling chamber to 40 C avg before first fan test (fan at 100% now)",
+    "cool": "Cooling to 40 C avg before next fan test (fan at 100% now)",
+    "heat": "Heating to 60 C max corner at test fan speed",
+    "hold": "Holding at max — measuring temperature spread",
+    "refine": "Refine run — midpoint PWM between two best spreads",
+}
+
+
+def fan_pct_from_pwm(pwm: int) -> int:
+    return (pwm * 100) // 255
+
+
+def format_fan_display(fan_raw: str) -> str:
+    match = re.match(r"(\d+)/255\((\d+)%\)(.*)$", fan_raw.strip())
+    if not match:
+        return fan_raw
+    suffix = match.group(3).strip()
+    pct = match.group(2)
+    if suffix:
+        return f"{pct}% {suffix}"
+    return f"{pct}%"
+
+
+def format_mode_line(mode: str, avg: str = "") -> tuple[str, str]:
+    """Return (mode summary, activity detail) for the dashboard."""
     match = AUTOTUNE_MODE_RE.match(mode)
     if match:
         d = match.groupdict()
-        return (
-            f"Autotune {d['phase']}: {d['elapsed']}s elapsed, "
+        summary = (
+            f"Autotune {d['phase']}: {d['elapsed']}s, "
             f"{d['cycles']} cycles, preheat avg >= {d['pre']} C"
         )
-    return f"Mode: {mode}"
+        return summary, "Relay tuning heat PI — heater bang-bang around setpoint"
+
+    match = FANCHARS_MODE_RE.match(mode)
+    if match:
+        d = match.groupdict()
+        phase = d["phase"]
+        test_pct = fan_pct_from_pwm(int(d["testfan"]))
+        run = d["run"]
+        runs = d["runs"]
+        if run == "pre":
+            run_text = f"preparing (before 1/{runs})"
+        elif run.startswith("n"):
+            run_text = f"before {run[1:]}/{runs} ({test_pct}% fan next)"
+        elif run == "refine":
+            run_text = f"refine ({test_pct}% fan)"
+        else:
+            run_text = f"{run}/{runs} ({test_pct}% fan)"
+        summary = f"Fan chars {phase}: {d['elapsed']}s — {run_text}"
+        detail = FANCHARS_PHASE_HELP.get(phase, "")
+        if phase in ("precool", "cool") and avg not in ("—", ""):
+            try:
+                detail += f" — avg {avg} C"
+            except ValueError:
+                pass
+        return summary, detail
+
+    if mode in ("manual", "regulating"):
+        return f"Mode: {mode}", "Normal temperature control"
+    return f"Mode: {mode}", ""
 
 
 @dataclass
@@ -85,8 +143,9 @@ class DryerState:
     cutoff_active: str = "no"
     failsafe: str = "no"
     mode: str = "—"
+    activity: str = ""
     sensors: list[tuple[str, str, str]] = field(default_factory=list)
-    messages: deque[str] = field(default_factory=lambda: deque(maxlen=12))
+    messages: deque[str] = field(default_factory=lambda: deque(maxlen=24))
     csv_logging: bool = False
     csv_path: Path | None = None
     port: str = ""
@@ -139,13 +198,20 @@ def apply_status(state: DryerState, data: dict) -> None:
     state.hblk = data["hblk"]
     state.ssr = data["ssr"]
     fan_raw = data["fan"]
-    state.fan = fan_raw
+    state.fan = format_fan_display(fan_raw)
     state.fan_note = ""
-    if fan_raw.endswith("(off)") or fan_raw.endswith("(cooldown)") or " TEST" in fan_raw:
+    if "(off)" in fan_raw or "(cooldown)" in fan_raw:
         state.fan_note = fan_raw[fan_raw.find("(") :] if "(" in fan_raw else ""
+    elif "(manual)" in fan_raw or "(stir)" in fan_raw:
+        state.fan_note = fan_raw[fan_raw.find("(") :] if "(" in fan_raw else ""
+    elif "(fanchars-" in fan_raw:
+        state.fan_note = fan_raw[fan_raw.find("(fanchars-") :]
     state.cutoff_active = data["cutoff_active"]
     state.failsafe = data["failsafe"]
     state.mode = data["mode"]
+    summary, activity = format_mode_line(data["mode"], data["avg"])
+    state.mode = summary
+    state.activity = activity
     state.sensors = data["sensor_list"]
 
 
@@ -155,8 +221,7 @@ class SerialWorker:
         self.state = state
         self.lock = lock
         self.stop = threading.Event()
-        self._log_fh = None
-        self._header_written = [False]
+        self._csv: CsvSession | None = None
         self._thread: threading.Thread | None = None
 
     def start(self) -> None:
@@ -171,9 +236,9 @@ class SerialWorker:
         self.stop.set()
         if self._thread is not None:
             self._thread.join(timeout=1.5)
-        if self._log_fh is not None:
-            self._log_fh.close()
-            self._log_fh = None
+        if self._csv is not None:
+            self._csv.close()
+            self._csv = None
 
     def send(self, command: str) -> None:
         if self.ser is None:
@@ -186,19 +251,21 @@ class SerialWorker:
             if enabled and not self.state.csv_logging:
                 log_dir.mkdir(parents=True, exist_ok=True)
                 path = log_dir / f"dryer_{datetime.now():%Y%m%d_%H%M%S}.csv"
-                self._log_fh = path.open("w", encoding="utf-8")
-                self._header_written = [False]
+                self._csv = CsvSession(path)
                 self.state.csv_path = path
                 self.state.csv_logging = True
-                self.state.messages.append(f"CSV -> {path.name}")
+                self.state.messages.append(f"CSV -> {path.name} (on status)")
                 self.send("log on")
             elif not enabled and self.state.csv_logging:
                 self.send("log off")
                 self.state.csv_logging = False
                 self.state.csv_path = None
-                if self._log_fh is not None:
-                    self._log_fh.close()
-                    self._log_fh = None
+                if self._csv is not None:
+                    rows = self._csv.row_count
+                    self._csv.close()
+                    self._csv = None
+                    self.state.messages.append(f"CSV logging off ({rows} rows)")
+                else:
                     self.state.messages.append("CSV logging off")
 
     def _note(self, line: str) -> None:
@@ -220,15 +287,19 @@ class SerialWorker:
             if not line:
                 continue
 
+            if line.startswith("fanchars:"):
+                self._note(line)
+                continue
+
             if line.startswith("csv,") or line.startswith("csv_hdr,"):
-                if self._log_fh is not None:
-                    write_csv_row(self._log_fh, line, self._header_written)
                 continue
 
             parsed = parse_status(line)
             if parsed:
                 with self.lock:
                     apply_status(self.state, parsed)
+                if self._csv is not None:
+                    self._csv.write_status(parsed)
                 continue
 
             if line.startswith("target="):
@@ -335,8 +406,8 @@ def _preset_menu(stdscr, worker: SerialWorker) -> None:
 def _draw_dashboard(stdscr, state: DryerState) -> None:
     stdscr.erase()
     height, width = stdscr.getmaxyx()
-    if height < 19 or width < 60:
-        _safe_addstr(stdscr, 0, 0, "Terminal too small (need 60x19).")
+    if height < 20 or width < 60:
+        _safe_addstr(stdscr, 0, 0, "Terminal too small (need 60x20).")
         stdscr.refresh()
         return
 
@@ -349,14 +420,19 @@ def _draw_dashboard(stdscr, state: DryerState) -> None:
     _safe_addstr(stdscr, row, 36, f"Trip: {state.cutoff_active}", cutoff_attr)
 
     row += 1
-    mode_text = format_mode_line(state.mode)
+    mode_text = state.mode
     _safe_addstr(stdscr, row, 2, f"{mode_text[: max(0, width - 18)]}  FS: {state.failsafe}")
 
     row += 1
+    if state.activity:
+        _safe_addstr(stdscr, row, 2, state.activity[: max(0, width - 4)], curses.A_DIM)
+        row += 1
     _safe_addstr(stdscr, row, 2, f"Avg: {state.avg} C   Min: {state.min_temp} C   Max: {state.max_temp} C   Spread: {state.spread} C")
 
     row += 1
-    fan_text = state.fan if state.fan_note == "" else state.fan
+    fan_text = state.fan
+    if state.fan_note and "(fanchars-" not in state.fan_note:
+        fan_text = f"{state.fan} {state.fan_note}"
     _safe_addstr(
         stdscr,
         row,
@@ -408,7 +484,7 @@ def _draw_dashboard(stdscr, state: DryerState) -> None:
         stdscr,
         help_y,
         1,
-        "0 idle | t target | p presets | f fan | l log | a autotune | : cmd | q quit",
+        "0 idle | t target | p presets | f fan | l log | a autotune | c fanchars | : cmd | q quit",
         curses.A_DIM,
     )
     stdscr.refresh()
@@ -428,6 +504,8 @@ def _curses_main(stdscr, ser, log_dir: Path, auto_log_on: bool) -> int:
     worker = SerialWorker(ser, state, lock)
     worker.start()
     worker.send("status")
+    time.sleep(0.4)
+    worker.send("status")
     if auto_log_on:
         worker.set_csv_logging(True, log_dir)
 
@@ -451,8 +529,9 @@ def _curses_main(stdscr, ser, log_dir: Path, auto_log_on: bool) -> int:
                     cutoff_active=state.cutoff_active,
                     failsafe=state.failsafe,
                     mode=state.mode,
+                    activity=state.activity,
                     sensors=list(state.sensors),
-                    messages=deque(state.messages, maxlen=12),
+                    messages=deque(state.messages, maxlen=24),
                     csv_logging=state.csv_logging,
                     csv_path=state.csv_path,
                     port=state.port,
@@ -490,6 +569,9 @@ def _curses_main(stdscr, ser, log_dir: Path, auto_log_on: bool) -> int:
                 if value is not None:
                     cmd = "autotune" if value == "" else f"autotune {value}"
                     worker.send(cmd)
+            elif key == ord("c"):
+                worker.send("fanchars")
+                worker._note("Started fanchars — 30/100/60/80% then refine if needed")
             elif key == ord(":"):
                 value = _prompt(stdscr, "Command")
                 if value is not None and value != "":

scripts/fan_characterize.py

@@ -0,0 +1,187 @@
+#!/usr/bin/env python3
+"""Run fan characterize sweep and capture fc,... serial log lines to CSV.
+
+Each profile heats from ~35 C avg to max corner (default 60 C) at a fixed fan
+PWM, measures spread during a hold, cools, then repeats for the next speed.
+Firmware prints the best fan at the end; use fanchars save on the device.
+
+Example:
+  ./fan_characterize.py
+  ./fan_characterize.py -o logs/fanchars.csv
+"""
+
+from __future__ import annotations
+
+import argparse
+import re
+import sys
+import time
+from collections import defaultdict
+from datetime import datetime, timezone
+from pathlib import Path
+
+from capture_csv import decode_line, open_serial, resolve_port
+
+FC_RE = re.compile(
+    r"^fc,(?P<ms>\d+),(?P<phase>\w+),(?P<run>\d+/\d+),"
+    r"(?P<fan>\d+),(?P<heater>\d+),"
+    r"(?P<avg>[\d.]+),(?P<min>[\d.]+),(?P<max>[\d.]+),(?P<spread>[\d.]+)"
+    r"(?:,(?P<temps>.*))?$"
+)
+DONE_RE = re.compile(r"^fanchars: done")
+FAIL_RE = re.compile(r"^fanchars: abort")
+RUN_SUMMARY_RE = re.compile(r"^fanchars: f=(?P<fan>\d+) spr=(?P<mean>[\d.]+)")
+BEST_RE = re.compile(r"^  best (?P<fan>\d+) spr=(?P<mean>[\d.]+)")
+
+HEADER = (
+    "wall_time,ms,phase,run,fan_pwm,fan_pct,heater_pct,avg_c,min_c,max_c,spread_c,"
+    "ch2_t,ch3_t,ch4_t,ch5_t"
+)
+
+
+def fan_pct(pwm: int) -> int:
+    return (pwm * 100) // 255
+
+
+def send_command(ser, command: str, timeout: float = 3.0) -> list[str]:
+    ser.write((command.strip() + "\n").encode("utf-8"))
+    ser.flush()
+    lines: list[str] = []
+    deadline = time.monotonic() + timeout
+    while time.monotonic() < deadline:
+        raw = ser.readline()
+        if not raw:
+            continue
+        line = decode_line(raw)
+        if not line:
+            continue
+        lines.append(line)
+        if line.startswith("OK ") or line.startswith("ERR "):
+            break
+    return lines
+
+
+def parse_fc_line(line: str) -> dict | None:
+    match = FC_RE.match(line)
+    if not match:
+        return None
+    data = match.groupdict()
+    temps = data.pop("temps") or ""
+    channels = (temps.split(",") + ["", "", "", ""])[:4]
+    data["ch2_t"], data["ch3_t"], data["ch4_t"], data["ch5_t"] = channels
+    data["fan_pwm"] = data.pop("fan")
+    data["heater_pct"] = data.pop("heater")
+    return data
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description="Capture fan characterize sweep")
+    parser.add_argument("-p", "--port", help="Serial port (default: auto-detect)")
+    parser.add_argument("-b", "--baud", type=int, default=115200)
+    parser.add_argument("--max", type=float, default=60.0, help="Max corner temp (C, default 60)")
+    parser.add_argument(
+        "-o",
+        "--output",
+        type=Path,
+        help="Output CSV (default: logs/fanchars_YYYYMMDD_HHMMSS.csv)",
+    )
+    parser.add_argument(
+        "--timeout",
+        type=float,
+        default=5 * 3600,
+        help="Abort if not done within this many seconds (default: 5 h)",
+    )
+    args = parser.parse_args()
+
+    out = args.output
+    if out is None:
+        out = Path("logs") / f"fanchars_{datetime.now():%Y%m%d_%H%M%S}.csv"
+    out.parent.mkdir(parents=True, exist_ok=True)
+
+    cmd = f"fanchars {args.max:g}" if args.max != 60.0 else "fanchars"
+    print(f"Command: {cmd}", file=sys.stderr)
+    print(f"Output: {out}", file=sys.stderr)
+    print("Expect heat/cool cycles per fan speed. Ctrl+C sends fanchars stop.", file=sys.stderr)
+
+    port = resolve_port(args.port)
+    run_means: dict[int, float] = {}
+    best_line = ""
+
+    try:
+        with open_serial(port, args.baud) as ser:
+            time.sleep(0.3)
+            while ser.in_waiting:
+                decode_line(ser.readline())
+
+            lines = send_command(ser, cmd, timeout=5.0)
+            for line in lines:
+                print(line, file=sys.stderr)
+                if line.startswith("ERR "):
+                    return 1
+
+            send_command(ser, "log on", timeout=2.0)
+
+            with out.open("w", encoding="utf-8") as fh:
+                fh.write(HEADER + "\n")
+                deadline = time.monotonic() + args.timeout
+                while time.monotonic() < deadline:
+                    raw = ser.readline()
+                    if not raw:
+                        continue
+                    line = decode_line(raw)
+                    if not line:
+                        continue
+
+                    row = parse_fc_line(line)
+                    if row:
+                        wall = datetime.now(timezone.utc).isoformat()
+                        fh.write(
+                            f"{wall},{row['ms']},{row['phase']},{row['run']},"
+                            f"{row['fan_pwm']},{fan_pct(int(row['fan_pwm']))},"
+                            f"{row['heater_pct']},{row['avg']},{row['min']},{row['max']},"
+                            f"{row['spread']},{row['ch2_t']},{row['ch3_t']},"
+                            f"{row['ch4_t']},{row['ch5_t']}\n"
+                        )
+                        fh.flush()
+
+                    match = RUN_SUMMARY_RE.match(line)
+                    if match:
+                        run_means[int(match.group("fan"))] = float(match.group("mean"))
+                        print(line, file=sys.stderr)
+
+                    if BEST_RE.search(line):
+                        best_line = line.strip()
+
+                    if DONE_RE.search(line) or FAIL_RE.search(line):
+                        print(line, file=sys.stderr)
+                        break
+                else:
+                    print("Timeout waiting for fanchars to finish", file=sys.stderr)
+                    return 1
+
+            if best_line:
+                print(best_line, file=sys.stderr)
+                print("Run: fanchars save  (on device) to store stir PWM", file=sys.stderr)
+            elif run_means:
+                best_fan = min(run_means, key=run_means.get)
+                print(
+                    f"Best from logs: fan {best_fan} ({fan_pct(best_fan)}%) "
+                    f"mean spread {run_means[best_fan]:.2f} C",
+                    file=sys.stderr,
+                )
+
+    except KeyboardInterrupt:
+        print("\nStopping…", file=sys.stderr)
+        try:
+            with open_serial(port, args.baud) as ser:
+                send_command(ser, "fanchars stop")
+        except OSError:
+            pass
+        return 130
+
+    print(f"Wrote {out}", file=sys.stderr)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

scripts/fan_test.py

@@ -0,0 +1,147 @@
+#!/usr/bin/env python3
+"""Cycle fan speeds on the dryer for wiring / PWM verification.
+
+Uses the firmware `fan test <pwm>` command (heater stays off). Sends `target 0`
+first so the thermal loop is idle.
+
+Example:
+  ./fan_test.py
+  ./fan_test.py --pct 30 50 100 --interval 3 --loop
+"""
+
+from __future__ import annotations
+
+import argparse
+import re
+import sys
+import time
+
+from capture_csv import decode_line, open_serial, resolve_port
+
+OK_RE = re.compile(r"^OK ")
+ERR_RE = re.compile(r"^ERR ")
+FAN_STATUS_RE = re.compile(r"fan=(\d+)/255\((\d+)%\)")
+
+
+def pct_to_pwm(pct: int) -> int:
+    if pct < 0 or pct > 100:
+        raise ValueError(f"fan percent must be 0-100, got {pct}")
+    return round(pct * 255 / 100)
+
+
+def send_command(ser, command: str, timeout: float = 2.0) -> list[str]:
+    ser.write((command.strip() + "\n").encode("utf-8"))
+    ser.flush()
+    lines: list[str] = []
+    deadline = time.monotonic() + timeout
+    while time.monotonic() < deadline:
+        raw = ser.readline()
+        if not raw:
+            continue
+        line = decode_line(raw)
+        if not line:
+            continue
+        lines.append(line)
+        if OK_RE.match(line) or ERR_RE.match(line):
+            break
+    return lines
+
+
+def drain_status(ser, duration: float) -> str | None:
+    """Read serial for `duration` seconds; return last status fan field if seen."""
+    fan_field: str | None = None
+    deadline = time.monotonic() + duration
+    while time.monotonic() < deadline:
+        raw = ser.readline()
+        if not raw:
+            continue
+        line = decode_line(raw)
+        if not line or line.startswith("csv"):
+            continue
+        match = FAN_STATUS_RE.search(line)
+        if match:
+            fan_field = f"{match.group(1)}/255 ({match.group(2)}%)"
+        elif line.startswith("target="):
+            print(f"  status: {line}", flush=True)
+    return fan_field
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description="Cycle fan PWM to verify fan control")
+    parser.add_argument(
+        "-p",
+        "--port",
+        help="Serial port (default: auto-detect)",
+    )
+    parser.add_argument("-b", "--baud", type=int, default=115200)
+    parser.add_argument(
+        "--pct",
+        type=int,
+        nargs="+",
+        default=[0, 30, 100, 200, 255],
+        metavar="PCT",
+        help="Fan speeds in percent (default: 0 30 100 200 255)",
+    )
+    parser.add_argument(
+        "--interval",
+        type=float,
+        default=5.0,
+        metavar="SEC",
+        help="Seconds to hold each step (default: 5)",
+    )
+    parser.add_argument(
+        "--loop",
+        action="store_true",
+        help="Repeat the sequence until Ctrl+C",
+    )
+    args = parser.parse_args()
+
+    port = resolve_port(args.port)
+    sequence = [(pct, pct_to_pwm(pct)) for pct in args.pct]
+
+    print(f"Port: {port}", file=sys.stderr)
+    print(
+        f"Sequence: {' -> '.join(str(p) + '%' for p, _ in sequence)} "
+        f"every {args.interval:g}s (heater off)",
+        file=sys.stderr,
+    )
+    print("Ctrl+C to stop\n", file=sys.stderr)
+
+    interrupted = False
+    with open_serial(port, args.baud) as ser:
+        ser.reset_input_buffer()
+
+        lines = send_command(ser, "target 0")
+        for line in lines:
+            print(line, flush=True)
+        if any(ERR_RE.match(line) for line in lines):
+            return 1
+
+        try:
+            while True:
+                for pct, pwm in sequence:
+                    print(f">>> fan test {pwm}  ({pct}%)", flush=True)
+                    lines = send_command(ser, f"fan test {pwm}")
+                    for line in lines:
+                        print(f"    {line}", flush=True)
+                    if any(ERR_RE.match(line) for line in lines):
+                        return 1
+
+                    reported = drain_status(ser, args.interval)
+                    if reported:
+                        print(f"    reported fan={reported}", flush=True)
+
+                if not args.loop:
+                    break
+        except KeyboardInterrupt:
+            interrupted = True
+            print("\nInterrupted", file=sys.stderr)
+        finally:
+            print(">>> fan test 0 (stop)", flush=True)
+            send_command(ser, "fan test 0")
+
+    return 130 if interrupted else 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

scripts/plot_logs.py

@@ -0,0 +1,232 @@
+#!/usr/bin/env python3
+"""Plot dryer CSV logs from capture_csv.py, the TUI, or firmware `log on`.
+
+Example:
+  python3 scripts/plot_logs.py logs/dryer_20260707_195354.csv
+  python3 scripts/plot_logs.py logs/          # newest .csv in directory
+  python3 scripts/plot_logs.py remote         # newest .csv on alex@10.81.16.44
+  python3 scripts/plot_logs.py logs/foo.csv -o plot.png
+"""
+
+from __future__ import annotations
+
+import argparse
+import csv
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+REMOTE_SSH = "alex@10.81.16.44"
+REMOTE_LOG_DIRS = (
+    "~/arduino-filament-dryer/logs",
+    "~/voron-filament-dryer/logs",
+    "~/logs",
+)
+
+
+def import_matplotlib():
+    try:
+        import matplotlib.pyplot as plt
+    except ImportError:
+        print("Install matplotlib: pip install matplotlib", file=sys.stderr)
+        raise SystemExit(1) from None
+    return plt
+
+
+def fetch_remote_csv(remote_dirs: tuple[str, ...] = REMOTE_LOG_DIRS) -> Path:
+    dir_list = " ".join(remote_dirs)
+    find_cmd = (
+        f"for d in {dir_list}; do "
+        'if [ -d "$d" ]; then ls -t "$d"/*.csv 2>/dev/null; fi; done | head -1'
+    )
+    result = subprocess.run(
+        ["ssh", REMOTE_SSH, find_cmd],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+    remote_path = result.stdout.strip()
+    if result.returncode != 0 or not remote_path:
+        err = result.stderr.strip()
+        print(f"No remote CSV found on {REMOTE_SSH}", file=sys.stderr)
+        if err:
+            print(err, file=sys.stderr)
+        raise SystemExit(1)
+
+    local_path = Path(tempfile.gettempdir()) / f"dryer_remote_{Path(remote_path).name}"
+    scp = subprocess.run(
+        ["scp", f"{REMOTE_SSH}:{remote_path}", str(local_path)],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+    if scp.returncode != 0:
+        print(f"scp failed for {REMOTE_SSH}:{remote_path}", file=sys.stderr)
+        if scp.stderr.strip():
+            print(scp.stderr.strip(), file=sys.stderr)
+        raise SystemExit(1)
+
+    print(f"Fetched {REMOTE_SSH}:{remote_path}", file=sys.stderr)
+    return local_path
+
+
+def resolve_csv(path: Path) -> Path:
+    if path.is_dir():
+        matches = sorted(path.glob("*.csv"), key=lambda p: p.stat().st_mtime, reverse=True)
+        if not matches:
+            print(f"No CSV files in {path}", file=sys.stderr)
+            raise SystemExit(1)
+        return matches[0]
+    if not path.is_file():
+        print(f"Not found: {path}", file=sys.stderr)
+        raise SystemExit(1)
+    return path
+
+
+def load_rows(path: Path) -> tuple[list[str], list[dict[str, str]]]:
+    with path.open(newline="", encoding="utf-8") as fh:
+        reader = csv.DictReader(fh)
+        if reader.fieldnames is None:
+            print(f"Empty CSV: {path}", file=sys.stderr)
+            raise SystemExit(1)
+        rows = list(reader)
+    return list(reader.fieldnames), rows
+
+
+def column_float(rows: list[dict[str, str]], name: str) -> list[float | None]:
+    out: list[float | None] = []
+    for row in rows:
+        raw = row.get(name, "").strip()
+        if not raw:
+            out.append(None)
+            continue
+        try:
+            out.append(float(raw))
+        except ValueError:
+            out.append(None)
+    return out
+
+
+def time_axis(rows: list[dict[str, str]], fieldnames: list[str]) -> tuple[list[float], str]:
+    if "ms" in fieldnames:
+        ms = column_float(rows, "ms")
+        if any(v is not None for v in ms):
+            t0 = next(v for v in ms if v is not None)
+            return [((v or t0) - t0) / 60000.0 for v in ms], "minutes since start"
+
+    if "wall_time" in fieldnames:
+        from datetime import datetime
+
+        times: list[float] = []
+        parsed: list[datetime] = []
+        for row in rows:
+            raw = row.get("wall_time", "").strip()
+            if not raw:
+                continue
+            try:
+                parsed.append(datetime.fromisoformat(raw))
+            except ValueError:
+                continue
+        if parsed:
+            t0 = parsed[0]
+            for dt in parsed:
+                times.append((dt - t0).total_seconds() / 60.0)
+            return times, "minutes since start"
+
+    return [float(i) for i in range(len(rows))], "sample"
+
+
+def plot_csv(path: Path, output: Path | None, title: str | None = None) -> None:
+    plt = import_matplotlib()
+
+    fieldnames, rows = load_rows(path)
+    if not rows:
+        print(f"No data rows in {path}", file=sys.stderr)
+        raise SystemExit(1)
+
+    x, x_label = time_axis(rows, fieldnames)
+    if len(x) != len(rows):
+        x = [float(i) for i in range(len(rows))]
+        x_label = "sample"
+
+    fig, axes = plt.subplots(3, 1, figsize=(11, 8), sharex=True, constrained_layout=True)
+    fig.suptitle(title or path.name)
+
+    temp_ax = axes[0]
+    for col, label, style in (
+        ("avg_c", "avg", "-"),
+        ("min_c", "min", "--"),
+        ("max_c", "max", "--"),
+        ("target_c", "target", ":"),
+    ):
+        if col not in fieldnames:
+            continue
+        y = column_float(rows, col)
+        temp_ax.plot(x, y, style, label=label, linewidth=1.5 if col == "avg_c" else 1.0)
+    for ch in (2, 3, 4, 5):
+        col = f"ch{ch}_t"
+        if col in fieldnames:
+            y = column_float(rows, col)
+            temp_ax.plot(x, y, "-", alpha=0.35, linewidth=0.8, label=f"ch{ch}")
+    temp_ax.set_ylabel("°C")
+    temp_ax.legend(loc="upper left", ncol=4, fontsize=8)
+    temp_ax.grid(True, alpha=0.3)
+
+    duty_ax = axes[1]
+    if "heater_pct" in fieldnames:
+        duty_ax.plot(x, column_float(rows, "heater_pct"), "C1-", label="heater %")
+    if "heatlim_pct" in fieldnames:
+        duty_ax.plot(x, column_float(rows, "heatlim_pct"), "C1--", alpha=0.6, label="heatlim %")
+    if "fan_pct" in fieldnames:
+        duty_ax.plot(x, column_float(rows, "fan_pct"), "C0-", label="fan %")
+    duty_ax.set_ylabel("%")
+    duty_ax.legend(loc="upper left", fontsize=8)
+    duty_ax.grid(True, alpha=0.3)
+
+    spread_ax = axes[2]
+    if "spread_c" in fieldnames:
+        spread_ax.plot(x, column_float(rows, "spread_c"), "C2-", label="spread")
+    spread_ax.set_ylabel("°C")
+    spread_ax.set_xlabel(x_label)
+    spread_ax.legend(loc="upper left", fontsize=8)
+    spread_ax.grid(True, alpha=0.3)
+
+    if output is not None:
+        fig.savefig(output, dpi=150)
+        print(f"Wrote {output}")
+    else:
+        plt.show()
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(description="Plot dryer CSV temperature logs")
+    parser.add_argument(
+        "csv",
+        help='CSV file, directory (newest .csv), or "remote" for newest on ' + REMOTE_SSH,
+    )
+    parser.add_argument("-o", "--output", type=Path, help="Save PNG instead of opening a window")
+    parser.add_argument(
+        "--remote-dir",
+        action="append",
+        metavar="DIR",
+        help=f"Remote log directory on {REMOTE_SSH} (repeatable; used with remote)",
+    )
+    args = parser.parse_args(argv)
+
+    plot_title: str | None = None
+    if args.csv == "remote":
+        remote_dirs = tuple(args.remote_dir) if args.remote_dir else REMOTE_LOG_DIRS
+        path = fetch_remote_csv(remote_dirs)
+        plot_title = f"{REMOTE_SSH}:{path.name}"
+    else:
+        path = resolve_csv(Path(args.csv))
+
+    if args.output is None:
+        print(f"Plotting {plot_title or path}", file=sys.stderr)
+    plot_csv(path, args.output, title=plot_title)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

scripts/requirements.txt

@@ -1 +1,2 @@
 pyserial>=3.5
+matplotlib>=3.8

src/fan_characterize.cpp

@@ -0,0 +1,354 @@
+#include "fan_characterize.h"
+
+FanCharacterize::FanCharacterize()
+    : phase_(Phase::Idle),
+      maxCornerC_(FANCHARS_MAX_CORNER_C),
+      coolAvgC_(FANCHARS_COOL_AVG_C),
+      heaterPct_(FANCHARS_HEATER_PCT),
+      profileIndex_(0),
+      refineFanPwm_(0),
+      refineRun_(false),
+      sessionStartMs_(0),
+      phaseStartMs_(0),
+      lastLogMs_(0),
+      spreadSum_(0.0f),
+      spreadSamples_(0),
+      resultCount_(0),
+      winnerFanPwm_(0) {}
+
+bool FanCharacterize::isActive() const {
+  return phase_ == Phase::Precool || phase_ == Phase::Heat || phase_ == Phase::Hold ||
+         phase_ == Phase::Cooldown;
+}
+
+uint32_t FanCharacterize::elapsedMs(uint32_t nowMs) const {
+  if (sessionStartMs_ == 0) {
+    return 0;
+  }
+  return nowMs - sessionStartMs_;
+}
+
+uint8_t FanCharacterize::currentFanPwm() const {
+  if (profileIndex_ >= FANCHARS_COARSE_COUNT) {
+    return refineFanPwm_;
+  }
+  return FANCHARS_COARSE_PWM[profileIndex_];
+}
+
+const char *FanCharacterize::phaseName() const {
+  if (isRefineRun() && (phase_ == Phase::Heat || phase_ == Phase::Hold)) {
+    return "refine";
+  }
+  switch (phase_) {
+  case Phase::Precool:
+    return "precool";
+  case Phase::Heat:
+    return "heat";
+  case Phase::Hold:
+    return "hold";
+  case Phase::Cooldown:
+    return "cool";
+  default:
+    return "";
+  }
+}
+
+bool FanCharacterize::start(float maxCornerC, float avgTempC) {
+  if (maxCornerC < 45.0f || maxCornerC > EMERGENCY_ABSOLUTE_MAX_C - 5.0f) {
+    return false;
+  }
+
+  maxCornerC_ = maxCornerC;
+  heaterPct_ = FANCHARS_HEATER_PCT;
+  profileIndex_ = 0;
+  refineFanPwm_ = 0;
+  refineRun_ = false;
+  resultCount_ = 0;
+  winnerFanPwm_ = 0;
+  sessionStartMs_ = millis();
+  phaseStartMs_ = sessionStartMs_;
+  lastLogMs_ = 0;
+  resetProfileStats();
+
+  phase_ = avgTempC > coolAvgC_ + FANCHARS_PRECOOL_MARGIN_C ? Phase::Precool : Phase::Heat;
+
+  Serial.print(F("fanchars: "));
+  Serial.print(FANCHARS_COARSE_COUNT);
+  Serial.print(F(" fans + refine h="));
+  Serial.println(heaterPct_, 0);
+  return true;
+}
+
+void FanCharacterize::abort() {
+  if (isActive()) {
+    Serial.println(F("fanchars: stop"));
+  }
+  phase_ = Phase::Idle;
+  sessionStartMs_ = 0;
+}
+
+void FanCharacterize::reset() {
+  phase_ = Phase::Idle;
+  sessionStartMs_ = 0;
+}
+
+bool FanCharacterize::update(float avgTempC, float maxTempC, float spreadC, uint32_t nowMs,
+                             float &heaterDutyOut, uint8_t &fanPwmOut) {
+  heaterDutyOut = 0.0f;
+  fanPwmOut = 0;
+
+  if (phase_ == Phase::Idle || phase_ == Phase::Done || phase_ == Phase::Failed) {
+    return false;
+  }
+
+  if (maxTempC >= EMERGENCY_ABSOLUTE_MAX_C) {
+    fail(F("fanchars: abort limit"));
+    return false;
+  }
+
+  if (phase_ == Phase::Precool) {
+    fanPwmOut = FAN_MAX_PWM;
+    if (nowMs - phaseStartMs_ > FANCHARS_COOLDOWN_TIMEOUT_MS) {
+      fail(F("fanchars: abort precool"));
+      return false;
+    }
+    if (avgTempC <= coolAvgC_) {
+      beginProfileHeat(nowMs);
+    }
+    return true;
+  }
+
+  if (phase_ == Phase::Heat) {
+    fanPwmOut = currentFanPwm();
+    heaterDutyOut = heaterPct_;
+    if (nowMs - phaseStartMs_ > FANCHARS_HEAT_TIMEOUT_MS) {
+      skipProfile(nowMs, maxTempC);
+      return true;
+    }
+    if (maxTempC >= maxCornerC_) {
+      enterHold(nowMs);
+    }
+    return true;
+  }
+
+  if (phase_ == Phase::Hold) {
+    fanPwmOut = currentFanPwm();
+    spreadSum_ += spreadC;
+    ++spreadSamples_;
+    if (nowMs - phaseStartMs_ >= FANCHARS_HOLD_MS) {
+      finishProfile(nowMs);
+    }
+    return true;
+  }
+
+  if (phase_ == Phase::Cooldown) {
+    fanPwmOut = FAN_MAX_PWM;
+    if (nowMs - phaseStartMs_ > FANCHARS_COOLDOWN_TIMEOUT_MS) {
+      fail(F("fanchars: abort cool"));
+      return false;
+    }
+    if (avgTempC <= coolAvgC_) {
+      beginProfileHeat(nowMs);
+    }
+    return true;
+  }
+
+  return false;
+}
+
+void FanCharacterize::logIfDue(const float *sensorTemps, const bool *sensorValid, uint8_t sensorCount,
+                               float avgTempC, float minTempC, float maxTempC, float spreadC,
+                               uint32_t nowMs) {
+  if (!isActive()) {
+    return;
+  }
+  if (lastLogMs_ != 0 && nowMs - lastLogMs_ < FANCHARS_LOG_INTERVAL_MS) {
+    return;
+  }
+  lastLogMs_ = nowMs;
+
+  const uint8_t runNum =
+      profileIndex_ >= FANCHARS_COARSE_COUNT ? FANCHARS_COARSE_COUNT + 1 : profileIndex_ + 1;
+
+  Serial.print(F("fc,"));
+  Serial.print(nowMs);
+  Serial.print(',');
+  Serial.print(phaseName());
+  Serial.print(',');
+  Serial.print(runNum);
+  Serial.print('/');
+  Serial.print(FANCHARS_COARSE_COUNT + 1);
+  Serial.print(',');
+  Serial.print(currentFanPwm());
+  Serial.print(',');
+  Serial.print(heaterPct_, 0);
+  Serial.print(',');
+  Serial.print(avgTempC, 1);
+  Serial.print(',');
+  Serial.print(minTempC, 1);
+  Serial.print(',');
+  Serial.print(maxTempC, 1);
+  Serial.print(',');
+  Serial.println(spreadC, 1);
+  (void)sensorTemps;
+  (void)sensorValid;
+  (void)sensorCount;
+}
+
+void FanCharacterize::resetProfileStats() {
+  spreadSum_ = 0.0f;
+  spreadSamples_ = 0;
+}
+
+void FanCharacterize::beginProfileHeat(uint32_t nowMs) {
+  phase_ = Phase::Heat;
+  phaseStartMs_ = nowMs;
+  resetProfileStats();
+  Serial.print(F("fanchars: f="));
+  Serial.println(currentFanPwm());
+}
+
+void FanCharacterize::enterHold(uint32_t nowMs) {
+  phase_ = Phase::Hold;
+  phaseStartMs_ = nowMs;
+  resetProfileStats();
+}
+
+void FanCharacterize::finishProfile(uint32_t nowMs) {
+  if (spreadSamples_ == 0) {
+    fail(F("fanchars: abort hold"));
+    return;
+  }
+
+  const float meanSpread = spreadSum_ / static_cast<float>(spreadSamples_);
+  results_[resultCount_].fanPwm = currentFanPwm();
+  results_[resultCount_].meanSpreadC = meanSpread;
+  ++resultCount_;
+
+  Serial.print(F("fanchars: f="));
+  Serial.print(currentFanPwm());
+  Serial.print(F(" spr="));
+  Serial.println(meanSpread, 2);
+
+  if (isRefineRun()) {
+    finishAll(nowMs);
+    return;
+  }
+
+  if (profileIndex_ + 1 >= FANCHARS_COARSE_COUNT) {
+    planRefine(nowMs);
+    return;
+  }
+
+  ++profileIndex_;
+  phase_ = Phase::Cooldown;
+  phaseStartMs_ = nowMs;
+}
+
+void FanCharacterize::skipProfile(uint32_t nowMs, float maxTempC) {
+  Serial.print(F("fanchars: skip f="));
+  Serial.print(currentFanPwm());
+  Serial.print(F(" max="));
+  Serial.print(maxTempC, 1);
+  Serial.println(F("C"));
+
+  if (isRefineRun()) {
+    finishAll(nowMs);
+    return;
+  }
+
+  if (profileIndex_ + 1 >= FANCHARS_COARSE_COUNT) {
+    planRefine(nowMs);
+    return;
+  }
+
+  ++profileIndex_;
+  phase_ = Phase::Cooldown;
+  phaseStartMs_ = nowMs;
+}
+
+void FanCharacterize::planRefine(uint32_t nowMs) {
+  if (resultCount_ < 2) {
+    Serial.println(F("fanchars: refine skip"));
+    finishAll(nowMs);
+    return;
+  }
+
+  uint8_t bestI = 0;
+  uint8_t secondI = 1;
+  if (results_[secondI].meanSpreadC < results_[bestI].meanSpreadC) {
+    bestI = 1;
+    secondI = 0;
+  }
+  for (uint8_t i = 2; i < resultCount_; ++i) {
+    if (results_[i].meanSpreadC < results_[bestI].meanSpreadC) {
+      secondI = bestI;
+      bestI = i;
+    } else if (results_[i].meanSpreadC < results_[secondI].meanSpreadC) {
+      secondI = i;
+    }
+  }
+
+  const uint8_t bestFan = results_[bestI].fanPwm;
+  if (bestFan <= FANCHARS_LIMIT_LOW_PWM || bestFan >= FANCHARS_LIMIT_HIGH_PWM) {
+    Serial.println(F("fanchars: limit"));
+    finishAll(nowMs);
+    return;
+  }
+
+  const uint8_t secondFan = results_[secondI].fanPwm;
+  refineFanPwm_ =
+      static_cast<uint8_t>((static_cast<uint16_t>(bestFan) + secondFan) / 2);
+  if (refineFanPwm_ == bestFan || refineFanPwm_ == secondFan) {
+    finishAll(nowMs);
+    return;
+  }
+
+  refineRun_ = true;
+  profileIndex_ = FANCHARS_COARSE_COUNT;
+  phase_ = Phase::Cooldown;
+  phaseStartMs_ = nowMs;
+  Serial.print(F("fanchars: mid f="));
+  Serial.println(refineFanPwm_);
+}
+
+void FanCharacterize::finishAll(uint32_t nowMs) {
+  phase_ = Phase::Done;
+
+  if (resultCount_ == 0) {
+    winnerFanPwm_ = 0;
+    Serial.println(F("fanchars: done — no valid runs"));
+    return;
+  }
+
+  uint8_t bestIndex = 0;
+  float bestSpread = results_[0].meanSpreadC;
+  for (uint8_t i = 1; i < resultCount_; ++i) {
+    if (results_[i].meanSpreadC < bestSpread) {
+      bestSpread = results_[i].meanSpreadC;
+      bestIndex = i;
+    }
+  }
+  winnerFanPwm_ = results_[bestIndex].fanPwm;
+
+  Serial.print(F("fanchars: done "));
+  Serial.print((nowMs - sessionStartMs_) / 60000UL);
+  Serial.println(F("min"));
+  for (uint8_t i = 0; i < resultCount_; ++i) {
+    Serial.print(F("  "));
+    Serial.print(results_[i].fanPwm);
+    Serial.print(F("="));
+    Serial.println(results_[i].meanSpreadC, 2);
+  }
+  Serial.print(F("  best "));
+  Serial.print(winnerFanPwm_);
+  Serial.print(F(" spr="));
+  Serial.println(bestSpread, 2);
+  Serial.println(F("  fanchars save"));
+}
+
+void FanCharacterize::fail(const __FlashStringHelper *reason) {
+  Serial.println(reason);
+  phase_ = Phase::Failed;
+  sessionStartMs_ = 0;
+}

src/main.cpp

@@ -51,6 +51,9 @@ void readAllSensors() {
     readSensorOnChannel(SENSOR_CHANNELS[i], sensors[i]);
   }
   mux.disableAll();
+  if (Wire.getWireTimeoutFlag()) {
+    Wire.clearWireTimeoutFlag();
+  }
 }
 
 float averageValidTemperature() {
@@ -142,10 +145,18 @@ void printStatus(float avgTemp, float minTemp, float maxTemp) {
   Serial.print(F("%)"));
   if (thermal.isFanTestActive(millis())) {
     Serial.print(F(" TEST"));
+  } else if (thermal.isFanCharacterizeActive()) {
+    Serial.print(F("(fanchars-"));
+    Serial.print(thermal.fanCharacterizePhaseName());
+    Serial.print(F(")"));
   } else if (thermal.isIdle() && thermal.isFanOff()) {
     Serial.print(F("(off)"));
   } else if (thermal.isIdleCooling()) {
     Serial.print(F("(cooldown)"));
+  } else if (thermal.isFanManualOverride()) {
+    Serial.print(F("(manual)"));
+  } else if (!thermal.isIdle()) {
+    Serial.print(F("(stir)"));
   }
   Serial.print(F(" cutoff="));
   Serial.print(thermal.isCutoffActive() ? F("YES") : F("no"));
@@ -164,10 +175,32 @@ void printStatus(float avgTemp, float minTemp, float maxTemp) {
     Serial.print(F("cyc pre>="));
     Serial.print(thermal.autotunePreheatTargetC(), 0);
     Serial.print(F("C"));
-  } else if (thermal.isAdaptive()) {
-    Serial.print(F("learned"));
+  } else if (thermal.isFanCharacterizeActive()) {
+    Serial.print(F("fanchars/"));
+    Serial.print(thermal.fanCharacterizePhaseName());
+    Serial.print(F(" "));
+    Serial.print(thermal.fanCharacterizeElapsedMs(millis()) / 1000UL);
+    Serial.print(F("s run "));
+    const char *fcPhase = thermal.fanCharacterizePhaseName();
+    if (strcmp(fcPhase, "precool") == 0) {
+      Serial.print(F("pre"));
+    } else if (strcmp(fcPhase, "cool") == 0) {
+      Serial.print(F("n"));
+      Serial.print(thermal.fanCharacterizeProfileIndex() + 1);
+    } else if (thermal.isFanCharacterizeRefineRun()) {
+      Serial.print(F("refine"));
     } else {
-    Serial.print(F("manual"));
+      Serial.print(thermal.fanCharacterizeProfileIndex() + 1);
+    }
+    Serial.print(F("/"));
+    Serial.print(thermal.fanCharacterizeProfileCount());
+    Serial.print(F(" fan="));
+    Serial.print(thermal.fanCharacterizeFanPwm());
+    Serial.print(F(" heat="));
+    Serial.print(thermal.fanCharacterizeHeaterPct(), 0);
+    Serial.print(F("%"));
+  } else {
+    Serial.print(thermal.regulatingModeName());
   }
   Serial.print(F(" sensors=["));
 
@@ -196,11 +229,18 @@ void printHelp() {
   Serial.println(F("  target <C>  set target (0 = idle)"));
   Serial.println(F("  fan off     cancel idle fan override (auto-off below 40C)"));
   Serial.println(F("  fan on      idle fan 30% (optional, auto-off below 40C)"));
+  Serial.println(F("  fan auto    regulating: back to default stir fan"));
+  Serial.println(F("  fan <pwm>   regulating: manual fan override (0-255)"));
+  Serial.println(F("  fan stir    show default stir fan PWM"));
+  Serial.println(F("  fan stir N  set default stir fan + EEPROM"));
   Serial.println(F("  fan test N  set fan PWM 0-255 for 15s (verify wiring)"));
-  Serial.println(F("  autotune [C] learn PID (default: 40C when idle)"));
+  Serial.println(F("  autotune [C] learn heat PI (default: 40C when idle)"));
   Serial.println(F("  autotune stop"));
-  Serial.println(F("  pid         show PID / adaptive status"));
-  Serial.println(F("  pid default reset to factory PID"));
+  Serial.println(F("  fanchars      learn stir fan (30/100/60/80%% + refine)"));
+  Serial.println(F("  fanchars stop | fanchars save"));
+  Serial.println(F("  pid         show heat PI gains"));
+  Serial.println(F("  pid default reset heat PI to factory"));
+  Serial.println(F("  pid save    write current PI to EEPROM"));
   Serial.println(F("  status      print current readings"));
   Serial.println(F("  log on|off  CSV data stream"));
   Serial.println(F("  help        show this message"));
@@ -289,6 +329,58 @@ void processSerialLine(const char *line) {
     return;
   }
 
+  if (strcmp(line, "fan auto") == 0) {
+    if (thermal.isIdle()) {
+      Serial.println(F("ERR fan auto only when regulating (set target > 0)"));
+      return;
+    }
+    thermal.clearRegulatingFanManual();
+    Serial.print(F("OK fan stir "));
+    Serial.println(thermal.stirFanPwm());
+    return;
+  }
+
+  if (strncmp(line, "fan stir", 8) == 0) {
+    if (line[8] == '\0') {
+      Serial.print(F("stir fan PWM="));
+      Serial.println(thermal.stirFanPwm());
+      return;
+    }
+    if (line[8] == ' ') {
+      const int pwm = atoi(line + 9);
+      if (pwm < 1 || pwm > 255) {
+        Serial.println(F("ERR fan stir PWM must be 1-255"));
+        return;
+      }
+      thermal.setStirFanPwm(static_cast<uint8_t>(pwm));
+      if (!thermal.isIdle()) {
+        thermal.clearRegulatingFanManual();
+      }
+      Serial.print(F("OK stir fan "));
+      Serial.println(pwm);
+      return;
+    }
+  }
+
+  if (strncmp(line, "fan ", 4) == 0) {
+    const char *arg = line + 4;
+    if (*arg >= '0' && *arg <= '9') {
+      const int pwm = atoi(arg);
+      if (pwm < 0 || pwm > 255) {
+        Serial.println(F("ERR fan PWM must be 0-255"));
+        return;
+      }
+      if (thermal.isIdle()) {
+        Serial.println(F("ERR fan <pwm> only when regulating (or use fan test)"));
+        return;
+      }
+      thermal.setRegulatingFanManual(static_cast<uint8_t>(pwm));
+      Serial.print(F("OK fan manual "));
+      Serial.println(pwm);
+      return;
+    }
+  }
+
   if (strcmp(line, "status") == 0) {
     const float avgTemp = averageValidTemperature();
     const float minTemp = minValidTemperature();
@@ -328,6 +420,44 @@ void processSerialLine(const char *line) {
     return;
   }
 
+  if (strncmp(line, "fanchars", 8) == 0) {
+    if (strcmp(line, "fanchars stop") == 0) {
+      thermal.stopFanCharacterize();
+      Serial.println(F("OK fanchars cancelled"));
+      return;
+    }
+    if (strcmp(line, "fanchars save") == 0) {
+      if (!thermal.saveStirFanFromCharacterize()) {
+        Serial.println(F("ERR fanchars save — no completed run with winner"));
+        return;
+      }
+      Serial.println(F("OK stir fan saved"));
+      return;
+    }
+
+    float maxC = FANCHARS_MAX_CORNER_C;
+    if (line[8] == ' ') {
+      maxC = atof(line + 9);
+    }
+
+    if (maxC < 45.0f || maxC > EMERGENCY_ABSOLUTE_MAX_C - 5.0f) {
+      Serial.println(F("ERR fanchars max 45-65 C"));
+      return;
+    }
+
+    const float avgTemp = averageValidTemperature();
+    if (isnan(avgTemp)) {
+      Serial.println(F("ERR fanchars needs sensors"));
+      return;
+    }
+    if (!thermal.startFanCharacterize(maxC, avgTemp)) {
+      Serial.println(F("ERR fanchars busy"));
+      return;
+    }
+    Serial.println(F("OK fanchars started"));
+    return;
+  }
+
   if (strcmp(line, "pid") == 0 || strcmp(line, "pid show") == 0) {
     thermal.printTuning();
     return;
@@ -338,6 +468,11 @@ void processSerialLine(const char *line) {
     return;
   }
 
+  if (strcmp(line, "pid save") == 0) {
+    thermal.saveTuningToEeprom();
+    return;
+  }
+
   if (strcmp(line, "help") == 0) {
     printHelp();
     return;
@@ -389,6 +524,11 @@ void setup() {
   }
 
   Wire.begin();
+  // Without a timeout, a glitched I2C transaction (electrical noise, a
+  // momentary bad connection) can hang the AVR's Wire library forever,
+  // freezing the whole sketch. This bounds any transaction and resets the
+  // TWI hardware so the loop keeps running instead of locking up silently.
+  Wire.setWireTimeout(I2C_TIMEOUT_US, true);
 
   if (!mux.begin()) {
     Serial.println(F("ERROR: TCA9548A not found on I2C bus"));
@@ -428,6 +568,18 @@ void loop() {
 
     if (!isnan(avgTemp) && !isnan(maxTemp) && !isnan(spread)) {
       thermal.update(avgTemp, maxTemp, spread, now);
+
+      float sensorTemps[SENSOR_COUNT];
+      bool sensorValid[SENSOR_COUNT];
+      for (uint8_t i = 0; i < SENSOR_COUNT; ++i) {
+        sensorTemps[i] = sensors[i].temperatureC;
+        sensorValid[i] = sensors[i].valid;
+      }
+      const float minTemp = minValidTemperature();
+      if (thermal.isFanCharacterizeActive() && !isnan(minTemp)) {
+        thermal.logFanCharacterizeIfDue(sensorTemps, sensorValid, SENSOR_COUNT, avgTemp, minTemp,
+                                        maxTemp, spread, now);
+      }
     } else {
       thermal.enterFailSafe();
       Serial.println(F("WARN: no valid sensor readings — heater off"));