pi without the d

README.md

@@ -82,20 +82,35 @@ 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. Tune **heat PI** (stored in EEPROM on autotune complete):
 
    ```
    target 0
-   autotune 45
+   pid default
+   autotune 50
    ```
 
-4. Start drying:
+   Emergency cutoff is fixed at **70°C** — you can autotune at 50–55°C with ABS in the chamber while hot corners stay below that.
+
+4. Tune **mix PI** (spread → fan) while drying:
 
    ```
    target 55
+   log on
    ```
 
-Send `help` over serial for all commands (`target`, `fan on/off`, `log on/off`, `status`, `pid`, etc.).
+   Watch `spread` in status. Adjust mix gains without reflash:
+
+   ```
+   mixpi 40 2
+   pid save
+   ```
+
+   Defaults: heat Kp/Ki from autotune; mix Kp=40 Ki=2 in firmware until tuned.
+
+5. Optional: `stepresp 45 35` logs open-loop fan steps if you want to estimate mix gain before live tuning.
+
+Send `help` over serial for all commands (`target`, `mixpi`, `fan test`, `log on/off`, `status`, `pid`, etc.).
 
 ## Raspberry Pi control