Add feature for setting arbitrary pin to arbitrary pwm over mavlink

Add flix.set_pin method for pyflix.

tools/pyflix/README.md

@@ -192,6 +192,21 @@ The following methods are in development and are not functional yet:
 
 To exit *AUTO* mode move control sticks and the drone will switch to *STAB* mode.
 
+### Additional methods
+
+You can set arbitrary output to any ESP32 pin using `set_pin` method:
+
+```python
+flix.set_pin(5, 1)  # set pin 5 to HIGH
+flix.set_pin(6, 0)  # set pin 6 to LOW
+flix.set_pin(7, 0.5)  # set pin 7 to 50% duty cycle
+flix.set_pin(8, duty=0.6, frequency=50)  # set pin 7 to 60% duty cycle at 50 Hz
+flix.set_pin(9, pwm=500, frequency=100)  # set pin 9 to 500 us pulse width at 100 Hz
+```
+
+> [!WARNING]
+> The `set_pin` method allows to set output value for almost any pin, with very few safety checks. Some configurations may lead to short circuit or other damage. Use with caution!
+
 ## Usage alongside QGroundControl
 
 You can use the Flix library alongside the QGroundControl app, using proxy mode. To do that:

tools/pyflix/flix.py

@@ -372,6 +372,17 @@ class Flix:
             raise ValueError('throttle must be in range [0, 1]')
         self.mavlink.manual_control_send(self.system_id, int(pitch * 1000), int(roll * 1000), int(throttle * 1000), int(yaw * 1000), 0)  # type: ignore
 
+    def set_pin(self, pin: int, duty: Optional[float] = None, frequency: float = 50, pwm: Optional[int] = None):
+        if frequency <= 0:
+            raise ValueError('Frequency must be positive')
+        if pwm is None:
+            if duty is None or duty < 0 or duty > 1:
+                raise ValueError('Duty cycle must be in range [0, 1]')
+            pwm = int(duty * 1000000 / frequency)
+        if pwm < 0 or pwm > 1000000 / frequency:
+            raise ValueError(f'PWM must be in range [0, {1000000 / frequency}]')
+        self.send_command(mavlink.MAV_CMD_DO_SET_SERVO, (pin, pwm, frequency, 0, 0, 0, 0))
+
     def cli(self, cmd: str, wait_response: bool = True) -> str:
         cmd = cmd.strip()
         if cmd == 'reboot':