tunable laser diode head

thingiverse

This appears to be an Arduino sketch for a PID (Proportional-Integral-Derivative) controller, specifically designed for temperature control. I'll break down the code and explain its functionality. **Variables and Initialization** The code initializes several variables: * `r`: a scaling factor (set to 0.95) * `kP`, `kint`: PID gain values (set to 7 and 50, respectively) * `acceptable_noise`: a threshold for rejecting noise in the signal (set to 0.01) * `scale` and `offset`: constants used for scaling and offsetting the duty cycle value * `lock_center`: the target temperature (set to a value close to the actual temperature reading) * `basin`: a small value used to determine when the system is "locked" (i.e., stable) * `count`, `errorint`, `avgtemp`, `cycles_locked`, and `tt` are counters and variables used in the control loop **Setup Function** The `setup()` function initializes the Arduino: * It sets up the serial communication for printing output * It sets the pin modes for the digital outputs (LEDs) * It sets the analog write mode for the PWM output **Loop Function** The `loop()` function is where the control logic is implemented: 1. **Readings**: The code reads the temperature signal from the ADC and calculates the average value (`signal`) over a window of `smooth` samples. 2. **Calculate sigma**: It calculates the standard deviation (`sigma`) of the temperature readings using the formula: `sqrt(zz/(double)smooth-signal*signal)/signal`. 3. **PID calculation**: It calculates the error between the target temperature and the current signal, as well as the integral of this error over time (`errorint`). The PID gain values are used to calculate the duty cycle value (`dutyCycle`). 4. **Duty cycle limits**: The code checks if the calculated duty cycle is within the allowed range (between `minCycle` and `maxCycle`) and adjusts it accordingly. 5. **Reporting**: Every `num` iterations, the code prints the current state to the serial console: * `tt`: a counter for the number of times through the loop * `signal`: the current temperature reading * `lock_center`: the target temperature * `dutyCycle`: the calculated duty cycle value * `sigma`: the standard deviation of the temperature readings * `avgtemp`: the average temperature over time (not used in this code snippet) * `cycles_locked`: a counter for the number of times the system has been "locked" (i.e., stable) **Other notes** * The code uses a PID gain scheduling approach, where the gains are adjusted based on the current error and integral values. * The duty cycle is limited to prevent overheating or underheating. * The `basin` value determines when the system is considered "locked" (i.e., stable). If the absolute difference between the target temperature and the current signal is less than this value, the system is considered locked.