The first draft of a small Flask app running on Raspberry Pi to read DH-22 sensors temperature and to operate Noctua fans (A6 and A12) via GPIO PWM.

rpi_fans_app.py

import board
import atexit
import json
import adafruit_dht
import RPi.GPIO as GPIO

from flask import Flask

# Fans
FANS_PIN = 21
PWM_DEFAULT_FREQ = 100
PWM_DEFAULT_DUTY = 75
DEFAULT_RPM_A6 = 3000
DEFAULT_RPM_A12 = 2000

# Sensors
DHT_PIN_16 = 16
DHT_PIN_20 = 20
DHT_DEVICES = {
    DHT_PIN_20: adafruit_dht.DHT22(board.D20),
    DHT_PIN_16: adafruit_dht.DHT22(board.D16)
}

# Flask stuff
app = Flask(__name__)

# Global vars
fans = None
current_pwm_duty = None
current_pwm_frequency = None


def _init_pwm():
    """Inits PWM fans controls"""
    GPIO.setmode(GPIO.BCM)
    GPIO.setwarnings(False)
    GPIO.setup(FANS_PIN, GPIO.OUT, initial=GPIO.LOW)
    
    global fans
    fans = GPIO.PWM(FANS_PIN, PWM_DEFAULT_FREQ)
    

def _stop_fans():
    """Stops fans without loosing controls"""
    global fans, current_pwm_duty
    if fans:
        fans.stop()
        current_pwm_duty = 0


def _stop_pwm_fans_control():
    """Stops fans and does cleanup"""
    global fans
    _stop_fans()
    GPIO.cleanup()
    fans = None


def _set_fans_pwm_duty_cycle(percent):
    """Sets fans' duty cycle"""
    global fans, current_pwm_duty
    if fans:
        fans.ChangeDutyCycle(percent)
        current_pwm_duty = percent


def _set_fans_pwm_frequency(freq):
    """Sets fans' frequency"""
    global fans, current_pwm_frequency
    if fans:
        fans.ChangeFrequency(freq)
        current_pwm_frequency = freq


def _get_current_rpm():
    """Returns RPM values based on PWM status and its values of duty and frequency"""
    global fans, current_pwm_duty
    if not fans:
        return DEFAULT_RPM_A6, DEFAULT_RPM_A12
    elif fans and current_pwm_duty == 0:
        return 0, 0
    elif fans and current_pwm_duty == 100:
        return DEFAULT_RPM_A6, DEFAULT_RPM_A12
    else:
        return (current_pwm_duty*DEFAULT_RPM_A6)/100, (current_pwm_duty*DEFAULT_RPM_A12)/100


def _get_sensor_temperature(pin):
    """Gets tempreature mesure of a given sensor"""
    try:
        d = DHT_DEVICES.get(pin, None)
        if d:
            return d.temperature
    except Exception:
        return -100


def _get_average_temperature():
    """Gets average temperature from two available sensors"""
    t1 = _get_sensor_temperature(DHT_PIN_16)
    t2 = _get_sensor_temperature(DHT_PIN_20)
    if t1 and t2:
        return (t1 + t2)/2


@app.route("/get-sensor-temperature/<int:pin>")
def get_sensor_temp(pin):
    return str(_get_sensor_temperature(pin))


@app.route("/get-average-temperature")
def get_avg_temp():
    return str(_get_average_temperature())


@app.route("/pwm/start")
def pwm_start():
    msg = "No action taken"
    
    try:
        global fans, current_pwm_duty, current_pwm_frequency
        
        _init_pwm()
        fans.start(PWM_DEFAULT_DUTY)
        current_pwm_duty = PWM_DEFAULT_DUTY
        current_pwm_frequency = PWM_DEFAULT_FREQ
        return "Started."
    except RuntimeError:
        return msg

    return msg

@app.route("/pwm/set-duty/<int:percent>")
def pwm_set_duty(percent):
    global fans
    if fans:
        _set_fans_pwm_duty_cycle(percent)
        return "Duty is set to: %s" % percent

    return "No action taken."


@app.route("/pwm/set-frequency/<int:freq>")
def pwm_set_frequency(freq):
    global fans
    if fans:
        _set_fans_pwm_frequency(freq)
        return "Frequency is set to: %s" % freq

    return "No action taken."


@app.route("/pwm/stop")
def pwm_stop():
    global fans
    if fans:
        _stop_fans()
        return "Stopped."

    return "No action taken."


@app.route("/pwm/cleanup")
def pwm_cleanup():
    global fans
    if fans:
        _stop_pwm_fans_control()
        return "Contols stopped."

    return "No action taken."


@app.route("/stats")
def stats():
    global fans, current_pwm_duty, current_pwm_frequency
    rpm_a6, rpm_a12 = _get_current_rpm()
    stats = {
        "pwm_enabled": True if fans else False,
        "t1_temperature": _get_sensor_temperature(DHT_PIN_16),
        "t2_temperature":_get_sensor_temperature(DHT_PIN_20),
        "pwm_duty_cycle": current_pwm_duty if fans else 0,
        "pwm_frequency": current_pwm_frequency if fans else 0,
        "rpm_a6": rpm_a6,
        "rpm_a12": rpm_a12,
    }
    
    return json.dumps(stats, indent=4)


atexit.register(_stop_pwm_fans_control)


if __name__ == "__main__":
    app.run(host='0.0.0.0')