pico-dht22/main.py

import network
import rp2
import time
import json
import machine
from machine import Pin
from umqtt.simple import MQTTClient
import dht
import urequests
import wifi_config
import mqtt_config

# Change this GPIO PIN where your DHT22 sensor is connected
DHT_22_GPIO_PIN = 3

# Debug Mode
DEBUG = False

def read_cpu_temp():
    """
        If you print the value of the temperature value you are going to get an integer number between 0 and 65535.
        So, we have to convert this value either to the Celsius degree scales.

        The temperature sensor works by delivering a voltage to the ADC4 pin that is proportional to the temperature.
        From the datasheet, a temperature of 27 degrees Celsius delivers a voltage of 0.706 V.
        With each additional degree the voltage reduces by 1.721 mV or 0.001721 V.
        The first step in converting the 16-bit temperature is to convert it back to volts, which is done based on the 3.3 V maximum voltage used by the Pico board.
        ref: https://how2electronics.com/read-temperature-sensor-value-from-raspberry-pi-pico/
    """
    cpu_temp_conversion_factor = 3.3 / 65535
    cpu_temp_sensor = machine.ADC(4)
    reading = cpu_temp_sensor.read_u16() * cpu_temp_conversion_factor
    temperature_c = 27 - (reading - 0.706) / 0.001721
    temperature_f = temperature_c * 9/5. + 32.0
    return temperature_f

def read_dht_22(sensor):
    """
        reads the temperature and humidity from dht.DHT22 sensor.
        returns tuple(temperature, humidity) if no errors
        returns None if there was an error
    """
    try:
        sensor.measure()
        temperature = sensor.temperature()
        humidity = sensor.humidity()
        return temperature, humidity
    except:
        time.sleep(2)
        return None

def wlan_up(wlan):
    wlan.active(True)
    wlan.connect(wifi_config.HOME_WIFI_SSID, wifi_config.HOME_WIFI_PWD)
    
    # Wait for connect or fail
    max_wait = 10
    while max_wait > 0:
        if wlan.status() < 0 or wlan.status() >= 3:
            break
        max_wait -= 1
        if DEBUG:
            print('Waiting for WiFi connection...')
        time.sleep(1)

    if max_wait == 0:
        return None
    
    ifconfig = wlan.ifconfig()
    if DEBUG:
        print(ifconfig)
    return ifconfig
    
def led_error_code(led, error_code: int):
    """Blink LED for a given error code (int). error code == number of times to blink"""
    if DEBUG:
        print("LED Error Status code: {}".format(error_code))
    
    # Run a quick 'start error code sequence'
    # So we know when LED error sequence starts
    start_sequence_counter = 0
    while start_sequence_counter < 3:
        led.value(True)
        time.sleep(0.1)
        led.value(False)
        time.sleep(0.1)
        start_sequence_counter += 1
    
    # Run real error code sequence
    blink_counter = 0
    while blink_counter < error_code:
        time.sleep(1)
        led.value(True)
        time.sleep(1)
        led.value(False)
        blink_counter += 1
    # Make sure to turn off LED when this subroutine finished
    led.value(False)
    if DEBUG:
        print("LED Error Status code finished for: {}".format(error_code))
    
    
def main():

    # Start Up Activities
    if DEBUG:
        print("Start up")
    count = 0
    led = machine.Pin('LED', machine.Pin.OUT)
    led.value(False)
    led_error_code(led, 1)

    # Set Wi-Fi Country
    rp2.country('US')
    wlan = network.WLAN(network.STA_IF)
    
    # Create MQTT Client
    mqtt_client = MQTTClient(mqtt_config.MQTT_CLIENT_ID, mqtt_config.MQTT_HOST_NAME)

    # Create DHT22
    sensor = dht.DHT22(Pin(DHT_22_GPIO_PIN))
    
    # Let's Go!
    if DEBUG:
        print("Enter main loop")

    while True:

        # Loop Clean-Up and Prep
        led.value(False)
        count += 1
        if DEBUG:
            print(f'\nStarting loop #{count}... \nWiFI Status is {wlan.status()}.')
        
        # WiFi Connection.
        if wlan.status() != 3:
            ifconfig = wlan_up(wlan)
            if ifconfig is None:
                if DEBUG:
                    print("Trouble to connecting WiFi: {}".format(e))
                led_error_code(led, 3)
                continue
            else:
                if DEBUG:
                    print("Connected to WiFi: {}".format(ifconfig))
        else:
            ifconfig = wlan.ifconfig()
            if DEBUG:
                print(f"Skipping WiFi Activation since WiFi Status is {wlan.status()} \n{ifconfig}.")

        # MQTT Conneciton.
        try:
            mqtt_client.connect()
            if DEBUG:
                print(f'MQTT Connected.')
        
        except Exception as e:
            if DEBUG:
                print("Trouble to connecting to MQTT: {}".format(e))
            led_error_code(led, 2)
            time.sleep(5)
            continue # Start back at the top of the While Loop        

        # DHT22 Reading.
        dht22_reading = read_dht_22(sensor)
        #debug_str = "None"
        if dht22_reading is not None:
            temp,hum = dht22_reading
            temp = temp * 9/5. + 32.0
            
        # CPU Reading.
        cpu_temp = read_cpu_temp()
        
        # Timestamp
        time_now = time.localtime()
        timestamp = "{}/{}/{} {}:{}:{}".format(time_now[1],time_now[2],time_now[0],time_now[3],time_now[4],time_now[5])
        
        # Build JSON Payloads
        dht_data = {
            'Location':mqtt_config.MQTT_ZONE_ID,
            'Temperature':temp,
            'Relative Humidity':hum,
        }
        dht_payload = json.dumps(dht_data)
        
        hw_data = {
            'Timestamp':timestamp,
            'CPU Temperature':cpu_temp,
            'Device':mqtt_config.MQTT_HW_ID,
            'WiFi Information':ifconfig,
        }
        hw_payload = json.dumps(hw_data)
        
        # Publish
        mqtt_client.publish("home/{}".format(mqtt_config.MQTT_ZONE_ID),dht_payload, retain=True)
        mqtt_client.publish("hw/{}".format(mqtt_config.MQTT_HW_ID),hw_payload, retain=True)

        mqtt_client.disconnect()
        if DEBUG:
            print(f'MQTT Disconnected.')

        # Sleep for a bit.
        if DEBUG:
            print(f'Finished loop #{count}.')
        time.sleep(5)

main()