AM2302 Digital Temperature and Humidity DHT22 Sensor

dht22

The DHT22 is the big brother to the DHT11 Humidity Sensor.  The DHT22 is more accurate, more stable and has a larger temperature range.

Requires 4.7k resistor

http://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging

I've had lots of issues reading the humidity which is why the code is so long. It takes a parameter HumidyPin which is the pin the sensor is attached to. I now have 2 sensors attached to the system hence why it's a parameter. It's hard coded for a type 22 sensor

The code uses the Adafruit humidity application

def pdshumidity(HumidityPin):
    if debug:
        print("Reading Humidity")
    LoopCount=0
    if debug:
        print('Trying Humidity = loop count ' + str(LoopCount))
        print("          Starting try for Humidity")
    output = subprocess.check_output(["/home/pi/pds/Adafruit_DHT", "22", str(HumidityPin)]);
    if debug:
        print("          Finished trying Hunmidity")

    matches = re.search("Hum =\s+([0-9.]+)", output)

    if debug:
        print("          Trying to find matches")

    while (not matches):
        output = subprocess.check_output(["/home/pi/pds/Adafruit_DHT", "11", str(HumidityPin)]);
        matches = re.search("Hum =\s+([0-9.]+)", output)
        LoopCount = LoopCount+1
        if debug:
            print('     Humidity loop count ' + str(LoopCount))
        if (LoopCount > 1):
            if debug:
                print('     Humidity sleeping due to failure ' + str(LoopCount))
            time.sleep(10)
        if (LoopCount > 20):
            humidity = 0
            matches = 1
    humidity = float(matches.group(1))
    if debug:
        print("          Humidity check finished")

    return humidity
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