About This Project
This project will read temperature and humidity from a DHT11 or DHT22 sensor and send the values to Cayenne using MQTT. The python MQTT client and Adafruit DHT sensor library will need to be installed for this script to run. Install the software prerequisites using the commands below:
sudo pip install paho-mqtt
sudo apt-get install build-essential python-dev python-openssl
git clone https://github.com/adafruit/Adafruit_Python_DHT.git
sudo python setup.py install
Wire the DHT11 as the picture below. The resistor is a 4.7k. The GPIO pin you connect to does not matter. In the example code below I used GPIO pin 17.
Wire the DHT22 as in the picture below. Again, the resistor is a 4.7k and the GPIO pin does not matter. In the example code below I used GPIO pin 18.
import paho.mqtt.client as mqtt import time import sys import Adafruit_DHT time.sleep(30) #Sleep to allow wireless to connect before starting MQTT username = "MQTT Username From Dashboard" password = "MQTT Passsword From Dashboard" clientid = "MQTT Client ID From Dashboard" mqttc = mqtt.Client(client_id=clientid) mqttc.username_pw_set(username, password=password) mqttc.connect("mqtt.mydevices.com", port=1883, keepalive=60) mqttc.loop_start() topic_dht11_temp = "v1/" + username + "/things/" + clientid + "/data/1" topic_dht11_humidity = "v1/" + username + "/things/" + clientid + "/data/2" topic_dht22_temp = "v1/" + username + "/things/" + clientid + "/data/3" topic_dht22_humidity = "v1/" + username + "/things/" + clientid + "/data/4" while True: try: humidity11, temp11 = Adafruit_DHT.read_retry(11, 17) #11 is the sensor type, 17 is the GPIO pin number (not physical pin number) humidity22, temp22 = Adafruit_DHT.read_retry(22, 18) #22 is the sensor type, 18 is the GPIO pin number (not physical pin number) if temp11 is not None: temp11 = "temp,c=" + str(temp11) mqttc.publish(topic_dht11_temp, payload=temp11, retain=True) if humidity11 is not None: humidity11 = "rel_hum,p=" + str(humidity11) mqttc.publish(topic_dht11_humidity, payload=humidity11, retain=True) if temp22 is not None: temp22 = "temp,c=" + str(temp22) mqttc.publish(topic_dht22_temp, payload=temp22, retain=True) if humidity22 is not None: humidity22 = "rel_hum,p=" + str(humidity22) mqttc.publish(topic_dht22_humidity, payload=humidity22, retain=True) time.sleep(5) except (EOFError, SystemExit, KeyboardInterrupt): mqttc.disconnect() sys.exit()
Save this file to /home/pi/python/tempsensor.py (path does not matter, just be sure to update path to match yours throughout the next steps) and fill in your username, password, and client id (lines 8, 9, 10). You can also delete the DHT11 or DHT22 lines based on which sensor you are using or add additional lines to check more than 1 sensor. The topic_dht lines will all need unique channels, so be sure the last digit in the string is unique "v1/username/things/clientid/data/ 1 "
For testing just run the file with
python /home/pi/python/tempsensor.py After it is working correctly add the widget to the dashboard permanently by clicking the + in the upper right hand. Add the python file to your crontab with
sudo crontab -e then type in
@reboot python /home/pi/python/tempsensor.py & and save. Reboot and you should see the values populate on your MQTT dashboard. To remove the script use the command
sudo crontab -e again and either put a # in front of the @reboot line you added, or delete it entirely.