Hi Kyle. I’m a beginner with the Raspberry Pi and came across your Mycodo program by pure change. I’m a mushroom cultivator and on recommendation decided to automate my rooms to ease my workload. The Mycodo program is brilliant and I must thank you for this great program. I’m using a Raspberry Pi 2B v1.1. Temp sensors are DHT22 x 2 that works in my fruiting and incubation rooms. All my functions are working well including my PID’s. My issue started when I wanted to add my humidifier to the 8 way relay board that is connected to my Pi. The humidifier is homemade, meaning it is a 12vdc PC fan and a 20VAC ExoTerra Fogger that I ran from a janus plug on 240VAC. The problem arise when the PID starts the humidifier, it then drops my DHT 22 sensors to zero a reading. When I look in the deamon it confirms that it doesn’t get any reading from the Influxdb. It drops the incubation sensor first most of the time and when I reset the sensor the fruiting sensor goes down. It keeps on happening until I remove the humidifier and then the sensors are stable again. Both sensors are connected to a breadboard on 5v with a resistor between the 5v and the data line. I even created two different PID’s so that the 12vdc fan and the 20VAC fogger ran on two different relays. It still keeps on dropping the sensors. Is there any suggestions you can offer as I’m little lost to what might cause the problem.
Hi Pieter,
Welcome. I’ve been in your position with the exact same problem with the DHT22. You’re likely experiencing interference introduced by the relays in your system, which is causing the DHT22 to fail. The DHT22 is very sensitive and I no longer recommend its use. There are far better sensors such as the SHT31, HTU21D-F, and BME & BMP series temperature/humidity sensors (among others) that work really well and I haven’t had issues with relays interfering with their operation.
If you wanted to continue using your DHT22s, what you can do it try to reduce interference by isolating the sensors from the relays, physically and electrically This may not be easy or possible. You could also try using a solid state relay if you’re currently using mechanical relays. Other than that, I haven’t done much experimentation with diagnosing DHT22 issues, I used it as an opportunity to move on to try other sensors.
Hope this helps
Cheers
Hi Kyle
Many Thanks for your speedy reply. I will be trying the solid state relays and hopefully it will solve the problem. Will keep you informed should it work.
Pieter
Hi Kyle
Thanks for your advise in the previous post. I have changed from mechanical relays to ssr and the problem has stopped. System is running 48 hours without any sensors going down. System very stable.
Many thanks again
Pieter
Good to hear it worked and thanks for the update.