Monday, September 2, 2013

AVR Atmega dehumidifier controller board, update

This project is an update to the previous dehumidifier based you can here:
This update adds some usefull functions.

The main issue that i've fixed is the microcontroller crash, that happens sometimes. I've noticed that sometimes the controller stop running, crash or doesn't works as expected.
After some experimets, i've noticed that probem was due to Electromagnetic Interference (EMI), EMI happens when the compressor and fan starts or stops.
I've solved this issues by:
  • insulating relays with metal tape
  • outdistance relays from the microcontroller
If you look at the image below you can see that relays are not distant from the microcontroller.

To build a more secure controller, i've added a watchdog control to reset the microcontroller if anything goes wrong.

Another improvement to the previous design is the additions of a minimum off/on time to prevent the compressor to be switched on and off in a short time. Some compressor may get broken if those timed function does not exists.

Finally i've switched the DHT11/22 sensor with an AMT1001 sensor. The AMT1001 sensor is less sensible to EMI, and it has analogic output.

  • 1.0.9: added offset calibration for humidity/temperature sensor
  • 1.0.8: fix minimum on/off compressor time with antifrost temperature.
  • 1.0.6: DHT switched to AMT1001, add watchdog, add minimum on/off compressor time.
  • 1.0.4: DHT library update to prevent blocking.
  • 1.0.3:first release.


  • read risk disclaimer
  • excuse my bad english


  1. Hi Davide,

    In past not so far I bought a dehumidifier that does not woks anymore and I would like to try make your solution what I thought great. First I would like to know if it has any problem to use it only for my personal problem, If it is OK, I would like have some help where I should put the evaporator temperature sensor, the humidity sensor is clear on pictures.

    Since now I thank you very much for any answer.


    1. you can see the antifrost NTC on the right, next to the dehumidifier grid in the picture here:

      the main temperature and humidity sensor is the blue one here

      in my house, attached to my humidifier it works with no problem.


    2. Hi Davide,

      Its me again. I updated to firmware 1.08 version, and looks like is working, but the compressor heats up after a time and aparently it daoes not works regurlarly. I think maybe the temperature, and humidity may not bereading acordenly. How you use the tx to debug once the level is TTL and not RS232 levels? Did you made an interface circuit, or used a special terminal, or what?

      Thank you in advance.

    3. You can use a cheap USB to TTL board, like the CP2102.

    4. Thank you very much. Helped a lot.


    5. You are welcome ;)
      Happy to hear this!

    6. hello.Davide

      for this Atmega dehumidifier the pot P1 what is the value?.thancks