Monday, April 8, 2013

AVR Atmega dehumidifier controller board

You can find an update for this project here:

Suddently my dehumidifier stop working, the original humidity switch get broken, it was a mechanical hygrometer, based on a thin transparent strip that react to humidity and engage the main electronic switch. So i decided to build my own dehumidifier board.

AVR dehumidifier is an alternative electronic board for your dehumidifier based upon AVR Atmega8 micro.
When ambient humidity reach the humidify threshold set by the user dehumidifier starts.
A full sensor check the water tank, if it is full the dehumidifier stop running.
An antifrost temperature sensor can shut the compressor down to prevent evaporator frost.
An ambient temperature sensor prevent the dehumidifier to run if temperature is too low or high.

  • set the humidity threshold between >30% to 80% RH< *
  • when ambient humidity reach humidity threshold dehumidifier start running it stop running if ambient humidity goes below humidity threshold minus a constant humidity off range >2% RH< *
Water full sensor:
  • check the water tank status - if the water tank is full dehumidifier stop running
Ambient temperature sensor:
  • check the ambient temperature - the dehumifier only works if ambient temperature is between >5 and 35 celsius degree< *
Humidify temperature sensor:
  • check the ambient humidity
Evaporator temperature sensor:
  • check the evaporator temperature - if it is below >7 celsius degree< * the compressor is shut down until evaporator temperature reach >7+5 celsius degree< *
Power, Full, Running led status:
  • Power led
    • blink: system running
  • Full led
    • off: water tank not full
    • on: water tank full [dehumidifier stop running]
  • Running led
    • off: dehumidifier not running
    • on: dehumidifier running [fan on, compressor on]
    • blink: dehumidifier running [antifrost cycle: fan on, compressor off]
  • Full led and Running led
    • blink: dehumidifier not running [ambient temperature too low]
* setup those parameter at compile time if you want different values, also you can setup different port values if you want different board connections.

Selected humidity sensor is DHT22, but it can also work with a DHT11 sensor. Antifrost sensor is an NTC thermistor.

This library was developed on Eclipse, built with avr-gcc on Atmega8 @ 1MHz.
If you include <math.h> add libm library to linker.


  • 1.0.4: DHT library update
  • 1.0.3: first release


  • read risk disclaimer
  • excuse my bad english


  1. Thanks for the information. I've been shopping around for a dehumidifier rental and reading reviews for the past few hours trying to figure out which would be the best for a medium sized basement. I have tons of electronics and lab equipment, as well as chemicals down there that I am worried the humidity may destroy.

  2. First You got a great blog .I will be interested in more similar topics. i see you got really very useful topics , i will be always checking your blog thanks. Best dehumidifier

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