TAPR Open Hardware License
HECA 2 is more compact version of HECA with different enclosure.
In this design we used precise temperature and humidity sensor from Swiss company Sensirion: SHT30 (or SHT31/SHT35) connected via I²C. This sensor is equipped with programmable ALERT output. This output is connected to N-channel MOSFET and controls 5W heating resistor. Huge advantage of this design is ALERT logic which can be programmed via I²C and it's independent from main micro controller. In other words apart of sensor initialization it doesn't require any action from main micro controller.
You may use HECA 2 as inline relative humidity conditioning device for other PM sensors or projects.