There are 2 channel and 4 channel controllers. Both versions are powered from 12V power supply with cigarette plug. There is 4A fuse in the plug limiting the total power available to all heaters to 48W. Each channel is limited to 36W.
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Short press switches between channels

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Long press activates power level mode

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In power level mode, short press adjusts power output. Each light represents 25% of total power.

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In power level mode, long press turns the mode off. After that short press switches between channels (see point 1)

Get the controller from the dewheater.com
Source code for the controller firmware is available from github repository
Flashing instructions are described in flashing section.