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If any of 0V, 5V, ON/OFF, power or the RPi gets in contact with the Hendi Chassis the cooker and RPi will be damaged beond repair.
In the original setup a potentiometer with a built in switch is used. The switch switches the power on/off and the potentiometer controls the power. With 5V on the power pin 500W is set and with 0.8V 3500W) is set. Backside/terminals of the potentiometer:
To interface a Hendi induction cooker it's necessary to isolate the cooker (that is the chassis and all signal wires) from the RPi. For example with opto couplers. This is an example of a working schematic (tested with FOD817B opto couplers):
By adding two relays and some kind of control for them it would be easy to switch between external control and original control of the Hendi cooker
See CBP2 wiki
See https://github.com/AHm74/hendictrl
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