Having spoken to a colleague who did electronics at university, at the moment hacking the control board of my existing induction hob via the rotary encoder is our favourite attack vector. The Hendi manual is a solid “Plan B”.
While I cannot identify exactly what rotary encoder is on the control board, it looks like it has 24 stops, giving a resolution of 96 per full turn of the knob. It has 3 contacts, ground, plus and minus.
We think if I can “tap” into the plus and minus connections I can take both up to a “normally on” switch / socket combo, and then back to the controller board. This would mean that
a) when my external emulator is plugged into the socket, the rotary encoder is overriden.
b) when my external emulator is NOT plugged in, the rotary encoder is connected as normal and can be used to control power.
i.e. if my external controller / emulator goes haywire, I can just unplug and change to manual mode.
This is very close to the solution proposed at the start of this thread for the Hendi pot.
For the socket / switch combo, I think speakON connectors look good:
. This example is “normally on”. All contacts on the male and female parts are hidden, eliminating the chance of a short-circuit as is possible with microphone plugs.
I did consider a switched XLR socket, until I realised that such sockets “normally off” only, which is the complete opposite of what we require!
To “tap” into the rotary encoder, I see 2 options:
1) tap directly into the “legs” of the encoder. (unsolder, bend up, connect “out channels” to legs, “return channels” to points where legs were previously soldered.
2) cut and tap into the 1st and 2nd wire from the right on the 9 way ribbon cable, which (if I have read the pcb traces correctly) are the connection from the encoder to the motherboard.
This leaves the sticky question of how to properly isolate the external controller from the internal control pcb. It has been wisely stressed several times in this thread that this best done with optocouplers. As my rotary encoder “hack” will require 2 wires going out, and 2 wires returning, am I correct in assuming that I will need 4 optocouplers?
Thanks for your time,