Yeah, thought about the mcu-in-the-middle as well for the keypad. But then you'll have to keep track of the UI state, which can get annoying real fast.
Not neccessarily: At least with the current firmware, most buttons do not have any functionality when you are in regular shooting mode. So you might either check for combinations like
Back-button (upper right button) pressed
together with up / down and left/right
or just using these buttons as they do not have any function anyway:
Some ideas:Enable manual temperature mode: pressing 'back-button' for >1 second
up/down: setting upper temperature (each short click +/- 0.5°C for example; each longer click +/- 5°C)
left/right: setting lower temperature
disable edit mode: pressing middle button
Also a remember function might be useful: entering the edit mode and then pressing the middle push button first, will set the values used last time and exits edit mode.
Well, the above will work if you are not in locked mode, but it will also do no harm.
Any other ideas which could be useful and which can be set by the UART interface?
As my camera is still closed (only removed the front yet to get access to the UART connector): does anybody know how many wires the FPC for the keyboard has? I assume 0.5mm spacing? The current functionality indicates that the E4 is not using a matrix but single lines for each button = then 9 wires would be needed as minimum.