Have been working on the input and output connections of the digital cockpit for the classic Honda MT mopeds. Isolating everything properly using optocouplers and MOSFETS takes quite some real estate. Now I understand why the control units for cars are so packed.
The good thing is that I can replace each set of four PC817 optocouplers with a 4-channel TLP291-4 optocoupler, and the pull-up resistors with resistor networks.
Turns out that some of the lights -- old-school filament light bulbs -- are fed directly from a separate spool circuit on the stator, which means that alternating current (AC) is used there. So in order to light up the right indicator lights in the cockpit, each raw input from these lights will have to have its own rectifier block, TVS clamping diode and smoothing capacitor before it can be fed into the optocoupler.
Fortunately, there are only three of these signals, e.g. tail/sidelight, low beam and high beam.
Alternatively, I could avoid this issue by connecting the power feed for the switches on the steer to the rectified power feed instead of the raw AC feed from the spool, but I cannot trust others that may be installing this digital cockpit to do the same. So better make sure that this input circuit works for both AC and DC.
Offerman Industries