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.
Connecting the temperature sensor for the (air-cooled) head on the other hand is surprisingly simple. The ring-shaped sensor is placed under the spark plug and its resistance decreases as the temperature gets higher (NTC).
The #KOSO sensor I'm using adheres to the 'JIS D 0203 S2' Japanese automotive standard, which means that a standardized table and some interpolation can be used to translate resistance to temperature. Reading the value from the sensor requires no more than a voltage divider connected to an ADC entrance of the MCU.
Offerman Industries