I had the plan to measure the system voltage, by that the charging voltage so I can display it as well.
Currently, I am reading and learning about Aref but I am not sure how that can help with the moving supply voltage for the sensors.
The thing is that the existing gauges should, of course, still be functional. So I thought I could grab the values from the gauges and use them with the Teensy. But I didn’t think about that almost all sensor is grounded on one side. This is destroying my whole plan of course.
So if I see the oil pressure sensor for example connected to the gauge as voltage divider then I could grab the voltage supplied to the sensor and break it down with another voltage divider connected to the ground where the middle point connection should give the x - 3.3 V for the teensy.
Regarding using the measured system voltage to use as reference I meant that I could calculate the difference between current system voltage and the 12 V basic voltage of the batteries in %. In max it would be than ~17% (difference between 12 and 14,5 volt). So if the system voltage is currently 14.5 V I could subtract 17% from the measured value before I send it out to the NME2K bus.
This would not fix the problem with lost resolution but I think the resolution is still good enough without working with aref.
This all is just what I think what could work, I am not sure about this is the correct way or that it even would work!
Another thought I had was to use the teensy to power the gauges. By that, I get always shown the correct values on both, MFD and the gauges since the supply voltage is stabilized for the sensors.
This is an old Volvo Penta AQAD40B engine (1986), there are now intelligent sensors at all which correct themselves I guess.
El schema from engine attached.
Engine_EL_SCHEMA.pdf (151 KB)