I had an ECU for an air seeder blow up, so I'm rebuilding it from scratch using a Pi and other hardware. I got the shaft sensors reading fine, set up the relays and other switches and lights, but this one has stumped me. The markings give me nothing to go off of (Trison 91779847 Rev C gives me nothing useful), but I still have the borked board that I can trace out. The sensor is fed 12V and ground, and has a white wire that is marked for airspeed input on the wiring diagram of the ECU.

When I trace the white wire on this, it looks like it's conditioned by some diodes (two diodes, in opposite directions to ground) and a capacitor, with a pulldown resistor. The trace then goes to an opamp (TLC2272) inverted input via what looks like a voltage divider, and from there maybe feeds into the processor the board uses. Kind of hard to see from that point on.

I scoped it and if there's data there, it's in the 1-2mV range if I reference from ground, which makes the opamp make sense. But I don't have a very good scope where I am, I do have a Rigol at home that I could get.

I have built a very crude estimate of the airspeed just from the current draw of the hotwire using an ADC and shunt resistors, but I assume I can get a better reading from this sense wire if I can figure out how the hell it's working, via a reference circuit to help me understand. If you know this sensor or a similiar sensor that I can crib the circuit from, that would be awesome.