Gas gauge calibration unit

Thank you all for the resistance test of the gauges.

Del, I share your thoughts the thermal gauge resistance will change, but 20 ohms is a good starting point. It equates to about 167mA maximim current. The 3V for a bit under full scale helps too. We are in the ball park, 5V * 20/30 is about 3.3V. The duty cycle for that will be a PWM value near 170 out of 255. The calibration will adjust it as necessary, the resolution will be good, much better than our ability to discern needle position .

The LM317 is adjustable, with a resistor value so we can set to 5V, or whatever works. The system will be very compliant to various senders resistances, and gauges requirements.

I could step up to a slightly larger micro controller with more pins, and accommodate temperature and oil pressure calibrations too. However without changing the scales to provide ticks and values, not much would be gained. The gas gauge in my modern car has ticks that serve as good estimates, a tick gives me about 40 miles.