I have an old vehicle from the 70's and it has a gauge for oil pressure. I want to add a 12v LED to the dash that will light up when the oil pressure is too low.
The installed sensor on the engine is restive to ground. The resistance changes as the oil pressure changes (more pressure = less resistance), thus changing the reading on the dash gauge. I want my warning light to be connected to this same sensor.
Note, although vehicle is 12 V, it has a factory "constant voltage unit" that provides the gauges with 5 V. I will be replacing this with a simple 5 V regulator (eg LM7805). So gauge circuit will be...
+12v----LM7805----Gauge----Sensor----Ground. The circuit for the LED indicator would connect between the gauge and sensor.
In the past, I've been able to accomplish this with an Arduino and some code, but don't want to use an MCU in this application. However, I can't seem to figure out how to do this with a simple discreet component design.