car digital tachometer 8051
Dont know of one but it should be very simple to build. Assuming u want to build one for lets say a car, here is what u do:
1. Wind a coil around the wire that connects to the spark plug. This coils will generate small current every time spark is fired in the cylinder. It is typically once in two rotations for a 4-stroke engine (so u need to double the frequency while displaying).
2. Use an Opamp like LM324 to boost the level.
3. Create a routine to measure number of spikes in fixed time. (you can do this by setting up the uC timers).
4. Do the math to extrapolate the data to per minute and display it on 7 segment display or LCD.