I am in the early stages of learning (everything) to use an arduino to measure engine RPM. the range i am interested in is 10hz to 50hz
This is far beyond my skill sets. So am hopefully asking for general advice that will point me in the right direction. So far I have learnt to operate a stepper motor watching Youtube.
I dont want to do an invasive method to take off a mechanical opening and closing of a switch for instance but I think my best approach would be to make an induction coil that would pick up a magnetic pulse from the spark plugs(1 or all 4) or perhaps from one of the two coils..(i am guessing this is a noisy environment)
Although the coils are switched from a 14v supply (at the above frequency) i think it dangerous (or beyond my skill set) to get a connection from there.
My thought is to make a coil and put my mini oscilloscope on it and try to work out what signal i might be able to use (oscilloscope arrives in a week).....
My problem will arise as soon as i try to use that signal on the input pins of the arduino and it crosses my mind that there must be something out there already suited to working with my dilemma......
Could I be looking at a reed switch type idea or a magnetometer on a chip? please bear in mind it has to be simple and maybe I can use math to calibrate what i get to the engine speed
Next I have to try and count the pulses in a given time frame (1-2 secs nominally) and retake samples regularly (5-10 secs nominally) and use that information to make adjustments to the stepper motor(s)..
This is a low speed application btw - not looking to make things go faster or consume more fuel etc
Thanks even for reading my hair brained idea and any advice/direction gratefully anticipated