Guys, I am experimenting with a noisy signal and trying to gather a frequency of specific peaks.
Yes, it comes from my 12V car plug and I want to use it for a simple RPM meter. I do it for fun and experience, nothing else. The car is old Corolla e11 with a four stroke engine. I used my ds1074 scope to take a sample (5 MSPS, 1,2Mpts) of the AC coupled signal on 12V voltage rail in a car.
You can see the results below. It can be seen that ignition peaks are significant but simple voltage level triggering would not be sufficient. There are additional random (spurious?) peaks. The difference between the peak of my interest and the other unwanted noise is in the duration. The real ignition peak has about 50us duration. The false one is much shorter.
I think it should be enough to measure revolutions between 500 to 6000rpm so frequency corresponds to 33,3 to 400 Hz (RPM/60 * 4strokes).
I have few ideas but before I post them I would appreciate your first.
Thanks in advance