I started this little project with the intensions of having just a simple shift light without a lot of bulk. Something i could have just an LED or two turn on and i can put it where ever i would like. So after doing a little searching i found a few starter circuits that would get me going. Basically i started with a frequency to voltage converter, then added an op amp comparator circuit for adjustability then a transistor to power the LED. I have a few more tweeks and i need to figure out what range of frequencies i need to work in for a 4cyl motor.
Here is a short vid of how it works. On the right is a meter displaying the input frequency. I can change the ranges once i figure out what range i am in. From what i have seen i think 400Hz is 6000RPM's for a 8cyl motor. So i would think a 4cyl would be half that, but i am not sure. Once i get things working like i want them to on the bench i will set the frequencies.
