Hey hey. I want to read a tach signal from a vehicle with a PIC microcontroller. I need a pin to go low once the RPM's exceed a set point. It's basically the same as a remote start module that shuts off the starter once the car is running on it's own. The software isn't the problem, though; it's the signal that I need to read. It's got a big spike and then stays high and then goes low and then goes sort of high and then the big spike again and repeat. You can see the attached pics.
I would like to know what I need to do to get the signal readable by the mcu. I know I need to get rid of that big spike. I know that I need to get the voltage down. I don't know what I need to do to that sort-of-high section of the signal. I think an RC filter would be good for the spike. I would also like to keep the signal being read intact. I believe that I would use a unity-gain buffer for that.
The last criteria that the solution must meet is to work in other vehicles. The general waveforms will be the same (rectangular), but the spikes and noise will be different. I also don't know about that sort-of-high section. I have to hook up the o-scope to some other vehicles to see if that is common or not.
This is my first delve into the world of waveforms, so any help/info would be sweet.
You can see the overall waveform here.
Here it's a bit zoomed in and you can see the sort-of-high part.
And here you can see how large the spike is.
I would like to know what I need to do to get the signal readable by the mcu. I know I need to get rid of that big spike. I know that I need to get the voltage down. I don't know what I need to do to that sort-of-high section of the signal. I think an RC filter would be good for the spike. I would also like to keep the signal being read intact. I believe that I would use a unity-gain buffer for that.
The last criteria that the solution must meet is to work in other vehicles. The general waveforms will be the same (rectangular), but the spikes and noise will be different. I also don't know about that sort-of-high section. I have to hook up the o-scope to some other vehicles to see if that is common or not.
This is my first delve into the world of waveforms, so any help/info would be sweet.
You can see the overall waveform here.
Here it's a bit zoomed in and you can see the sort-of-high part.
And here you can see how large the spike is.