Tachometer LM2917

Thread Starter


Joined Jul 30, 2014

I have been looking at all of the threads that deal with the LM2917 tachometer trying to find a solution. I am building an engine monitor for a rotary engine in an aircraft. I am using an arduino and want to feed the voltage from the LM2917 to the arduino. I built up a test setup that spins the CAS sensor to RPMs and measuring the rpm with a photo tach. I have tried various resistors and caps but I am getting a steady increase in voltage to about 3000 rpm then the voltage goes down. I am putting redline at 4500 rpm. Does the input voltage amplitude affect the output? Is the input voltage so high from a VR sensor that it is causing this?

I have another circuit that uses a LM1815 that cleans up the wave form and limits it to 5 volt output. It does not work when connected to the LM2017. I suspect that it is not going negative only to 0. How do I adjust the input to go negative? I am using the LM2917 circuit in the data sheet for the 14 pin chip. The LM2917 circuit uses 12 volts while the LM1815 uses 5volts. I am using a regulated supply. Appreciate any help. Thanks

Joe Berki


Joined Jul 18, 2013
Have you considered using the tach signal direct without the use of LM2917?
I am not sure of the capabilities of the Arduino, but I have done this fairly easily with a PICmicro.