Circuit for counting ignition pulses with inductive pickup using LM2907

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Joined Oct 12, 2023
This is the circuit I used for a tacho on a diesel engine in a boat. The hall device was triggered by a magnet stuck on the crank pulley. You don't need fancy circuits on the 12v supply line, as ive used this basic circuit in vehicles aswell. The last picture is using a coil to trigger the hall for calibration purposes & 50Hz, which gives 3000rpm in this application.View attachment 74065 View attachment 74066 View attachment 74067
i need your help in one same project

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Joined Jan 23, 2018
To count ignition pulses to read RPM an LM2917 is not the best choice because it is a ANALOG TACHOMETER device. It will drive a meter very well as a great analog tachometer.
forty years ago I designed a digital input circuit for a counter as part of some development tools package. That input from a clamp on pickup used a series 1K resistor followed by a standard 2-diode clamper pair to feed a 7414 hex schmit trigger to square the signal. The challenge was setting the time base frequency so that the measuring time would provide a direct RPM count.


Joined Jan 23, 2018
Thank you so much eetechoo.

Can you please explain the LM317L circuit. what is its function????? Why is it there??
I was wondering also because the LM2917 includes an internal zener diode regulator. So it must have some resistance in the voltage supply line. The LM317Lis a voltage regulator which will be needed for the digital counter portion of the system.


Joined Sep 21, 2010
Simple & efective set up I used on a Yanmar diesel on my boat. Salvaged VDO tacho which didnot suit so only using its meter. Hall sensor sensing small magnet on crank pulley. Worked great.Tacho 4.JPGTacho 5.JPGTacho 3.JPG