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Modified:21:41, 22 October 2013

This Rev Counter is based upon the LM2917 frequency to voltage converter IC. This is quite a versatile IC and the datasheet has some good circuit applications. The IC comes in 2 versions, 8pin (LM2917N-8) and 14pin (LM2917N) versions.

Shown right is a straight forward frequency-voltage converter using the 8 pin version giving an output of about 1 volt per 66Hz and is. The input must be AC and not a pulsed DC input.

Below is a variation off this circuit in the form of a tachometer or rev counter. It is designed for a 4 cylinder engine and the sensor is the points inside the distributor or similar pickup. The output from the LM2917 goes into an LM3914 dot/bar display driver in bar mode. The calibration of the display is obtained via VR1 and VR2. These adjust the FSD of the display. Since there is a voltage regulator in the circuit, it will run on any voltage from 7 volts to 25 although at higher voltages a heatsink may be required.

NOTE: The circuit below uses the 14 pin version.

D1 - 1N4001
D2 - 1N4148
IC1 - LM2917N
IC2 - LM3914
IC3 - 7805

Below is a PCB layout and track layout. The LED's are mounted directly to the board and should stand at least 15mm away from the surface of the board.

For better quality print out click here - (PDF)

Designed and Written by Phil Townshend 2008
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