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Clear tachometer signal

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parish99

New Member
hello, I am trying to display my engine rpm on a V8 engine using a Lm3914 dot display driver and Lm2917 frequency to voltage chip.

So far I have not been able to get a clear signal that varies positively. The bigger the voltage swing the better for accuracy, I was hoping to get about a 5v swing. So far the biggest swing I get is about 3V and it decreases instead increases, i'm not sure what values I should be using for the caps and resistors.

Has anyone built something simialar?
Any suggestions? :roll: :roll:
 

bonanz

New Member
Hi parish99,

I'm new to the board but by chance i happen to have a very similar circuit setup using those 2 chips to measure the speed (frequency) of a model scale maglev train system i am working on. the frequency input into the FTV converter comes from sensors around the track that have an adjustable output voltage, so it don't have the same problem you do, but i've been doing a lot of looking around about this configuration and just thought i might post some links to some helpful stuff i have found (most of which is for automobile tachometers).

http://www.t-r-j.com/Auto/Tach/tachometer.htm

http://www.900r.de/uk/gpz900r.html (click on tips and tricks, digital tacho)

hope that helps a bit
bonanz
 
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