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# digital tachometer

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Well,

I want to set up the digital tachometer on my bike and I need a formula to calculate the frequency relation to RPM.
I tried with this one Hz=(number of cylinders * RPM/120) but..... ???
The Bike has one cylinder, four strokes and it has two sparks per revolution.

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Hi baja,

What kind of motor is this? A normal one cylinder four stroke fires once for every two revs. And this will calc. (Hz = 0.5 * revs.).

Ante ::)

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Hi Ante!

I removed the old battery ignition system and put the flywheel magneto cdi ignition.

This data I picked up from www.aet.si:
Flywheel magneto:
4-pole, rotor diameter 103mm
Triggering:
internal, 2 sparks per revolution
Spark type:
AC arc discharge
Ignition electronic:
C.D.I.

Maybe I have to calc, Hz = 2 * revs
8)

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Beats me!

Is there some gearing, say 4:1 from the crankshaft to the magneto?

Ante ::)

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Yep, I got it!! ;D

dig up the formula on the web, which is fairly simple. I have to multiply, pulses/rev*rev/min then divide by 60sec/min and that equals Hz or ignition pulses per second.
In my case; 50Hz is 1500rpm

beauty lies in simple things

Cheers!

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