Motorbike Tachometer

[jordan.k93]

I have a rough idea of how it works, but apart from slicing the wires that lead to the dial to work out the answer to my specific question, how does the dial function?

I am working on a college project where I'm going to create a gear shift up indicator, where a LED will trigger on the dash board when the REVs get to a particularly high level.

The easiest way I can think of doing it would be to run something off of the wire going to the rev meter, which I assume to be one of the following:

A frequency sine wave
A Current
A Voltage

That increases as Revs increase.

Does anyone know?
Do different manufacturers use different methods?

[Kickstart]

Hi

Some work from a signal from the ignition unit, others work from the signal to a coil.

The coil works by having a constant feed through it to earth, and a spark is triggered by briefly interrupting the earth. Hence the rev counter can just count the number of times the earth is interrupted.

Note that on most 4 stroke bikes they use a wasted spark system, so there is one spark on each cylinder for each rotation of the crank (so every other one is useless, hence wasted).

All the best

Keith
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[jjdugen]

Electronic rev counters usually attach to the low tension supply to the coils (sometimes via a connection from the ECU). Therefore a frequency measurement rather than a rising voltage or pulse measurement.
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[The Shaggy D.A.]

The type of signal would depend on the bike. Most common analogue setup is a frequency to voltage converter. The signal is more likely to be a pulse than a sine wave. The tacho I'm building has a microprocessor (since it's already being used for the speedo portion of the project) and servo.
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[jordan.k93]

So the consensous is that it is a frequency output from the shaft sensor to the dash instrument?

[Kickstart]

Hi

Just use the earth wire to a coil as a trigger

All the best

Keith
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[orac]

you should be able to strip back the cable without cutting the wire, once youve done that, put a scope on there. your college should have a scope and people who be able to help interpet it. this is the only way to really know what is going on.

whic remind me i should really get around to picking up one, may come in hand for the project i am currently working on
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