Need to multiply rev counter signal ?

Hello all,

I'm after advice for a simple frequency multiplier, I need to increase the rev counter signal on my car by 1.5 i.e. if revs are 2000 I need a signal of

3000. So it needs to be 12 vdc supply 0 - 7000 rpm input 0 - 11000 output. Capable of easy build on a bit of Vero board.

Its to give the correct rev signal to a LPG system I have fitted but for some reason it only reads 2/3 of the rev's. It may be something to do with the fact that its a V6 working on a lost spark system. I.e. the plugs fire every rev not just on the compression stroke.

TIA.

George.

Thanks for the quick reply,

Its digital, and possibly a very spiky pulse. It is a wide ranging input, in that it can get its signal from the HT coil primary or a wire wrapped around one HT lead or the TDC sensor or the feed to the taco gauge.

George.

I'd say you have at least 3 alternatives to solving your problem :

1) Tougher way which though directly answers your question: Transform a typical Class C single BJT/MOSFET amplifier circuit with a parallel LC circuit at the collector/source. Choose the L and C components such that LC tank resonates at 1.5f where f is the frequency of your input signal.

2)Easier way. There is probably a microcontroller that is counting the number of revs from the engine shaft. You'll have to check for a DAC chip in your tach that changes those engine pulses to an analog voltage. They normally have an output pin where you can connect a pot to adjust the output voltages. If the pot is already there everything is simpler, so you'll avoid all the hassle of building up a seperate circuit to get the job done, which would in any case be a simple circuit. You might need the DACs datasheet to get that done.

3) Even more easier: Maybe next time....

theJackal

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I\'m confused.  If you have so many input types available it seems
like there must be at least _one_ available which would fill the

This sounds like a job for a CD4046.

You divide the frequency by 2 to feed one input of the phase detector-2 and the VCO by 3 to feed the other. Since an engine can't change RPM too fast, it would be ok, I think.

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kensmith@rahul.net   forging knowledge

Better yet, times three then divide by 2.

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kensmith@rahul.net   forging knowledge

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Don\'t you mean:

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Sounds good, will this chip need many discreet components? as you can guess electronic design is not my profession.

I'm a HVAC controls man.

George.

Go find at least a hobbiest electronics guy and suggest this to him:

----------- ! ! 4046 part 4046 part ! ----- ! ------- ----- -!D Q! ! in ---------! PD II !---/\\/\\/---+----! VCO !-------!> ! ! ------- ! ----- ! Q/!-+--+-- Out ! --- R1 R2 C1 ----- ! ! --- ! ! ! C2 ! ! GND ! ! ! ! ---------- ! --------------! Div by 3 !---------------- ----------

Both C1 and C2 will have to be film capacitors. The resistors can be done from the 4046's data sheet.

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kensmith@rahul.net   forging knowledge

Oooops yes!

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kensmith@rahul.net   forging knowledge