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Frequency multiplier needed, anyone with a schematic?

 
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ovide_nl



Joined: 27 Aug 2010
Posts: 2

PostPosted: Wed Sep 21, 2011 3:48 pm    Post subject: Frequency multiplier needed, anyone with a schematic? Reply with quote

Hi guys

for a car project ('99 engine in a '83 car) I need the roadspeed signal multiplied by factor 5.

The signal varies from 0hz (standstill) up to about 300hz.
I realize that 0 can't be multiplied, but from about 30hz would be good to.

So the output needs to be about 150hz up to 1500hz.

Is there anyone with a good and simple solution for this?

thanks in advance!
Ivo
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Mon Sep 26, 2011 8:53 am    Post subject: Reply with quote

I think you should use a PLL solution. Build a VCO (voltage controlled oscillator) which can deliver the desired output frequency range. Apart from feeding this signal tho the engine's ECU, feed it to a divider that divides the frequency by 5 (binary counter with the outputs and reset signal suitably connected by gates). Then use a phase discriminator, for instance a 74HC4046 to compare the divided-down signal from the VCO with the signal from the car's roadspeed sensor. The output from the phase discriminator is fed via a loop filter and then used to control the VCO. Similar circuitry can be found for example in the frequency synthesizer of some two-way radios from the 70's and 80's, and the horizontal synchronization circuitry of CRT televisions and monitors is also similar.

You should check which kind of output the roadspeed sensor gives - if it is an inductive sensor delivering a sine voltage, or if it is a hall sensor delivering square impulses.
Also, the output of your circuit must be adapted to the kind of roadspeed signal the ECU wants.
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