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modifying a pulse frequency?

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Bugman53

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I need to build a curcuit to modify a pulse frequency. + or - 30-40%. This is to correct the speedometer on a motorcycle.

The out put from the sensor is +5vdc. it is a constance lenth pulse. what i need to do is slow it down by ~15%

So i have X Pusles per sec going in and i need (x-15%) comming out and i need to be able to adjust +- 30-50% would be fine.

any ideas?
 
So i have X Pusles per sec going in and i need (x-15%) comming out and i need to be able to adjust +- 30-50% would be fine.

Seems to me also that you can make a freq. doubler from an R, a C and a schmitt trigger exclusive OR gate.

There is a 4000 series CMOS programmable 24 pin DIP package frequency divider. Forgot the part number.
 
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Two methods come to mind. The first is, using a PIC or AVR, to simply measure the pulse duration, cross reference this through a calibration table to an output frequency, then output that new frequency from an output port.

The other method is to use convert the pulse duration to a DC voltage, then use this DC voltage to drive a voltage variable multivibrator. Don't have any parts in mind for this one.
 
I not quite sure i am right about the output of the sensor.

The servive manual says that it has a square wave 0 - +5vdc @ 50% duty cycle. and at 60MPH the output should be 124Hz.

The speedometer is digital. so does it work on duty cycle or count the pulses and then display the speed.

How can i test to see what the speedometer works on.

A am assuming that it counts the PPM at a fixed duty cycle.

Another forums suggested that a Binary rate multplier would do what im trying to do? that should keep the same duty cycle and modify the hz?
 
The servive manual says that it has a square wave 0 - +5vdc @ 50% duty cycle. and at 60MPH the output should be 124Hz.

A am assuming that it counts the PPM at a fixed duty cycle.

I infer from this that for every 1 mph increase the freq. increases 2 Hz and the duty cycle doesn't matter, within reason. The speedometer can then resolve 1/2 mph.
This is probably the simplest way to convert rotation into frequency. The speedometer is then a freq. meter. Going to a PW circuit seems like an extra step.

You could check it by running the sensor output into a one-shot adjusted for a pulse width of ~ 1 mS and see if the speedometer still tracks the speed up to 60 mph.
From experience, this test circuitry needs to be shielded from RFI from ignition noise or horns blowing.
 
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