Guys,

Quick question. A friend has replaced his instrument consol in his wifes car, for one that has a tacho and odometer (speedo). The tacho works fine, but the speedo uses an optical sensor (from where I don't know) that uses a slotted disk to generate the pulses, the result of which is that the speedo reads half of the true speed (ie when the speedo is showing 20mph the car is actually doing 40mph.

He has asked me if there is a way of using some form of electronics to double the count from the optical disk sensor. I did suggest replacing the disk with twice the number of slots, but he said that is impossible to do without distroying the sensor.

I was wondering if there was any way of using a small PIC to do the job. Not sure of how the current sensor is decoded (ie if its just the square wave pusles that is checked or if it already counts the low to high / high to low pusles. - If it counts just the positive going pulses, the could a PIC be used to count the change of state which would then result in twice the count and use this to base the frequency of the outputted square wave which could then be fed to the speedo receiver ?

The other issue is that if the encouder is running at 12v what would be the best way to reduce this voltage to the normal 5v level, would a simple voltage divider with two resistors work ?