I need to know the voltage of the signal coming from the speedometer motor for the digital dash? I am sure all 3rd gen digital dash people, and 4th gen digital dash people will be interested in this! I am working on designing a cheap frequency divider for the speedo signal. That way, when you replace your rear end gears, you don't also have to change the speedo gear. And for the 4.10 people, you can actually get you speedo corrected! All you will need to do is cut the electric wire from the speedo motor, plug this thing in, and plug the speedo dash wire into the other end. Since Maxim/Dallas Semiconductor is nice enough to provide people with "Evaluation Samples" you can get the expensive part (the function generator) for free and the and/or/not logic chips are what $1.99 at radio shack each with 4 gates on them I want to make this as fast as possible though, so some things in the design could get very specific

 

lol, I kinda expected 0 responses Oh well, bump it back, and try again!

 

It supplies the ECM with a A/C sine wave output (from a spinning magnet inside the trans) which is then converted from analog to digital by a sub-processor in the ECM. The ECM then lights the appropriate LEDs on the digi-dash to indicate MPH.

Just went through this with my brother's 87 GTA with digi-dash. learned more than I ever wanted to know.

You would need to alter the sine wave to a lower frequency in correct proprtion to simulate correct MPH with steeper than stock gears. I don't think that would be easy to do but I'm not an electronic engineer.

 

Exactly, using an opamp comparing to ref voltage of ground (0), you can find when the sine wave hits 0 volts. A 555 timer running around say 400KHz into a 19 or 20 bit ripple counter, counting the pulses from the timer, from 0 to 0 on the sine wave (giving the time under a half wave in digital form) Take the counted number, (depending on the frequency I decide on) do some math, to get the frequency of the sine wave, divide by one of a few preset constants (for various gear ratios or maybe I'll design it to be an open number to divide by...we'll see), so some more math to determine the correct input voltage on the maxim max038 function generator to output the corrected frequency, and plug it's output back into the speedometer Not too hard all things considered...opamps are cheap, the function generator can be obtained for free from maxims website (eval samples) and gates are hella cheap In the end, I'm hoping the cost will be a maximum of $20. Right now though, to make sure I don't blow up an opamp I need to know the output voltage of the speedomotor. If it's over 15 volts peak, I could have a problem, but I doubt it is over 15 volts....I may just have to track down that wire now and hook it up through my multimeter.....I was hoping to avoid that though...
Right now I am waiting to hear back from an electrical engineerong board to make sure it's cool that I run the opamp with ground as the reference (compared to) voltage. Theoretically it should become an inverting amplifier if I do that, and that's not what I want...