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Rev Counter Problem need info on a signal divider

  1. Apr 14, 2009 #1

    i know that this is probably not the best place to look for help but i have been to alot of forums with no real result . The problem i have is that we changed the motor on my car form a 4 cyl 2l witch gave me 2 pulses per revolution to a 2.5 v6 but this motor gives 3 pulses . its form a seperate wire from the ECU . the only other info i have is that the signal does not come from the coil on the car , at idle the signal is 25 Hz and above 2500 rpm its 125Hz . to give a idea how mutch its over reading with the old motor at 120km/h in top gear it was sitting at about 3500 rpm , same speed on new motor its about 5500 rpm . the info i got was that i need to divide the signal by 1.5 and that Possibly a 4046 cmos part with x4 output and a bit of logic to divide it back down by 6 would do the job.

    The main problem is me because i never had a chance to learn about electronics , the only time i can build something is if i have a diagram :redface: .

    Thank You for your time
  2. jcsd
  3. Apr 14, 2009 #2


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    Staff: Mentor

    Welcome to the PF. It might just be simpler to change the memory chip in the ECU to the one that matches the new engine. Is that a possibility? Probably get better performance with the correct ECU chip as well.
  4. Apr 14, 2009 #3
    I think you can do it with two chips. First, you want to multiply by 2. Use the CMOS 4070 exclusive OR (XOR), and put the input signal into two inputs of the same exclusive XOR, with one signal delayed by say 100 microseconds by using an RC delay circuit. Each input pulse in will then give two pulses out, separated by 100 microseconds. Then to divide by 3, use a CMOS 4017 one-of-ten decade counter, and use the "3" output to reset the counter (you may have to invert the signal by using one of the unused XORs), the reset signal will then be a divide by 3. You may want to buffer this output with a transistor. You may also want to use a one-shot (monostable) to stretch the output pulse.
    Last edited: Apr 14, 2009
  5. Apr 14, 2009 #4


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