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Digital automotive tach circuit?

Discussion in 'General Electronics' started by Noozer, Oct 28, 2006.

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  1. Noozer

    Noozer Guest

    Anyone have a simple digital tachometer schematic handy?

    I want to put a 4 digit LED tach into my van. Resolution of 50rpm is fine.
    Fed by the TACH output of a six cylinder GMC on distributor coil.

    If it isn't much more difficult, I'd like to be able to drive a bar graph of
    12 to 16 LEDs as well.

    A Digital Tachometer For Your Car

    Compact design features a 4-digit LED display and a bargraph. It can also
    provide gearchange indication and drive a rev limiter.
  3. Tam/WB2TT

    Tam/WB2TT Guest

    Build a frequency counter, and pick the right gate time. I think if you make
    the gate time 1/300 of a minute, the display will show RPM/100. Make it
    1/30th of a minute (2seconds), and it will display RPM/10. There is a common

  4. default

    default Guest

    That's too obvious.

    I'd stuff a down counter with a preloaded number corresponding to some
    very high RPM then use the tach signal to gate a series of pulses from
    a crystal oscillator into the counter.

    Sort of measuring period, but displaying RPM . . .

    Requires some latching/gating to display the count while the next
    count is being acquired.

    Main advantages: capable of very high resolution and fast response,
    with low pulses per revolution. The concept works; I had it bread
    boarded and up. An analog display was more intuitive and I could
    acquire the RPM in a millisecond glance, so used analog instead.
    Digital displays make more sense in slow flying aircraft IMHO.
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