converting automotive tach signal from 6 cylinder to 4 cylinder

Discussion in 'The Projects Forum' started by taiden, Jun 30, 2011.

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  1. taiden

    Thread Starter New Member

    Jun 30, 2011
    Hey all,

    Consider me a 'partially informed' newbie.

    Here's what I'm trying to do...

    I'm swapping out a 4 cylinder engine for a 6 cylinder engine in my car. If I do this, my tachometer will read 3/2 too high. I need to create a 12VDC powered circuit that will multiply an input square wave frequency by 2/3 and then output the modified frequency.

    In other words: If it sees a 600 hz frequency, it must output a 400 hz frequecy.

    As far as I know, it's a 0-12v square wave. Although, I do not have a scope to test this. It just seems to be the most common style of signal. I am unsure what the dwell is or duty or any of that for these signals, however. But I assume that tinkering will yield a usable result.

    So, can anyone help me get started? I just have no idea what to look for. Just a kick in the right direction will be nice. I'll be posting in here what I learn and my progress as well.

    The simpler it is, the better. This isn't intended to be an exercise in electronics education, although I would like to learn as much as possible. Prepackaged IC's that do 60% of the work are VERY welcome. :)

    Thanks all,
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    If it is an after market tach, like a Sun or other brand, most have a 'dip switch' or jumper wire, that is changed for the different number of cylinders. Just take the case off of the tach and it will show a wire diagram for the different connections.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    The Terms of Service do not permit us to discuss this topic -
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