Re: Convert 6 cyl tacho for use with 4 cyl

["Peter D. Hipson" <mail@darkstar.mv.com>]

A six cyl puts out three pulses per revolution, the four gives two. A
divide circuit (probably best to go CMOS on this, so you don't have to
build a fancy power supply) should do the trick. The result would be
asmetric, but I suspect it would work just fine. Not exactly trivial, it
would require probably two ICs, and a few other parts, but it can be done. 

I adapted a 4 cyl tach to work on an 8 cyl diesel--piece of cake: I make a
new face with all the numbers divided by two! A CMOS opamp was used to
amplify the rpm pulses (IC, three resistors, and a couple of caps) that the
diesel sends to the ECU. Just right for this application!

At 06:06 PM 5/21/2000 +1000, you wrote:
>Two questions:
>
>1. What's the cheapest way to convert an analogue electronic tacho,
>set up for a 6 cylinder, so it reads correctly for a 4 cylinder.
>Assuming there is no access to the internal electronics, just the
>external signal from the coil. (logically, the tacho requires 3
>pulses for every two pulses the coil generates).
>
>2. What's the easiest way?

Thanks, 
        Peter Hipson (founder, NEHOG)
        1995 White NA Hummer Wagon
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