Digital Tach

[Stephen Burgess]

A bar graph tach made of LED's would likely be the simplest solution. The problems with a simple
electronic digital tacho's is electrical noise causing a false tack reading, analog tach's are
somewhat immune to this problem because they require a certain amount of electrical power to
overcome impedence in the coil, and they have a small amount of inertia in the needle mechanism
that helps keep the needle from wiggling with the electrical noise.

The easiest way to reduce tack input noise is to use an unductive pick-up on one of the plug
wires for your tach signal. Each time the plug fires you know that the engine has turned one
revolution. Then all you need is a counter,  a crystal, a multiplexer, and a bunch of led's.

The one trouble I ran into with this idea was that I would have a blinking LED at the end of the
bar. What I mean is that if each LED was to indicate 1000 rpm, and the engine was running at
1500 rpm, the 1000 rpm LED would remain lighted, but the 2000 rpm LED would blink. I'm pretty
sure there's an easy way to get rid of this, but my attention span was gone at that point, and I
moved on.





----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org