Tachometer Tester

[Bob Ashlock]

Here's a little product design I did a few years back for my own test-bench and recently moved forward to 'commercialize' because, according to one well-known Porsche Master Mechanic, "Every Porsche Repair Shop needs one of these.": A simple tester to determine if a tachometer is functional and reasonably accurate. Based on what I've seen with the VDO tachs, even when working, they are often surprisingly inaccurate. And I regularly run across customer situations where they can't get their tach to work because the wiring in the car is all jumbled-up.

So, here we go with a little marketing pitch about my new TACH-TEST product:

TACH-TEST is simple to use. Just connect it to any 12V source (for example, the vehicle battery) and connect the other leads (power ground and signal) to your tachometer. Very useful for checking functionality and accuracy of the tachometer as well as troubleshooting signal continuity in the vehicle wiring to the tach.

This unit works with most 4, 6 and 8-cylinder tachs. The rotary switch selects zero, 500 rpm, and 1000 - 10000 rpm steps with an accuracy of a few %. An output switch lets you choose between a low and high-level trigger signal. An LED indicates output activity.

The unit comes with a 6-foot power cord and 3-foot output leads, all with insulated alligator clips to make attachment to 12V power and the Tach quick and easy.

The output "LO" position provides a current limited 12V rectangular wave to the tach. In the "HI" position that signal is enhanced with a 150V 'spike' to trigger older points/coil-triggered tachs. These low-energy signals will not damage your tach. Unit is reverse-battery protected and short-circuit protected.

So, that's it. It will soon be appearing on my AshlockTech website.