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Studebaker M15A-20 "Mr. Potato Head"

Monday, January 12, 2015

Old School Sun Tach

I purchased a Sun Tach and controller off ebay and decided to upgrade the antiquated technology inside the controller. This included gutting the controller and adding a circuit board that mimics the old relay/Mercury cell design using a 555 timer IC. The timer IC is triggered by the distributor and generates a consistent voltage and pulse duration. The meter then integrates these pulses to display pulses per minute which correlates to RPM.

Here is a link to a .pdf of the design:

This design is based on this I found on the Interwebs:

And a video showing the results:


 I suspect that at the higher RPMs in the test the drill runs a bit slower because of the added load. Of course I have no way of knowing how far off the drill is since I don't have tachometer to test the speed. I have yet to install the controller and head but I don't expect any problems.