Making a Counter out of a Calculator

By John Fisher

This is an idea that Andrei Brodianski wrote me about after seeing my article on my counter I built for winding transformers and pickups.

The only thing I don't like about this idea is that I didn't think of it. Ha! I was a bit miffed after doing so much work on my counter and then seeing this ultra simple but effective idea.

See my "Homemade output transformer project"

With a cheap discarded calculator and about 15 minutes of work I had a counter that could be hooked up to a reed switch for counting windings for making transformers or guitar pickups.

You simply solder 2 wires to the "=" button contacts of the calculator and hook that to whatever you would use to trigger the counter. In this case it was a reed switch and a magnet. Making sure that the display is cleared, press "0" and then "+" and then "1" and then "=". From this point on, whenever the "=" button is triggered or pressed, it will add the next number to the display. The counter will then keep going as long as you want it to, into the billions.


Here is the counter that was taken apart and the wires soldered to.


Here is a very close look at the wires soldered onto the calculator circuit board. This is the "=" button connection that is normally triggered by a button on the calculator. I carefully soldered 2 very fine wires on to the contacts and then ran them out of the calculator. You have to be careful not to fry the very fine contacts on the circuit board but just solder it enough to make it stick.


This is where the 2 wires from the calculator will go to for counting the turns of the winder.


The only limitation that I found with is idea is that you can't trigger the counter faster then about 3 triggers per second. That was how it worked at least with the calculator that I used. But for me with my little hand winder, that is still just fine as I never go faster then that anyway.


Winding a pickup! The little reed switch is glued to a piece of wood with silicon near the drill chuck and there is a small magnet glued to the drill chuck. Everytime there is a turn, the magnet closes the little reed switch making contact and triggering the counter.

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