I wanted to show you guys my pup winder that I made from an old sewing machine and a calculator and provide any info that I can just because I had a hard time finding everything to make mine (I went through about 8 calculators before I got it right )
I made a plate out of plexi that the bobbin rides on and it stays on using double sided tape.
Here is the calculator. It has two wires connected across the equals key that are attached to a micro switch. If you hit "1+1" then "=" it will count up by one for each push.
The micro switch takes the place of the equals key and is positioned under the sewing machines piston so that every time it rotates, it will press the switch causing the calculator to count one revolution. In this pic you can see the micro switch which is clamped between 2 small pieces of wood and two sets of nuts and bolts. You can also see the bottom of the piston right above the switch
This calculator is from staples and is model SPL-240. Most sites/ threads just tell you find a calculator and solder to the "=" key connection points. Well these things are not marked and for the most part the locations don't make sense, at least to me. Like I said, I went through about 8 calculators trying to find the right solder points (I also had a few slips with my exacto knife while trying to free the board from the case and ended up taking out important wires.) So hopefully this will help you out so you can avoid the cost and frustration that I went through. If you get this exact calculator, lightly scratch off the protective material with an exacto knife and solder to the two wires to the connection points I circled in this pic
It should work and it will let you avoid cutting the plastic rivets holding the board in place and having to spend time searching.
And here is the first bobbin I wound on the machine with 7000 turns
My sewing machine at full speed spins about 750rpm which was a little fast for the calculator, so I just press the button down about 3/4 of the way down and cruise at a steady pace. 7000 turns took about 13mins and I stopped every once in a while to check how the bobbin was filling up. Its tough getting used to dealing with such fragile wire but hopefully I'll get the hang of it before go broke paying for the stuff.
I mostly just wanted to cover the calculator issues in the post since that was the most frustrating part for me but I would be more then happy to answer any other questions you guys might have. Thanks for looking!
-Tyler