Since the time I got up and running building my own joule thief devices, I’ve been having fun lighting up LED with batteries that have otherwise been given up for dead. Most of them were AA and a few AAA, but I also had a few button cell batteries sitting around that might be good for a bit of LED fun.
Since these tiny little batteries are already weak, I did not expect very long run time out of them. And these cells on hand were in several different form factors. Given these two factors, it didn’t make sense to 3D print a battery case as I had done with with the AA batteries – the effort wouldn’t be worth the result. I just needed something to hold the contacts against the terminals of these thin batteries for long enough to drain their remaining power into some LED amusement.
Initially I tried the things that were already on my desk – paperclip and binder clip – but their naturally conductive nature meant it’s hard to avoid accidentally shorting the battery. I continued thinking along these lines during household chores, and I found my answer while doing laundry: clothespins!
Since these are made of cheap injection-molded plastic, they are not conductive like paperclips and binder clips. The cheap plastic can be easily melted with a soldering iron tip to mold around parts I wanted to mount. There is a spring to hold things tight, and the jaws open up wide enough for button cell batteries.
The bulk of the circuit was melted onto one jaw, and a wire is melted onto the other jaw. I had originally intended to run the wire through the middle of the spring, and started contemplating the best way to do so while minimizing the amount of stress metal fatigue would place on the wire.
Then I smacked myself on the forehead for overlooking the obvious: the spring is itself conductive! I don’t need to worry about metal fatigue of the wire if I recruit the spring into my circuit. So that was the final step – the wires of each jaw run to the spring, and the spring itself completes the circuit.