USB-powered AA shim

I wanted to display my Hackaday Superconference badge without continually burning through disposable batteries, or having to cycle through rechargeables every other day. A fellow conference-goer shared this LiPo holder design which just fits into the badge’s AA receptacles and provides a sturdy plane to which to strap a bigger battery. I liked the fact that this didn’t further modify the badge and everything remained usable, but it was a little bulkier than I needed for a display piece.

After thinking on it a bit, I realized I’d rather use the lanyard holes in the badge to mount it as a display, but I still wanted to power it via USB–and not through the side-mounted Pico USB port. I had a USB Micro-B Breakout Board from Adafruit and a variable voltage buck circuit that were each mounted on convenient 10mm x 20mm PCBs that could easily fit within the bounds of a AA cylinder. The voltage buck could then be set to ~3 VDC to supply the same voltage as expected from two AA batteries. (And of course I’d need to bridge the contacts on the other receptacle.)

I designed a holder for the two boards that allowed a USB micro plug to attach in the middle of the “shim” design, and made room to attach stuff with heat set inserts. (Because I splurged on a set of M2 through M6 inserts 😅)

Visualization of the AA shim design; a cylinder that has been bisected longways. there are discs remaining on the ends intended to help make contact to the AA battery receptacle and there is a protruding ledge to support the voltage buck board in an odd orientation

After a couple of false starts on the 3D printer, I ended up with a super clean print that fit the heat set inserts perfectly. This might be my favorite quick build to date!

Photo of assembled shim next to a real AA battery for comparison

Photo of assembled shim plugged into a USB micro cable

Photo of shim inserted into my badge

See also