Solar-Powered Digital Calipers

If you need to measure the diameter of a hole or shaft, or perhaps check the dimensions of your latest 3D print, digital calipers are extremely useful. At the same time, the cheap calipers that many of us have tend to constantly suck power from their tiny battery source, rendering them unusable in a matter of months… or month even.

This situation wasn’t acceptable for caliper enthusiast Johan, who instead modded his calipers to use solar power. While he’s not the first person to mod inexpensive calipers for better battery efficiency, his hack is ingeniously simple, and keeps things – if not intact – at least recognizable.

Here Johan removed the little LR44 cell that normally powers the calipers, replacing it with a solar panel and fourteen 100µF 1206 SMD capacitors soldered in parallel. These combine for a measured 1.5mF (1500µF) capacitance, slightly more than expected. A 3mm red LED was also implemented as a voltage regulator, dropping voltage from the panel down from a nominal 5V, to a calipers-friendly ~1.6V.

With the tiny components used, the new power source fits where the LR44 cell (nominally 11.6mm diameter, 5.4mm thick) would normally reside. Connections to the solar cell were snaked through the terminal compartment/opening. The panel itself was attached to the back of the calipers for a noticeable, though largely unobtrusive, look. It’s a clever low-power hack, which could potentially be applied to other devices with similar requirements.