You might wonder why [Kevin] wanted to build digital calipers when you can buy them for very little these days. But, then again, you are reading Hackaday, so we probably don’t need to explain it.

The motivation, in this case, was to learn to build the same mechanism the commercial ones use for use in precise positioning systems. We were especially happy to see that [Kevin’s] exploration took him to a Hackaday.io project which led to collaboration between him and [Mitko].

The theory behind the mechanism is simple but does get into some ugly-looking trigonometry. Electrically, you feed eight sine waves with different phases into the assembly and measure the phase of the signal you receive.

Pulse density modulation is sufficient for the driving signals. The math is a bit more complex, but nothing you can’t do with a modern CPU. To set the correct parameters, a PC-based test setup allowed different runs to determine the best parameters for the final implementation.

Of course, the whole thing still needs some packaging to use as either a practical pair of calipers or for unrelated positioning duty. But it does work and it should be straightforward to adapt it for any purpose.

We’ve looked inside calipers before. If you are only making measurements with calipers one way, you may be missing out.