Digital Caliper Computer Interface

Digital calipers give engineers and experimenters access to measurements in the thousandth of an inch or hundredths of a millimeter range. If, however, you’re doing scientific tests, you may have to record sample, after sample, after sample, meaning putting this tool down to do so between readings can be a chore. On the other hand, as seen in Max Holliday’s project, many digital calipers include the capability to output this data to a computer directly, you just have to know how to interface everything together.

One solution is to simply buy an interface cable, though, as these can cost in the $170 dollar range, Holliday decided to instead hack something together. The important thing for you to consider if you’re going to try this out yourself is that the calipers must feature this capability, generally indicated by a small door on the upper-right corner of the sliding housing. Inside, there will normally be four connection points, with ground and 1.5V on the outside pins, along with data and clock signals on the inner connections.

With a few pointers found here, he found that this data is transmitted in a continuous stream in 24 bits at 1.5 volts. He therefore level-shifted the 1.5V output to 3.3V and fed into a logic analyzer to further decode this data. With this worked out, input signals are fed into an ESP32 module on a special SAM32 board for the final(?) implementation, which also contains a Microchip SAM D51 microcontroller running CircuitPython. The SAM D51 handles sending the data to a computer, which is entered nicely into Excel!