Although old-school machinists usually preferred the mechanical vernier scale on their trusty calipers, many users today purchase calipers with digital readouts. These models often come with additional functions such as differential measurements, or a “hold” function for those situations where you need to maneuver the instrument somewhere deep inside a machine. Another useful feature is a data link that allows you to log your measurements directly to a computer instead of entering all the values manually.
The VINCA branded caliper which [Liba2k] purchased has such a datalink function, which requires a USB adapter sold separately. There’s a micro-USB connector on the tool itself, but instead of implementing a USB interface, this is used to carry a proprietary serial protocol – a design decision that should be classified as a crime if you ask us. Instead of buying the official USB adapter, [Liba2k] decoded the protocol and built their own interface called VINCA Reader which can be connected either via USB or Wi-Fi.
The serial format turned out to be a simple serial bus clocked out 24 bits at a time. To adapt the 1.2 V signal level to the 3.3 V used by an ESP32, [Liba2k] designed a simple level shifter circuit with a handful of discrete components. The ESP can communicate with the computer via the Wi-Fi interface [Liba2k] wrote a spreadsheet-like program; alternatively, a standard USB cable can be connected to emulate a keyboard for use with other software.
With its additional Wi-Fi function, the VINCA Reader is actually more complete than the official USB adapter, and is likely to be cheaper as well. The serial interface seems to be common to all caliper manufacturers, although many went for a more sensible connector than micro-USB. An automated reading system is especially useful if you have to make thousands of similar measurements.