Custom interface adds USB and Wi-Fi to digital calipers

Although old-school machinists generally preferred the mechanical vernier scale over their trusty calipers, many users today buy calipers with a digital readout. These models often come with additional features such as differential measurements or a "hold" function for situations where you need to maneuver the instrument somewhere deep inside a machine. Another useful feature is a data link which allows you to save your measurements directly to a computer instead of manually entering all the values.

The VINCA brand caliper purchased by [Liba2k] has such data link functionality, which requires a USB adapter sold separately. There's a micro-USB connector on the tool itself, but instead of implementing a USB interface it's used to carry a proprietary serial protocol - a design decision that should be classified as a crime if you tell us ask it. Rather than buying the official USB adapter, [Liba2k] decoded the protocol and built their own interface called VINCA Reader which can connect via USB or Wi-Fi.

The serial format turned out to be a simple serial bus that outputs 24 bits at a time. In order to adapt its 1.2V signal level to the 3.3V used by an ESP32, [Liba2k] designed a simple level-shifting circuit using a handful of discrete components. The ESP can communicate with the computer via its Wi-Fi interface, for which [Liba2k] wrote a spreadsheet-like application; alternatively, a regular USB cable can be connected to emulate a keyboard for use with any other software.

With its additional Wi-Fi functionality, the VINCA reader is actually more complete than the official USB adapter, and will probably be cheaper too. The serial interface seems to be common to all caliper manufacturers, although many have opted for a more sensitive connector than micro-USB. An automated reading system is particularly convenient if you need to perform thousands of similar measurements.