Tommy Liao Gets Low-Cost Micrometers Talking Serial with an Arduino-Compatible Adapter Build
Rather than using Clockwork Tools' official, manual serial capture dongle, Liao reverse engineered the signal to build something better.
Mechanical engineering student Tommy Liao needed a way to accurately measure very small things on a budget — so figured out a trick to get serial readings from low-cost micrometers without having to connect them to a PC's USB port through the company's relatively expensive data capture tool.
"Using some analysis + hacking of the communication protocol used in the Clockwise Tools dial indicator," Liao explains of the reverse engineering project, "we create the possibility to digitally read the micrometer with less than $50 per tool. Signal analysis using an AD2 reveals that the clock and signal lines, which can be accessed through a micro-usb interface, can be extracted from the D+ and D- lines respectively."
Clockwise Tools' dial indicators include what the company says is an RS232 serial connection for reading measurements electronically, without having to peer at the digital display. While this presents on a micro-USB connection, it's not actually USB: instead, it needs a custom converter, the Clockwise Tools DTCR-01 RS232 Data Cable, and requires a manual button press to transfer each reading.
Unhappy with this manual approach, especially given the adapter costs more than the tool to which it's being connected, Liao decided to reverse engineer the connection and build an alternative using an Arduino Nano compatible microcontroller board. "The clock is shown to vary from dial gauge to dial gauge," Liao explains, "but the signals all have the same format: once every ~40ms, we have a 'burst' of a nibble. Six nibbles are communicated in this time frame, with a time division of ~1.58ms between each of these nibbles."
By decoding these bursts with the Arduino, it's possible to replace the official cable at a much lower cost — or to use them as input into some other system, with Liao suggesting such adapted tools could find use in 3D printing and computer numeric control (CNC) systems. The readings can also be taken automatically, doing away with the manual button-push of Clockwise Tools' own solution.
The full project write-up, including wiring diagram and source code, is available on Hackaday.io.