DIY Digital Torque Wrench Made with a Microchip ATmega328

A torque wrench is an indispensable tool for mechanics, and for anyone else who works with complex machines. Some bolts need to be torqued down precisely, and just “eyeballing” them can cause failures—potentially dangerous ones. Torque wrenches tell a mechanic exactly how much torque they’re applying, and digital torque wrenches make it easier to read the current value. Redditor Vogel25 built their own digital torque wrench using an Arduino-compatible Microchip ATmega328.

If you don’t know how a torque wrench works, take a look at an analog “beam style” torque wrench (pictured below). As torque is applied to a bolt, the end of the torque wrench (above the socket) is twisted. That twist causes the beam indicator to pivot relative to the handle, and that indicates how much torque is being applied. A digital torque wrench works in a similar way, but uses sensors to detect the twist instead of the beam. The readings from the sensors are then interpreted and displayed on some sort of screen.

Vogel25 built theirs using a set of four strain gauges. Those are mounted inside of a milled slot in the heaD of a traditional wrench. The strain gauges are arranged in such a way that two are being compressed and two are being stretch when torque is applied. That makes it possible to use a Wheatstone bridge to make sense of the “floating” values. The output from the Wheatstone bridge is monitored by the Microchip ATmega328p microcontroller, and the values are shown on a small OLED display. A specific value can also be set, and a buzzer will sound when it has been reached.