ATtiny85 helps breathe new life into a broken scale

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Rather than toss out a broken bathroom scale, this father-son duo decided to refurbish it with an all-new electrical system.

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What do you do when your scale breaks? If you’re like most people, you either buy a new one, or don’t weigh yourself hoping that you didn’t actually gain any weight over the holidays. If, however, you are Oxford doctoral student Ilias Giechaskiel, you simply design a new electrical system for it, then build it with the help of your dad.

As the Maker puts it, “The obvious solution…was to get rid of the internal components, reuse the case and the sensors, and build everything from scratch.”

One of the more interesting techniques employed in this project is the use of a Wheatstone bridge in conjunction with a load cell to measure weight. As the voltage change in this type of setup is quite small, a separate chip was needed to amplify the signal before it was passed to an ATtiny85’s analog input. Another neat design choice was the use of the ATtiny85 with its limited input/output (IO) capability (5 IO pins plus a reset pin).

Giechaskiel explains his selection of MCU,“I like its small form-factor, and did not want to have unused pins.” However, he does admit that more I/O would have been useful to implement more functionality in the scale.

If that wasn’t enough, he programmed the ATtiny with an Arduino, as outlined in these instructions, and his new display is a nice bright red. This would seem to be an improvement over the boring gray, though if you’re not happy with the reading, it might be harder to conceal!

There are several neat concepts in this build, so be sure to check out his code, library, and schematics on GitHub. if you think you might be able to use some of these ideas!