Who doesn’t love a good surplus store? [Tyler Bletsch] just finished up this awesome clock hack by re-purposing a scrapped medical circuit board.

Ax-Man Surplus in Minneapolis has all kinds of goodies and it’s been around a long time (here’s a hack from the ’90s that source from the store). One day while digging through their inventory, [Tyler] found a bunch of scrap circuit boards with 7-segment displays. At $2 a pop, he decided to risk it to tinker with.

He quickly identified the main chip on the board to be a common LED driver (MAX7221) and began reverse engineering the board by tracing the circuit. He actually has a brilliant guide on his website about how to make circuit tracing way easier. From there it was just a matter of loading a MAX7221 library onto a ATtiny44, adding a 16MHz crystal, and since there’s an extra 2 digits available on the display… a temperature sensor too!

It’s a great little hack, and as it turned out, there wasn’t anything wrong with the boards, except for a minor typo in the company’s name. Hooray for reusing scrapped parts!