If you want a snack, Matty Benedetto of Unnecessary Inventions thinks you should have to earn it. To fight the temptation to gobble down treats without doing some work first, he built a lock box that can only be opened after the owner takes a certain number of steps. The idea is that you put your snack inside, then dial in the number of steps you need to take to burn all of the calories it contains. After all of the steps have been taken, the door pops open.
The internal hardware (📷: Matty Benedetto)
The lock box is built into a 3D-printed case with a handle that looks something like a lunchbox. UV-printed lettering and laser-cut acrylic pieces were added as finishing touches. A rotary encoder and a pair of seven-segment displays on the front allow the number of steps to be set after it is closed. A pair of powerful electromagnets keep it sealed tightly against prying fingers, and an accelerometer is used to count steps. The system appears to be controlled by an ESP32-based development board.
In a test of the finished system, Benedetto loaded a bag of gummy bears into the lock box and set the number of steps equal to the number of calories in the candy. After that, he went for a walk to get some steps in. A window on the back of the lock box showed what was contained inside for motivation — and this was necessary, because it was a lot of steps. But when the counter finally reached zero, the lock popped open. Ah, the sweet taste of success!