Here’s a project that we sadly let slip through the cracks a couple of years ago. Luckily [Brian] dusted it off and added an Easter Egg to the firmware in order to include it in the Fubarino Contest. The device is a rechargeable battery capacity tester. It discharges NiMH or NiCad batteries through a load resistor at about 1 Watt. [Brian] includes a discussion in his write-up about the hardware’s inability to work with 14500 Li-Ion cells. He includes enough info for you to figure out how to make changes to the circuit if you want to enable this option.
There is a MOSFET for switching each of the three battery positions. The ATmega168 takes readings from the cells once per second. It displays status information on a Nokia 5510 cellphone screen. This is where he chose to inject the Hackaday URL. When a cell’s discharge is complete, the image above scrolls onto the screen and remains there for a short time. See for yourself after the break.