[Moris_zen] built a device to accurately measure the capacity of batteries. He needed to have an accurate measurement for the batteries he uses in a RC airplane. Knowing the discharge time allows him to fly the friendly skies while avoiding crashes from lost communications.
He based the tester around the Arduino platform. Instead of using a pre-built Arduino board he referenced the open source schematics and built the device from components to fit his needs. His solution automatically detects the battery type (Lithium-Ion, Nickel Metal Hydride, etc) based on voltage when the battery is added to the circuit. It then uses a 2.2 Ohm resistor and ADC measurements to take the battery through a discharge cycle. A character display shows status information with the ability to track discharge information using a computer to graph the data.
Apart from flashing an LED this was his first Arduino project. It’s a great use of the platform and much more automatic than other solutions we’ve covered.