So a few months ago, I stumbled upon a thing at Adafruit.com called a "Charger Doctor" which was really just a Multimeter designed to slip inline with your USB cable. It was $7.50 and I liked it.

When working on electrical projects around the home—whether that’s troubleshooting an issue with your HVAC system, repairing an appliance, or testing a car battery—a multimeter is essential. These ...

This circuit senses AC audio voltage supplied to the car-radio loudspeakers and displays it as power using a LED bar graph, achieving at the same time an attractive visual effect. It is designed to ...