Data is passed through transparently from end to end, so you can use it with any USB device at any speed. The power line has a 0.1 ohm current sense resistor an an INA169 high-side current sensor that is tracked by a little ATtiny85 chip. The microcontroller is programmed to read the current draw as well as the bus voltage and light up the strip of LEDs on the side.
The LED strip gives you a quick visual "power OK" and an indication of your power usage. But we also stream the data to a serial port so you can monitor, log and/or plot it on your computer!
The gauge comes as a mini kit with an assembled & tested PCB plus a separate USB jack and plug as shown above. The instructions on the following pages will show you how to assemble and use this handy gauge.
Please note: this is a handy gadget but it isn't a multimeter! We do some basic calibration during test, but the serial output readings are not precise and should be used as a basic guide rather than lab-grade data plots. Assume a variance of at least 0.1V and 50mA due to noise, thermal changes, etc.