LED Power Indicators

The green led indicates that you have power of at least 4.5v. This is the minimum effective voltage for charging or running most USB devices. If the green LED goes out, you know you should check your port, shorten the USB cable, or reduce the current draw.

The blue LEDs give you an indication of the total power draw. They will light in sequence with increasing intensity. Each fully lit LED indicates 1 Watt of power ( ~200mA at 5V nominal). 1A represents a full-scale reading with all 5 blue LEDs lit. Most USB ports are rated for 500mA. Although the indicators will max-out at 1 Amp, the gauge is safe to use with devices drawing as much as 2 Amps.

Analog Output

The A0 breakout hole next to the computer-side connector outputs the voltage across the 0.1 ohm current sense resistor. This give you an analog signal of 1 Volt per Amp of current through the gauge. This is handy if you want to measure more precise current draw using any multimeter, or connect it to a different kind of gauge that takes voltage input

Serial Output

Voltage, current and wattage data are streamed in ASCII text on the TX pin at 9600 baud. Connect an FTDI friend, USB console cable, microcontroller, XBee, whatever you want that can read 9600 baud TTL serial data for datalogging, plotting or display.

Note that the logic level for the serial data out is 5V. If you are connecting to a 3.3V logic device, use a resistor divider or level shifter to bring it down from 5V to 3.3V

Example of serial output:

V: 5.5 I: 0 mA Watts: 0.0
V: 5.2 I: 383 mA Watts: 2.0
V: 5.1 I: 717 mA Watts: 3.6
V: 5.1 I: 587 mA Watts: 3.0
V: 5.3 I: 414 mA Watts: 2.2
V: 5.3 I: 487 mA Watts: 2.6
V: 5.3 I: 297 mA Watts: 1.6
V: 5.3 I: 383 mA Watts: 2.0
V: 5.3 I: 192 mA Watts: 1.0
V: 5.4 I: 174 mA Watts: 0.9
V: 5.4 I: 169 mA Watts: 0.9
V: 5.4 I: 452 mA Watts: 2.4
V: 5.3 I: 208 mA Watts: 1.1
V: 5.4 I: 157 mA Watts: 0.8
V: 5.5 I: 157 mA Watts: 0.9
V: 5.3 I: 181 mA Watts: 1.0
V: 5.4 I: 207 mA Watts: 1.1