Opossum shared his Wattmeter project on the 43oh Forums using the TI INA219 bi-directional current and power monitor and a Nokia 5110 LCD display.
This is a simple voltage and current meter that uses the TI INA219 chip. Voltage measurement range is 0 to 26 volts with 4 mV resolution and current measurement range is -4 to +4 amps with 1 mV resolution (when using a 0.01 ohm shunt). The specs are inferior to a pair of quality multimeters, but it is a fraction of the price and shows wattage in addition to voltage and current. The Nokia 5110 display is used so the firmware could be enhanced to do simple graphing. Sending the measurements to a computer could also be done.
