Built rev 0.1.1 of the power meter, at this point the initial round of firmware is complete and some hardware bugs have been fixed. The buzzer seems to work, but is not yet used as an indicator. All 3 INA219 sensors are communicating though the I2C isolator, and the Xmega is performing the math to send current and voltages to the host over usb (CDC Device Class).

This marks the midway point of this project. The goal was to get build a device that could measure current and voltage, with select-able settings for high range or high precision measurements of small currents, with electrical isolation from the USB interface. This board meets the requirements, at the expense of being a bit overdesigned. A lower pin count xmega could have been used, as well as potentially a single INA219 and a rotary selector. However… I am a fan of over-design, and the prototype as built can measure 3 different loads (at different max current/precision, all must share common ground) at the same time.

I have been pretty happy with the XMega so far, I should have switched off of the megas sooner. Next project should probably involve a STMicro arm, they are a lot faster and cheaper, and seem to have comparable peripherals…

Some additions need to be made to the firmware to finish this off. There is no way to send commands to start or stop a measurement, and the 2nd I2C bus that is intended for integration with other uCs is not used. I also need to be a able to notify the device which resistor the small current INA219 is using.