My BoArduino ATMEGA328 died a good death this weekend in the service of making an nifty CNC project. Two errors may have hastened its demise. First, I was using low-resistance pull-up resistors that I accidentally soldered into my first prototype board (470 ohm instead of 4.7kohm or the 10kohm I currently use). Secondly and most importantly, I had changed my BoArduino ground voltage from 0V ground to -12V ground. I was connecting my BoArduino I2C connection to the prototype stepper motor driver, but my seldom-used prototype stepper driver board power jack was still hooked up to the now-obsolete 0V ground. The result was that my BoArduino thought GND=-12V and "+5V"=-7V, while the proto-stepper driver thought GND=0V and "+5V"=+5V. The small values of the pull-up resistors probably contributed to what happened next: the I2C interface would not connect, and a few minutes later, I noticed ATMEGA328 and its surrounding components had became burning hot. After shutting down I was surprised to find the ATMEGA328 still could burn new programs from the Arduino bootloader, and could still blink, but the I2C interface (on the ADC Analog pins 4 & 5) would not connect. I switched to my Arduino, and diagnosed that the BoArduino ATMEGA328 had fried its I2C. RIP.