Lessons Learned: Too much power, Magic Smoke!!


While working on the power supply for what will be a temperature control unit I made a grave mistake of attaching my ISPduino, formally testuino (atmega328p breakout essentially) directly to the, 7805, 5v regulator. The result was a little bit of smoke from the micro controller (MCU) and the blink led program stopped working. the burn marks in the picture were part of a failed attempt to remove the mcu.

The Setup: The temperature control will drive a peltier so I plan to drive it from a 12v 2A wall wart. That will be hooked up to the 7805, 5v regulator to run the mcu. The problem is, and I learned this the hard way, the 7805 produces 1.5A of current and the mcu only requires around 500mA.

The Fix: The solution is simple, I need to use a resistor. A 10ohm resistor will produce approximately 500mA. But note you can’t attach just any resistor. You’re generating approximately 22 watts of power. So I’ll need at resistor rated to at least 25 watts.

Good thing I made a couple backup ISPduino boards. This one is finished. If you’re interested in the files for the ISPduino board I’ll be posting them in the projects portion here shortly. Please leave comments. I hope these tutorials and lessons learned are helpful for some. Any kind of feedback is extremely encouraging.

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