Mixing voltages, making fire

Learned a good lesson today. When working with a microcontroller board like an Arduino Uno that runs on 5 volts when it’s connected to a laptop’s USB port, don’t apply 12 volts to one of the digital I/O pins. Tends to burn out parts the Arduino and kills the laptop. Luckily it was a Macbook Pro that looks to have just shutdown and started up again when the power button was pressed. Anyone know if there’s an overvoltage circuit of some sort on the USB ports that shuts down the hardware to prevent problems? Or did I just get lucky?

This wonderful and exciting lesson was learned while working on getting an Arduino to run patterns on the fire effects system for the Crucible’s Fire Circus 2011 show. Once the snarfed Arduino was swapped out for a working board, the sequence code was able to run.

The problem stems from using a 12 volt supply to drive the relay packs and trying to tie the digital pins of the Arduino to the same control lines. The 12 volt supply is currently used to manual controls. I’d like the Arduino to be able to piggyback on the same lines to also control the relay packs. I’m hoping that changing out the 12 volt supply for a 5 volt supply will let the two live and work in peace. I’ll stop by HSC tomorrow morning and see if I can find a suitable 5 volt supply.

In the mean time, here’s the first reasonably successful sequence running:

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One thought on “Mixing voltages, making fire”

  1. Hi, I did the exact same mistake the other day and I’m also interested to know if the Macbook pro is somehow protected because it also shut down and then restart with the power button… Now it seems to be OK… 🙁

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