Electronic – µC (Arduino) and Dealing with thermocouple noise

The reality is that you most likely did fry it. We can think about it this way: you supplied much more voltage to it than it was designed to handle, and now it doesn't respond to your computer. What other possibility is there?

The question now is: what exactly did you fry? One thing that could very well be toasted is the ATmega328 chip. Whether you are in luck or not depends largely on whether you have an UNO with the SMD chip or the DIP ATmega328. If it is the former, and the chip is dead then you'll need to get a new Uno, unless you have advanced soldering equipment. If it is the latter you can buy a new ATmega328PU and replace it in your Uno, however, even in this case the solution isn't necessarily easy.

The problem is that you'll need to get a bootloader onto your new ATmega328PU, and without an Arduino or an ISP programmer this isn't easy to do. Fortunately, ATmega328PU with bootloaders already on them are sold on ebay for just a few more dollars than the bare ATmega328PU which runs about $3-$4.

It could also be the case that other (non-MCU) components are damaged either instead of, or (worse) in addition to the MCU: the USB interface chip, voltage regulators, or any of the many passive components that are directly connected to the +5 rail. The trouble is that even with a multimeter it may be difficult to assess the damage. For my money, the best option is to buy a new Uno and move on, however, if you are interested in a (potentially complicated) project, at least the schematics are available. So you would want to look at the schematic drawing and test at least every component that is connected to +5 and ground. Then you might want to test every component connected to those components, in case the blown out component shorted out something else. In the end you might have to test everything.

The alternative strategy would be to assume the best, and look, and maybe try to smell the damage, and replace one or two components that look suspect, and then pray for the best.

The solution was to physically separate the power connections for the audio components. While @Dave mentioned in the comments something about a star ground topology, the problem was that while the ground connections were all centralized, the Vcc connections were also, and shouldn't have been.

In the original design, power was supplied to the entire assembly via a small PCB with header pins for each separate component. Two rows of male header pins, one for 12V DC and one for ground. In this arrangement, all of the noise was being dumped onto the audio components each time the servo motor was actuated. Adding capacitors helped slightly, but certainly not enough.

The main two wires supplying the small power distribution PCB are about 10 cm long. I added a second pair, and created a second power distribution PCB. The original one was used for the servos and receiver, while the new one was used for audio and amplifier. The "Y" split in the power cable ultimately had the effect of keeping the power clean on the audio side.

I also removed the ground connection between the RC receiver and Arduino, though this was unnecessary. Its presence did not add noise, nor did its absence cause triggering problems.

An electrical engineer coworker advised me that it was important to have separate power supplies for motors versus digital components. While this project still only uses one power supply, the solution was to split the power as early as practical, and dedicate each to its respective purpose.