In SX Microcontrollers, SX/B Compiler and SX-Key Tool, g_daubach wrote:

When I did the tests with one of my units, I also tried various methods of shielding w/o too much success. There are always leads going in and out. For an effective shielding, you would need a hermetically sealed metal enclosure with all in/outgoing leads passing through filters. Even the smallest opeing in the shield can act as an antenna either to transmit noise, or to receive it. Nearby sparks often produce electro-magnetic fields, like a radio transmitter. Copper or aluminum only provide an electro-static shielding but no magnetic shield, so they don't protect any lead or component on the SX board from "receiving" electro-magnetic noise. In case of sparks, these are broadband beasts of noise.

The better protection against RFI is to avoid it at the source. If there is any electric device that generates sparks when turned on or off, try to attach a filter or "snubber" to that device. Ok, in case you can't modify the source of RFI, the only way is to protect the "receiver". As Kramer mentioned, power supply leads are usually pretty long, and therefore are nice antennas. Ferrite beads around the leads (as close as possible to the supplied device) sometimes help.

You mentioned that you tried to power the SX from a battery, and nearby sparks still affect the SX. Again, the lead to the battery could act as an antenna, or any other lead connected to the SX.

As usual, discussing RFI comes close to reading a crystal ball - there are so many possible sources of trouble that often a lot of try-and-error is required.

In order to avoid that the SX goes into some unpredictable state after a spark, you might consiter activating the watchdog. This - at least - should reset the SX, giving it a "clean start".

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