RC Snubber

Switching off inductive loads causes electrical interference that can stop a nearby microcontroller.

Relays that are switching any kind of inductive load must have snubbers fitted across the relay contacts to reduce electrical interference. Inductive loads are motors, coils, relays, etc.

This RC snubber is recommended to use with the Devantech relay modules.

More information is available on Wikipedia and on the website of Devantech.