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Opto Endstop v2.1 Kit

An optical switch usually used to detect when your robot has reached the minimum or maximum position of travel.
An optical endstop AKA opto endstop is a switch made out of light. When something interrupts the light-beam, then it signals the motherboard. Useful for detecting if your robot is attempting to self-destruct. ;)

Also, there are no moving parts to wear out, so they will last pretty much forever.

Click here for full documentation and sources.