[over9k] used his Arduino to set up a laser trip wire. The laser is mounted along side the Arduino, reflects off of a mirror, and shines on a photoresistor that interfaces via a voltage divider.

Lasers are some of the coolest devices around. We can use them to cut things, create laser light shows, and also as a rangefinder.[Ignas] wrote in to tell us about [Berryjam’s] AMAZING write-up ...