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Pet Toy Beeper 2
Simple Watch Battery Holder
Pet Toy BeeperView Instructable »
LED String Lamp BaseView Instructable »
Arduino Spectrum Analyzer on a 10x10 RGB LED-Matrix
Miniature Beeping Circuit Prank
In this application the relay is needed to allow more electrical energy to power the brake lite. You can use the Digital 5 pin on the arduino as a trigger to anything. If you had an LED connected to the Digital 5 pin and ground it would light when triggered. Hope that helps. Thanks for looking!
ATtiny85 Ring Watch
RoomAlert- Intrusion Protection
Arduino Temperature Sensor Kit