The mini-quad challenge gate uses a laser diode and a light dependant resistor controlled by an Arduino to detect mini-quads flying through. When a mini-quad is detected it sounds a buzzer and lights up another light in the Neopixel array. See how many times you can fly through without crashing! https://www.youtube.com/watch?v=YgrbVC4IgLEYou'll need to print You'll also need Assemble the parts, line up the laser, mirrors and LDR so that the beam bounces up and down and hits the LDR then glue in place. Wire up the LDR with a resistor to make a voltage divider and connect to one of the analog pins on the Arduino, connect the Laser Diode to 5V (check it has a built in resistor) , connect the buzzer up to a digital pin on the Arduino. The attached sketch demonstrates how to read the LDR and run actions on detection.