Jeff Keyzer used five of his own MightyOhm Geiger Counter kits, an Arduino Uno R3, a Sparkfun Music Instrument Shield, and an Adafruit Protoshield to create this geiger counter musical instrument for Maker Faire.
The PULSE output of each Geiger counter is connected to one input of a 74LS04 hex inverter on the Protoshield. Each time a Geiger counter detects a radioactive decay, it sends a 0.1ms 3V high pulse to one input of the inverter. The 74LS04 functions as a level shifter and outputs an (inverted) 5V pulse that is suitable for driving an ordinary (5V) Arduino.
