Ultrasonic-triggered MP3 player with Arduino

This small MP3 player is triggered when the ultrasound sensor notices someone nearby for a longer period of time (must be closer than 70cm for >0.9s). The hardware uses: Arduino Uno R3 ( Seeed Studio Music Shield v1 ( and micro-SD card with a MP3 file (shop ( HC-SR04 ultrasonic distance sensor (eg shop (, they’re cheap) Breadboard, speakers, jumper wires Optional: LED, 330 Ohm resistor (to show that it’s still running) I hacked the Music Shield to include risers for some of the pins.