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 (archive.org) Seeed Studio Music Shield v1 (archive.org) and micro-SD card with a MP3 file (shop (archive.org)) HC-SR04 ultrasonic distance sensor (eg shop (archive.org), 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.