Quantity   Component name
1 × Arduino Nano (clone) Purchased from Ebay in a set of 3
2 × HC-SR04 ultrasound range sensor Ebay purchase 4 years ago for a robotics project
4 × Red LEDs This came from my first Arduino development kit purchased from Oomlaut
1 × Piezo Transducer Purchased from Ebay for a tap sensor project I never did
2 × NPN bipolar junction transistor My dad recovered these from old PCBs
1 × 18k ohm resistor My dad recovered this from old equipment
1 × 2.2K ohm resistor This came from the Oomlaut Arduino development kit
1 × Hitec HS-425BB Servo Motor Bought from Cool Components for a robotics project