Quantity   Component name
1 × Teensy 3.1 or Arduino UNO
1 × Germanium diode Demodulates the output from the ultrasound receiver.
1 × Misc resistors and caps
1 × EasyDriver board Drives the stepper motor.
1 × HC-SR04 ultrasound range finder This commonly found unit was desoldered to provide a pair of ultrasound transducers.
1 × Pair of 3 mm diameter linear rails Taken from an optical drive (KEM-400AAA).
1 × Pair of 3 mm diameter linear bearings
1 × Limit switch Taken from an optical drive. Used as an end-of-travel switch.
1 × Stepper motor + leadscrew Taken from an optical drive. Actuates the linear motion.