Quantity   Component name
1 × Raspberry Pi 2
1 × A rather hard-to-break box Be careful to choose one with a large enough opening for the Pi’s power cable as well as sufficient space so that the solenoid can be attached such that it blocks the door when it's closed.
1 × A small protoboard
6 × Resistors We used three 10 ohm resistors in parallel to obtain 3.3 ohms resistance (which we recommend to have a greater max current) and two 470 ohm resistors to obtain 235 ohms for R2 (though here a single 220 ohms would work)
1 × 1N4148 diode
1 × 2N2222 transistor
1 × Assorted protoboard wires Male-male and male-female
1 × 5V Solenoid <a target="_blank" rel="noopener noreferrer" href="https://www.sparkfun.com/products/11015">https://www.sparkfun.com/products/11015</a>