Quantity   Component name
1 × SBM-20 Tube An ancient soviet Geiger Tube. Very sensitive and cheap!
1 × Radioactive Source I'll be using a small chip from an old fiestaware plate which contains small amounts of Uranium.
1 × Lead Shielding I don't want any radioation zipping around my computer!
1 × Geiger counter Kit Here I remade a small PCB with everything I needed, but you can also buy a Kit and get the pulses from the µC input.
1 × Microcontroller with USB capability Something that can measure the pulses and send a 0 or 1 to the computer, through a COM port. Here I'll be using an Arduino Leonardo clone.