Quantity   Component name
1 × ZX Spectrum An original Sinclair ZX Spectrum with a working keyboard.
1 × Ardunio Pro Mini A 5V ATMEGA328 based clone will work fine.
1 × 2.2KΩ Resistor
2 × 68Ω Resistors
2 × 3.6V Zener diodes Must be rated at 0.5W or less
1 × USB A plug and lead You can reuse an old USB lead
1 × Short length of cable Ribbon cable is prefect but I used old Cat5 cable