System Overview

At the centre of the device is an Arduino Nano (ATmega328P). Three electronic modules plug into it, and everything lives inside a 3D-printed housing:

1. The card reader optically senses which card is inserted. Five 3 mm LEDs (the Lichtmodul, light module) shine through the card onto five photoresistors (the Fotomodul, photo module); the pattern of light/dark spots encodes a 5-bit card value on analog inputs A0–A4.
2. The control board (Steuermodul) is the physical hub. The Arduino sits on it, and two TIP120 Darlington channels switch the 12 V loads: a membrane pump that inflates the balloon and a solenoid valve that deflates it. The card-reader and display connectors also land here.
3. The display (Displaymodul) is a single 20 mm 7-segment digit driven by a 74HC595 shift register, plus a piezo buzzer for game sounds.
4. The enclosure holds the balloon, the display window, the card slot, and the pump/valve mounts.

Power comes from a single 12 V / 3 A supply. The 12 V rail feeds the pump and valve; the Arduino derives the 5 V logic rail; the card-reader's Fotomodul runs at 3.3 V for a stable analog reference. The exact pin assignments are on the wiring page — the authoritative source for all connections.

For how the software drives all this during play, see How It Works; for the card encoding scheme, see the Optical Code System; for the full parts list, see the Bill of Materials.