Control Board¶

The control board (Steuermodul, control module) is the hub of the device. The Arduino Nano sits on it, the 12 V power comes in here, and the other two modules — the card reader and the display — plug into it. It also carries the power electronics that switch the two 12 V loads: the inflate pump and the deflate valve.

Steuermodul PCB, top side — Steuermodul PCB — top (Arduino and connectors)

Steuermodul PCB, bottom side — Steuermodul PCB — bottom

Board markings¶

Marking	What it is
`Motor`	The 3-pin footprint for the pump channel's TIP120 (Motor = the inflate pump).
`Ablassmotor`	The same for the valve channel (Ablassmotor = release motor, the deflate solenoid).
`D1`, `D2`	The 1N4004 flyback diodes, one per channel, cathode toward +12 V.
`R1`, `R2`	The 2.2 kΩ base resistors, one per channel, between the MCU pin and the transistor base.
`MA`, `MM`	The pump output terminals, 12 V switched by `D6`.
`VA`, `VM`	The valve output terminals, 12 V switched by `D7`.
`Vcc 12V`	The 2-pin 12 V supply input.
`Fotomodul`	The 7-pin header to the card reader.
`Displaymodul`	The 6-pin header to the display.
`1`	Pin-1 marker, printed next to each keyed header.

The single unlabelled pads in rows beside the Arduino footprint are direct break-outs of its pins, there so a signal can be tapped or jumpered by hand.

Fitting the Nano in the Micro footprint¶

The footprint has 17 holes per row — the Micro's pin count. The Nano has 15 per row, but the two layouts are compatible by design: the Micro's pinout is the Nano's plus two extra pins per row at the far-from-USB end (its SPI pins D14–D17), and its NC positions sit where the Nano has A6/A7. Compare the two boards (both shown from the top, USB up):

Arduino Micro pinout — Arduino Micro — its extra SPI pins (D14–D17) sit at the far-from-USB end; the two NC holes fall where the Nano instead has A6/A7

Arduino Nano pinout — Arduino Nano — all 30 pins land in the footprint, aligned to the USB end (A6/A7 fall in the Micro's NC holes)

To place the Nano on the board:

USB connector toward the Displaymodul/Fotomodul headers — the same direction the Micro's USB would face. The D12 and D13 holes are in that corner of the footprint.
Align flush with that USB end. Every Nano pin then sits in the hole carrying its own name: TX1→TX1 … D12→D12 on one row, VIN→VIN … D13→D13 on the other.

Parts & datasheets¶

The components populated on the board, with the datasheet for each part archived in the repo where available.

Component	Qty	Part / supplier	Datasheet
Arduino Nano (ATmega328P)	1	Keywish Nano (footprint drawn for an Arduino Micro)	—
TIP120 Darlington transistor	2	STM (Reichelt)	PDF
1N4004 flyback diode	2	Fairchild	PDF
2.2 kΩ resistor (metal film)	2	Reichelt METALL 2,20K, transistor base	PDF

The board is also the wiring hub for the power-entry parts and the two 12 V loads it switches. These are not on the PCB — they mount in the enclosure and land on the screw terminals — but are listed here since they are electrically part of this module:

Component	Qty	Part / supplier	Datasheet
DC socket (switched)	1	BKL 072342	PDF
Toggle switch (on/off)	1	MS-165 series	PDF
Membrane pump (inflate)	1	AIRPO D2028B (12 V)	PDF
Solenoid valve (deflate)	1	CEME 5000EN1,5P	PDF

Gallery¶

Photos of the board, before and after assembly. Click any of them for a larger view.

Control-board parts before assembly: the bare Steuermodul PCB, the Arduino Nano, two TIP120 transistors, the flyback diodes and base resistors, the pin headers, and the wiring.

The assembled control board: the Arduino Nano in its footprint, the two TIP120 channels, and the Motor/valve, 12 V, Fotomodul and Displaymodul headers.

12V Power switching¶

The Arduino cannot drive the 12 V pump or valve directly, so each load has a TIP120 Darlington transistor acting as a low-side switch. There are two identical channels:

Pump channel — output terminals MA/MM (Motor), drives the AIRPO D2028B membrane pump (inflate). Controlled by MCU pin D6.
Valve channel — output terminals VA/VM (Ventil, valve), drives the CEME 5000EN1,5P solenoid valve (deflate). Controlled by MCU pin D7.

Each channel is the textbook TIP120 low-side driver: the MCU pin drives the base through a 2.2 kΩ resistor, the load sits between +12 V and the collector, the emitter goes to ground, and a flyback diode bridges the load (cathode to +12 V) to clamp the inductive kick when the transistor switches off. One channel looks like this (Dx is D6 for the pump, D7 for the valve):

TIP120 low-side switch schematic: Arduino pin through a 2.2 kΩ base resistor into the TIP120 base, the load between +12 V and the collector, a 1N4004 flyback diode across the load with its cathode toward +12 V, and the emitter to ground. — One channel of the low-side switch — the pump and valve channels are identical, on D6/MA·MM and D7/VA·VM respectively

The design basis is the TIP120 tutorial, archived here as Motorsteuerung.pdf.

Connectors¶

Everything meets on this board:

Connector	To module	Pins
Fotomodul header	Card reader	7-pin (3.3 V, `A0`–`A4`)
Displaymodul header	Display	6-pin (5 V, `DS`/`STCP`/`SHCP`/buzzer)
Power input	12 V / 3 A supply	via switched DC socket
Pump output (MA/MM)	AIRPO pump	12 V, switched by D6
Valve output (VA/VM)	CEME valve	12 V, switched by D7

Fritzing source: Steuermodul.fzz.

For the complete, authoritative signal map — including which analog and digital pins each connector carries — see the wiring.