POS Hardware Overview
POS Hardware Overview
Terminals, receipt printers, barcode scanners, cash drawers ߀” how they connect and work.
What is a POS System?
A Point-of-Sale (POS) system is a combination of hardware and software used to process sales transactions. The hardware typically includes:
- A terminal (the computer running the POS software)
- A display or touchscreen
- A receipt printer
- A barcode scanner
- A cash drawer
- A card payment terminal
POS Terminal Types
| Type | Description |
|---|---|
| Traditional desktop | A full PC or all-in-one running Windows POS software |
| Android/iOS tablet | iPad or Android tablet with a card reader attachment |
| Embedded terminal | Proprietary hardware running a locked-down Linux OS |
| Self-service kiosk | Touch screen with integrated printer and card reader |
Receipt Printers
Most modern receipt printers use thermal printing ߀” no ink required, just heat-sensitive paper.
Connection interfaces:
| Interface | Speed | Notes |
|---|---|---|
| USB | Fast | Most common for tethered setups |
| Ethernet | Fast | Allows shared printer on a network |
| Serial (RS-232) | Slow | Legacy; still found on older POS hardware |
| Bluetooth | Varies | Mobile/portable POS setups |
Key specs: paper width (58 mm or 80 mm), print speed (mm/sec), ESC/POS command compatibility.
Most receipt printers support the ESC/POS protocol ߀” a standard command set for controlling the printer (text formatting, cutting, opening cash drawer).
Barcode Scanners
| Type | Best For |
|---|---|
| 1D laser scanner | Traditional barcodes (EAN, UPC, Code 128) |
| 2D imager | QR codes, Data Matrix, PDF417 in addition to 1D |
| Presentation scanner | Hands-free scanning on a countertop |
| Wireless (Bluetooth/2.4GHz) | Mobile and queue-busting setups |
Connection modes:
- HID keyboard emulation ߀” scanner acts as a keyboard; typed barcode + Enter into any text field
- CDC/virtual COM port ߀” scanner sends data as serial; POS software reads a COM port
- RS-232 ߀” legacy direct serial connection
Cash Drawers
Cash drawers are opened by the POS software sending a pulse command, either:
- Directly via the receipt printer ߀” most common; the drawer cable connects to the DK (Drawer Kick) port on the printer. The printer sends a 12 V/24 V pulse when commanded
- Via a USB drawer controller ߀” less common; draws independently of the printer
Drawer cables use an RJ11 or RJ12 connector. The DK port on the printer looks like a phone jack.
Card Payment Terminals
Card terminals (also called PEDs ߀” PIN Entry Devices) are typically:
- Integrated: connected to and controlled by the POS software via an SDK or local API
- Semi-integrated: communicate over a local network; the POS sends the amount and receives the result
- Standalone: independent device; staff manually enter the amount
Common protocols: OPI (Open Payment Initiative), SCA (Semi-integrated Cloud API), proprietary vendor SDKs (Verifone, Ingenico, PAX).
Typical Wiring Layout
Network switch
ß”?ß”€ß”€ POS Terminal (Ethernet)
ß”?ß”€ß”€ Receipt Printer (Ethernet) ß”€ß”€ß”€ß”€ Cash Drawer (DK cable, RJ11)
ß””ß”€ß”€ Card Terminal (Ethernet)
POS Terminal (USB) ß”€ß”€ß”€ß”€ Barcode Scanner (USB HID)
Maintenance Tips
- Clean thermal printer heads with isopropyl alcohol on a cotton swab ߀” dirty heads cause faded receipts
- Check paper roll alignment ߀” off-centre rolls jam and cause skewed printing
- Test cash drawer spring ߀” worn springs fail to fully open the drawer
- Update firmware on card terminals regularly ߀” required for PCI DSS compliance
- Label all cables at both ends ߀” POS installations often have many similar-looking cables