Cash Register

Overview

A cash register is the till at the point of sale: it rings up items, totals the bill, takes payment, prints a receipt, and stores the cash. This is an electronic register (ECR/POS) rather than a mechanical one, so a processor running register firmware does the arithmetic, holds the price look-up and department tables, and logs every transaction for the day's Z-report.

The cashier works against the Keyboard Assembly, a membrane key deck whose numeric, department, and function keys are read by a scanning matrix. Totals and prompts appear on the Operator Display, a touch LCD the clerk also taps to pick departments and tender, while the shopper sees the running total on the rear Customer Display. All of this is sequenced by the Main Logic Board, which pairs an application processor with an I/O microcontroller that watches the keys, the drawer, and the printer.

Two electromechanical subsystems make it a till and not just a terminal. The Thermal Receipt Printer is a direct-thermal unit that burns each receipt line onto heat-sensitive paper and cuts it off. The Cash Drawer is a steel cash box on roller slides, held shut by a keyed lock and popped open on command by a solenoid latch. Everything sits in a weighted Housing & Enclosure and runs off an internal AC-DC supply.

How it works

A sale starts at the Keyboard Assembly. Pressing a key closes a membrane contact; the key-matrix board scans rows and columns, debounces the press, and sends the keycode to the Main Logic Board. Firmware looks the item up in the PLU/department tables, adds it to the transaction, and pushes the new subtotal to both the Operator Display and the Customer Display. A barcode scanner or the card reader can feed the same transaction through the rear ports.

When the cashier tenders the sale, the controller does two things. It streams the receipt to the Thermal Receipt Printer: a stepper advances the platen one dot-line at a time while the thermal printhead pulses its heater array to mark the paper, then the auto cutter shears the receipt off. At the same moment the controller energises a relay that fires the solenoid latch in the Cash Drawer, releasing the catch so a spring kicks the till open for change. Closing the drawer re-engages the latch, and the keyed lock secures it after hours.