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Serial Barcode Wedge vs. USB: Which Is Right for Your Scanner?

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How to Integrate a Serial Barcode Wedge with Legacy SoftwareIntegrating a serial barcode wedge with legacy software can breathe new life into older point-of-sale (POS), inventory, and data-entry systems that lack native barcode support. A serial barcode wedge converts barcode scanner data into serial (RS-232) input, allowing software that reads from a COM port to accept scanned data as if it were typed by a keyboard or sent directly over a serial line. This article walks through the components, preparation, configuration, wiring, troubleshooting, and best practices for a successful integration.

What is a Serial Barcode Wedge?

A serial barcode wedge is a hardware or firmware component that translates barcode scanner output into RS-232 serial data. It may be a standalone device, a mode within a barcode scanner, or an adapter that converts USB/keyboard output into serial format. Legacy applications that only accept input via a serial COM port can receive barcode data through a wedge without modifying their code.

Key benefits:

  • Supports legacy software without code changes.
  • Enables quick deployment of barcode scanning capabilities.
  • Often configurable for prefixes, suffixes, data formatting, and parity settings.

Typical Use Cases

  • Old POS terminals that read only from COM ports.
  • Industrial HMIs and PLCs that accept serial input.
  • Custom databases or forms that parse serial data streams.
  • Warehouses or manufacturing lines using older equipment.

Components You’ll Need

  • Barcode scanner (with configurable output modes or RS-232 support).
  • Serial barcode wedge device or RS-232 adapter (if scanner is USB/keyboard-only).
  • Serial cable (DB9 male/female as required) and possibly a null-modem or straight-through cable depending on device wiring.
  • PC or legacy terminal with an available COM port (or USB-to-serial adapter if only USB available).
  • Terminal/serial communication software for testing (e.g., PuTTY, Tera Term) or a simple script to read COM input.
  • Documentation for the scanner’s serial settings and the legacy software’s expected input format.

Step 1 — Identify the Scanner and Legacy System Requirements

  1. Determine scanner output modes: keyboard emulation (HID), USB serial, RS-232, or Bluetooth.
  2. Confirm the legacy software’s expected input method:
    • Does it read from a specific COM port?
    • Does it expect trailing characters (Enter, Tab) after scans?
    • Does it require specific baud rate, parity, data bits, stop bits?
  3. Check whether the legacy hardware supports hardware flow control (RTS/CTS) or only software flow control (XON/XOFF).

Record these details: baud rate, parity, data bits, stop bits, handshaking method, and any prefix/suffix characters required by the application.

Step 2 — Choose the Right Wedge or Adapter

Options:

  • Native RS-232 scanner: simplest — configure scanner to RS-232 mode and wire directly.
  • USB-to-serial adapter + scanner in USB serial mode: works when scanner provides a virtual COM port driver.
  • Keyboard-to-serial wedge (hardware device): accepts keyboard-emulating scanner input and outputs RS-232.
  • Firmware wedge inside scanner: some scanners have built-in settings to output directly to serial.

Ensure the chosen device supports required baud/parity settings and can add/modify prefixes/suffixes if needed.

Step 3 — Wiring and Physical Setup

  • Use the correct cable type: straight-through for DTE-to-DCE pairs, null-modem for DTE-to-DTE.
  • Confirm pinouts: typical RS-232 uses TX (pin 2), RX (pin 3), and GND (pin 5) on a DB9 connector—verify device documentation.
  • If using flow control, wire RTS/CTS (pins 7 and 8) or DTR/DSR as required.
  • For USB-to-serial adapters, install drivers on the host system and note the assigned COM port.

Tip: If unsure, start with TX-RX crossed (TX to RX) and a common ground; add handshaking only if communication fails.

Step 4 — Configure Serial Parameters

Set the wedge/scanner to match the legacy software’s serial settings:

  • Baud rate (e.g., 9600, 19200, 115200)
  • Data bits (usually 7 or 8)
  • Parity (None, Even, Odd)
  • Stop bits (1 or 2)
  • Flow control (None, XON/XOFF, RTS/CTS)

Also configure prefix/suffix characters on the scanner or wedge. Most legacy programs expect an Enter (CR or CR+LF) after each scanned code — configure the scanner to append that.

Step 5 — Testing and Verification

  1. Connect hardware and open a terminal program (PuTTY, Tera Term) to the COM port with configured parameters.
  2. Scan a known barcode and observe the received characters. Confirm the full barcode and any suffixes/prefixes arrive as expected.
  3. If characters are garbled: check baud rate, parity, and wiring.
  4. If nothing appears: verify COM port assignment, cable pinout, and that the scanner/wedge is powered on.
  5. Test with the legacy software: scan into the field where input is expected. If the application doesn’t react, confirm it listens on the correct COM port and expects the suffix (Enter) you configured.

Troubleshooting Common Issues

  • Garbled text: baud/parity mismatch. Re-check both ends.
  • No data: wrong COM port, wrong cable (use null-modem vs straight-through), or missing power to the wedge.
  • Duplicate characters or missed characters: flow control mismatch; try disabling hardware flow control or enabling XON/XOFF.
  • Extra characters: scanner configured to send prefixes/suffixes you don’t want — reconfigure.
  • Scan works in terminal but not in app: app may lock the COM port exclusively or expect different terminator. Confirm settings and whether the app requires a login/active input focus.

Example Configurations

  • Typical POS: 9600 baud, 8 data bits, no parity, 1 stop bit (9600, 8, N, 1), no flow control, suffix: CR.
  • Industrial HMI: 19200, 7, Even, 1, RTS/CTS enabled, suffix: CR+LF.

Best Practices

  • Document settings for each scanner/wedge and the legacy application.
  • Label physical cables and COM ports.
  • Use powered serial adapters or active wedges if long cable runs cause signal degradation.
  • If multiple scanners share one COM port, use a hardware multiplexer or ensure the legacy app supports multi-drop serial input.
  • Maintain firmware and driver backups for scanners and USB-serial adapters.

Security and Reliability Considerations

  • Serial links are local and not network-exposed, reducing remote attack surface.
  • Use robust cable shielding in industrial environments to avoid electromagnetic interference.
  • Plan for failover: if scanning is critical, maintain a fallback manual entry procedure or spare scanners/adapters.

When to Replace vs. Integrate

Integrate when:

  • Budget or time constraints prevent software changes.
  • The legacy system is stable and expected to remain in use short-term.

Replace when:

  • The legacy system will be retired soon and long-term support is needed.
  • Frequent interoperability or scalability needs make serial integration brittle.

Conclusion

Integrating a serial barcode wedge with legacy software is a practical way to add barcode scanning without modifying old applications. Success depends on matching serial parameters, correct wiring, and configuring prefixes/suffixes the legacy software expects. With careful testing, clear documentation, and attention to signal integrity, you can reliably bring barcode capabilities to legacy environments.

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