Troubleshooting

This page lists common issues and quick checks when using the DE2120 2D Barcode Scanner.

Arduino

Did you scan the POR232 barcode?
The scanner ships in USB mode. You must scan the POR232 configuration barcode from the DYScan settings manual to switch it to TTL/RS232 mode before it will communicate over UART.
Check TX/RX are not swapped:
The scanner's TX must connect to the microcontroller's RX, and the scanner's RX to the microcontroller's TX. This is a very common wiring mistake.
Check power:
The DE2120 requires a stable 3.3 V supply. Supplying 5 V directly may damage the module.
Allow startup time:
Add a delay(500) before calling scanner.begin() to give the scanner time to boot.
Check wiring continuity:
Verify all connections with a multimeter if possible.

Verify Serial Monitor baud rate is 115200.
Check scan distance:
The DE2120 reads barcodes between 25 mm and 400 mm. Holding the scanner too close or too far from the barcode will result in no decode.
Ensure readBarcode() is called in loop():
The function must be polled frequently. Avoid blocking calls (delay()) that prevent it from running.
Check lighting:
The scanner works best in normal indoor light. Direct bright light or complete darkness may affect performance. Enable the white illumination LEDs with scanner.lightOn() if needed.
Check barcode print quality:
Minimum print contrast signal (PCS) is 25%. Low-quality or low-contrast barcodes may not decode reliably.
Check that the correct symbology is enabled:
If you disabled 1D or 2D symbologies, re-enable them with scanner.enableAll1D() or scanner.enableAll2D().

Increase BUFFER_LEN:
If the barcode data is longer than your buffer, the string will be truncated. Increase BUFFER_LEN (default 40) to accommodate longer barcodes.
SoftwareSerial baud rate mismatch:
SoftwareSerial may drop characters at higher baud rates on some microcontrollers. Try switching to a HardwareSerial port if available, as shown in the HardwareScan example.
Confirm baud rate after negotiation:
The library negotiates the scanner down to 9600 bps. If another sketch changed the baud rate manually, call scanner.factoryDefault() to reset to a known state.

The beep confirms the scanner decoded a barcode, but the data is not reaching your microcontroller. This usually means the UART wiring is incorrect — specifically that the scanner TX is not connected to the MCU RX.
If you previously used the scanner in USB mode, its output may still be routed to the USB interface. Scan the POR232 barcode to switch back to TTL mode.
If all else fails, call scanner.factoryDefault() to reset all settings to factory defaults, then reconnect.

Check power supply stability:
The DE2120 draws up to 190 mA during active scanning. An insufficient power supply can cause brownouts and communication failures.
Avoid scanner.changeBaudRate() unless necessary:
If the baud rate was changed and the library can no longer auto-detect it, perform a factory reset by calling scanner.factoryDefault().
Restart the scanner:
Power-cycle the breakout board and re-run scanner.begin().

Did you scan the POR232 barcode?
The scanner ships in USB mode. You must scan the POR232 configuration barcode from the DYScan settings manual to switch it to TTL/RS232 mode before it will communicate over UART.
Check TX/RX are not swapped:
The scanner's TX must connect to the MCU's RX (and vice versa). The tx and rx arguments in DE2120(tx=5, rx=4) refer to the MCU's pins, so tx=5 means GPIO5 is the MCU transmit pin → connect to scanner RX.
Check power:
The DE2120 requires a stable 3.3 V supply and can draw up to 190 mA. Make sure your power source can supply enough current.
Add a startup delay:
The scanner needs time to boot. Make sure there is at least a short delay (or a time.sleep_ms(500)) before calling scanner.begin().
Check UART peripheral ID:
Different MicroPython boards have different numbers of UART peripherals. The default uart_id=1 may not be available on your board. Try uart_id=0 or uart_id=2.

Verify the TX/RX wiring:
If begin() succeeds but no barcodes arrive, the scanner-to-MCU direction (scanner TX → MCU RX) may be disconnected or swapped.
Check scan distance:
The DE2120 reads barcodes between 25 mm and 400 mm from the scanner face. Position the target within this range.
Call readBarcode() frequently in your loop:
The function accumulates bytes as they arrive. If you sleep too long between calls (time.sleep_ms > 100 ms), you may miss the carriage return that terminates the barcode string. Keep the polling interval short (20–50 ms).
Check that the correct symbologies are enabled:
If you previously disabled 1D or 2D symbologies, re-enable them:
```
scanner.enableAll1D()
scanner.enableAll2D()
```

The internal buffer is 256 bytes — long barcodes (e.g., PDF417 with large payloads) will be truncated if they exceed this. This is a library constant (_MAX_BARCODE_LEN) that can be increased if needed.
Check for UART noise:
Long wires or breadboard connections at UART speeds can introduce errors. Keep wiring short and direct.
Verify the baud rate:
The library auto-negotiates to 9600 bps on begin(). If another sketch changed the baud rate, call scanner.factoryDefault() to reset to a known state, then reconnect.

The beep confirms the scanner successfully decoded a barcode internally, but data is not reaching your MCU. This almost always means the scanner TX → MCU RX connection is missing or broken.
If the scanner was previously in USB mode, its data output may still be routed to the USB interface. Re-scan the POR232 barcode and call scanner.begin() again.

The de2120.py file must be uploaded to the root of your MicroPython board's filesystem before importing it. Use Thonny or mpremote to copy the file to the board.
Verify the file is present by running in the REPL:
```
import os
print(os.listdir())
```

Make sure you are connected to the correct serial port and that your terminal is set to 115200 baud.
Press Ctrl+D to soft-reset the board and re-run your script.
Upload the script again if changes were not saved to the board.