Read barcodes with the trigger button

What this example shows

The scanner stays in its default manual mode: press the trigger button on the board, and the code it reads prints in the shell. The example only polls readBarcode(); the button starts each scan.

Wire the controller's pin 5 (TX) to the scanner's RX and its pin 4 (RX) to the scanner's TX, plus 3V3 and GND, or change tx and rx to match your wiring. Switch the scanner to UART first by scanning the POR232 configuration barcode.

The example code

from machine import UART
from de2120 import DE2120
import time

# Adjust tx and rx to match the pins you have wired on your board.
scanner = DE2120(tx=5, rx=4)

if not scanner.begin():
    print("DE2120 not detected. Check wiring.")
    raise SystemExit

print("DE2120 ready. Press the button on the scanner to read a barcode.")

while True:
    barcode = scanner.readBarcode()
    if barcode:
        print("Scanned:", barcode)
    time.sleep_ms(20)

🔗Open the complete example

Examples/de2120-readBarcode.py at commit 848e03e

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Expected result:

ShellMicroPython

DE2120 ready. Press the button on the scanner to read a barcode.

Each code you scan then prints as Scanned: followed by the code's contents. When the scanner does not answer, the example prints DE2120 not detected. Check wiring. and stops.

Functions used

DE2120(uart=None, tx=None, rx=None, uart_id=1)returns DE2120

Creates the scanner object. Pass a UART you made yourself as uart, or pass tx and rx pin numbers and the module creates UART(uart_id) at 9600 baud on them. With neither, it raises ValueError.

ReturnsThe scanner object.

Parameters

Type	Name	Description
UART	uart	A ready machine.UART object. Optional.
int	tx	The controller pin that transmits, wired to the scanner's RX. The example uses 5.
int	rx	The controller pin that receives, wired to the scanner's TX. The example uses 4.
int	uart_id	Which UART to create when you pass tx and rx. 1 by default.

scanner.begin()returns bool

Checks that the scanner answers. It sets the UART to 9600 baud and asks for the firmware version. Without an answer it retries at 115200 baud, tells the scanner to switch to 9600 baud, and asks again. On success it empties the receive buffer.

ReturnsTrue when the scanner answered, False when it did not.

scanner.readBarcode()returns str or None

Collects the bytes waiting from the scanner. A scan ends with a carriage return; when one arrives, the function returns the code without it. Call it repeatedly in a loop. A single code keeps at most 256 bytes.

ReturnsThe scanned code, or None when no complete scan has arrived yet.

Putting it together

DE2120(tx=5, rx=4) sets up the UART, and begin() makes sure the scanner is there and running at 9600 baud. The loop then calls readBarcode() every 20 ms. It returns None until a whole code has arrived, so the if barcode: check prints each code once.

To read without pressing the button, see Read barcodes continuously.