Making a Barcode Scan Robot with Lego Boost and Webcam

If you want to quickly create a walking robot, you can use the Lego Boost. In this post, I will share how to use a webcam, Lego Boost, and Dynamsoft Barcode Reader SDK to make a robot for scanning barcodes. The programming language used in this article is Python.

How to Build the Robot with Lego Boost

To build the robot, install the Boost app and follow the relevant tutorials.

Python Programming Requirements

• Download Dynamsoft Barcode Reader for Linux. After extracting the package, copy libDynamsoftBarcodeReader.so to /usr/lib.
• Get a free 30-day trial license of Dynamsoft Barcode SDK.
• Get the source code of Dynamsoft Python barcode module and follow the steps to build and install.
• Install one of the Bluetooth backends:

  pip install pygatt
  pip install gatt
  pip install gattlib
  pip install bluepy

• Install pylgbst to interact with Lego Boost Move Hub:

  pip install https://github.com/undera/pylgbst/archive/1.0.tar.gz

• Install OpenCV Python:

  pip install opencv-python
  # or
  pip3 install opencv-python

How to Control Lego Boost Robot to Scan Barcodes

Create a camera view window using OpenCV:

    vc = cv2.VideoCapture(0)
    vc.set(3, 640) #set width
    vc.set(4, 480) #set height

    if vc.isOpened():  # try to get the first frame
        rval, frame = vc.read()
    else:
        return

    windowName = "Robot View"
    
    try:
        while True:
            rval, frame = vc.read()
            cv2.imshow(windowName, frame)

Due to GIL (Python Global Interpreter Lock), we need to run Bluetooth connection code and barcode decoding algorithm in another process rather than thread. All data, including key events, webcam frames, and barcode results, are transferred via Queue:

    num = Value('i', 1)
    result_queue = Queue(1)
    key_queue = Queue(1)
    frame_queue = Queue(1)
    cond = Condition()
    dbr_proc = Process(target=dbr_run, args=(
        frame_queue, key_queue, cond, num, result_queue))
    dbr_proc.start()

Here are the key definitions:

• a: left
• d: right
• w: up
• s: down
• q: terminate the app
• c: capture images and scan barcodes

The code for controlling the Lego Boost Robot is pretty simple. I use Gatt Backend:

conn GattConnection()  
try:
    conn.connect()
    hub = MoveHub(conn)
    print('Robot connected')
    speed = 0.5
                
    if key == ord('a'):
        # left
        hub.motor_AB.angled(90, speed * -1, speed)
    elif key == ord('d'):
        # right
        hub.motor_AB.angled(90, speed, speed * -1)
    elif key == ord('w'):
        # up                    
        hub.motor_AB.start_speed(speed)
    elif key == ord('s'):
        # down
        hub.motor_AB.start_speed(speed * -1)
    elif key == ord('p'):
        hub.motor_AB.stop()
finally:
    conn.disconnect()

Read the QR code and put the results into the queue:

dbr.initLicense('LICENSE-KEY')

if key == ord('c'):
    inputframe = frame_queue.get()
    results = dbr.decodeBuffer(inputframe, 0x4000000)
    if (len(results) > 0):
        for result in results:
            print("Type: " + result[0])
            print("Value: " + result[1] + "\n")

    result_queue.put(Result(inputframe, results))

Draw the barcode position and decoded text result using OpenCV:

                ret = result_queue.get_nowait()
                results = ret.results
                image = ret.image

                thickness = 2
                color = (0,255,0)
                for result in results:
                    print("barcode format: " + result[0])
                    print("barcode value: " + result[1])
                    x1 = result[2]
                    y1 = result[3]
                    x2 = result[4]
                    y2 = result[5]
                    x3 = result[6]
                    y3 = result[7]
                    x4 = result[8]
                    y4 = result[9]

                    cv2.line(image, (x1, y1), (x2, y2), color, thickness)
                    cv2.line(image, (x2, y2), (x3, y3), color, thickness)
                    cv2.line(image, (x3, y3), (x4, y4), color, thickness)
                    cv2.line(image, (x4, y4), (x1, y1), color, thickness)

                    cv2.putText(image, result[1], (min([x1, x2, x3, x4]), min([y1, y2, y3, y4])), cv2.FONT_HERSHEY_SIMPLEX, 1, (0,0,255), thickness)

                cv2.imshow("Localization", image)

Run the app:

python3 app.py

Source Code

https://github.com/yushulx/lego-boost-webcam-barcode

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