M5Stack Unit2 switch mode by sending command in serial port

  • Hi there,

    I'm trying to manage UnitV2 device by Serial port. Reading data works just fine, for example in the "Object detection" mode Unit sends data:

    {'num': 1, 'obj': [{'prob': 0.697403133, 'x': 44, 'y': 8, 'w': 555, 'h': 466, 'type': 'person'}], 'running': 'Object Recognition'}
    {'num': 1, 'obj': [{'prob': 0.684900761, 'x': 49, 'y': 1, 'w': 543, 'h': 468, 'type': 'person'}], 'running': 'Object Recognition'}
    {'num': 1, 'obj': [{'prob': 0.686426222, 'x': 23, 'y': 2, 'w': 577, 'h': 472, 'type': 'person'}], 'running': 'Object Recognition'}

    Unfortunately I can't manage to send commands and actually switch the mode. Here is my code for Raspberry PI(connected with UnitV2 by serial ports):

    import serial, json
    with serial.Serial() as s:
        s.port = '/dev/ttyAMA0'
        s.baudrate = 115200
        s.timeout = .5
        js = {
            'function': 'Camera Stream',
            'args': ''
        print("send", js)
        response = s.readline()
        print("receive", response)

    And the output:

    send {'function': 'Camera Stream', 'args': ''}
    receive b''

    Am I missing something?

  • Finally I managed to switch the mode from Raspberry PI using ReaderThread. Here is the code:

    import sys
    import traceback
    import argparse
    import json
    import serial
    from serial.threaded import LineReader, ReaderThread
    from time import sleep
    MODES = [
        'Audio FFT',
        'Code Detector',
        'Face Detector',
        'Lane Line Tracker',
        'Motion Tracker',
        'Shape Matching',
        'Camera Stream',
        'Online Classifier',
        'Color Tracker',
        'Face Recognition',
        'Target Tracker',
        'Shape Detector',
        'Object Recognition',
    ap = argparse.ArgumentParser()
    ap.add_argument('-m', '--mode', help = 'Switch to mode: {}'.format(MODES))
    ap.add_argument('-a', '--args', default = '', help = 'Some modes require extra args. For "Object Recognition" either "yolo_20class" or "nanodet_80class"')
    args = vars(ap.parse_args())
    if 'mode' not in args or args['mode'] not in MODES:
    if args['mode'] == 'Object Recognition' and args['args'] not in OBJECT_RECOGNITION_ARGS:
    class PrintLines(LineReader):
        def connection_made(self, transport):
            super(PrintLines, self).connection_made(transport)
            sys.stdout.write('port opened\n')
        def handle_line(self, data):
            sys.stdout.write('line received: {}\n'.format(repr(data)))
        def connection_lost(self, exc):
            if exc:
            sys.stdout.write('port closed\n')
    with serial.Serial() as s:
        s.port = '/dev/ttyAMA0'
        s.baudrate = 115200
        s.timeout = .5
        with ReaderThread(s, PrintLines) as protocol:
            js = {
                'function': args['mode'],
                'args': args['args']

    And the output:

    pi@rpi0:~/serial$ ./serial_mode.py --mode 'Object Recognition' --args 'yolo_20class'
    port opened
    line received: '{"msg":"function switched to object_recognition."}'
    line received: '{"msg":"Running Object Recognition, Copyright 2021 M5Stack Technology Co., Ltd. All rights reserved.","running":"Object Recognition"}'
    port closed

  • Hi Odemakov
    Any way you can just provide the actual string sent for any one of the functions?
    I am not using Python and have a hard time parsing what the code produces as a json string that is sent to V2.

  • I would like to send command to change unit v2 to code dectector by arduino when m5 Stack power on. Please give me sample code. Thank you.

  • Getting closer... This is the string to change modes.

    Function switch
    Switch between different recognition functions by clicking the navigation bar of the function page or sending JSON commands through Serial Port communication. Note: Except at the end of the sent command string, no line breaks are allowed in other positions.

    "function": "Camera Stream",
    "args": ""

    BUT this is what I get in return

    {"error":"invalid json format."}
    {"error":"invalid json format."}
    {"error":"invalid json format."}
    {"error":"invalid json format."}
    {"error":"Command is not supported"}
    {"error":"invalid json format."}
    {"error":"invalid json format."}

    Anyone have any ideas?
    I'm sending the string through a serial termanal. CR,LF