Example explanation 17-Pixy-Emulation->AprilTags_Pixy_Uart_Emulation uses the Pixy UART protocol to transmit AprilTag

# 利用pixy uart协议传输apriltag
#
# 该脚本允许您的OpenMV Cam在spi模式下传输AprilTag检测数据，
# 就像Pixy（CMUcam5）跟踪颜色一样。 该脚本使您可以轻松地用
# OpenMV Cam AprilTag跟踪传感器替换Pixy（CMUcam5）颜色跟踪传感器。 
# 请注意，这只能在OpenMV Cam M7上运行。
#
# P4 = TXD
# P5 = RXD
#
# P7 = Servo 1
# P8 = Servo 2

# 注意：标签系列是TAG36H11。 此外，为了使标签检测的签名值与pixy 界面库兼容，
# 所有标签ID都添加了8个标签，以便将它们移动到颜色代码签名范围中。 # 最后，标签都被报告为颜色代码块。

# Pixy参数############################################################

max_blocks = 1000
max_blocks_per_id = 1000

uart_baudrate = 19200

# Pan Servo
s0_lower_limit = 1000 # 伺服脉冲宽度下限(以微秒计)。
s0_upper_limit = 2000 # 伺服脉冲宽度上限(微秒)。

# Tilt Servo
s1_lower_limit = 1000 # 伺服脉冲宽度下限(微秒)。
s1_upper_limit = 2000 # 伺服脉冲宽度上限(微秒)。

analog_out_enable = False # P6 -> Analog Out (0v - 3.3v).
analog_out_mode = 0 # 0 == x position of largest tag - 1 == y position of largest tag

##############################################################################

import image, math, pyb, sensor, struct, time

# 相机设置

sensor.reset()
sensor.set_pixformat(sensor.GRAYSCALE)
sensor.set_framesize(sensor.QQVGA)
sensor.skip_frames(time = 2000)

# LED设置

red_led = pyb.LED(1)
green_led = pyb.LED(2)
blue_led = pyb.LED(3)

red_led.off()
green_led.off()
blue_led.off()

# DAC设置

dac = pyb.DAC("P6") if analog_out_enable else None

if dac:
    dac.write(0)

# 舵机设置

min_s0_limit = min(s0_lower_limit, s0_upper_limit)
max_s0_limit = max(s0_lower_limit, s0_upper_limit)
min_s1_limit = min(s1_lower_limit, s1_upper_limit)
max_s1_limit = max(s1_lower_limit, s1_upper_limit)

s0_pan = pyb.Servo(1) # P7
s1_tilt = pyb.Servo(2) # P8

s0_pan.pulse_width(int((max_s0_limit - min_s0_limit) // 2)) # center
s1_tilt.pulse_width(int((max_s1_limit - min_s1_limit) // 2)) # center

s0_pan_conversion_factor = (max_s0_limit - min_s0_limit) / 1000
s1_tilt_conversion_factor = (max_s1_limit - min_s1_limit) / 1000

def s0_pan_position(value):
    s0_pan.pulse_width(round(s0_lower_limit + (max(min(value, 1000), 0) * s0_pan_conversion_factor)))

def s1_tilt_position(value):
    s1_tilt.pulse_width(round(s1_lower_limit + (max(min(value, 1000), 0) * s1_tilt_conversion_factor)))

# 链接设置

uart = pyb.UART(3, uart_baudrate, timeout_char = 1000)

def write(data):
    uart.write(data)

def available():
    return uart.any()

def read_byte():
    return uart.readchar()

# 辅助工作

def checksum(data):
    checksum = 0
    for i in range(0, len(data), 2):
        checksum += ((data[i+1] & 0xFF) << 8) | ((data[i+0] & 0xFF) << 0)
    return checksum & 0xFFFF

def to_object_block_format(tag):
    angle = int((tag.rotation() * 180) // math.pi)
    temp = struct.pack("<hhhhhh", tag.id() + 8, tag.cx(), tag.cy(), tag.w(), tag.h(), angle)
    return struct.pack("<hh12s", 0xAA56, checksum(temp), temp)

# FSM 代码

fsm_state = 0
last_byte = 0

FSM_STATE_NONE = 0
FSM_STATE_ZERO = 1
FSM_STATE_SERVO_CONTROL_0 = 2
FSM_STATE_SERVO_CONTROL_1 = 3
FSM_STATE_SERVO_CONTROL_2 = 4
FSM_STATE_SERVO_CONTROL_3 = 5
FSM_STATE_CAMERA_CONTROL = 6
FSM_STATE_LED_CONTROL_0 = 7
FSM_STATE_LED_CONTROL_1 = 8
FSM_STATE_LED_CONTROL_2 = 9

def parse_byte(byte):
    global fsm_state
    global last_byte

    if fsm_state == FSM_STATE_NONE:
        if byte == 0x00: fsm_state = FSM_STATE_ZERO
        else: fsm_state = FSM_STATE_NONE

    elif fsm_state == FSM_STATE_ZERO:
        if byte == 0xFF: fsm_state = FSM_STATE_SERVO_CONTROL_0
        elif byte == 0xFE: fsm_state = FSM_STATE_CAMERA_CONTROL
        elif byte == 0xFD: fsm_state = FSM_STATE_LED_CONTROL_0
        else: fsm_state = FSM_STATE_NONE

    elif fsm_state == FSM_STATE_SERVO_CONTROL_0:
        fsm_state = FSM_STATE_SERVO_CONTROL_1

    elif fsm_state == FSM_STATE_SERVO_CONTROL_1:
        fsm_state = FSM_STATE_SERVO_CONTROL_2
        s0_pan_position(((byte & 0xFF) << 8) | ((last_byte & 0xFF) << 0))

    elif fsm_state == FSM_STATE_SERVO_CONTROL_2:
        fsm_state = FSM_STATE_SERVO_CONTROL_3

    elif fsm_state == FSM_STATE_SERVO_CONTROL_3:
        fsm_state = FSM_STATE_NONE
        s1_tilt_position(((byte & 0xFF) << 8) | ((last_byte & 0xFF) << 0))

    elif fsm_state == FSM_STATE_CAMERA_CONTROL:
        fsm_state = FSM_STATE_NONE
        # 忽略……

    elif fsm_state == FSM_STATE_LED_CONTROL_0:
        fsm_state = FSM_STATE_LED_CONTROL_1
        if byte & 0x80: red_led.on()
        else: red_led.off()

    elif fsm_state == FSM_STATE_LED_CONTROL_1:
        fsm_state = FSM_STATE_LED_CONTROL_2
        if byte & 0x80: green_led.on()
        else: green_led.off()

    elif fsm_state == FSM_STATE_LED_CONTROL_2:
        fsm_state = FSM_STATE_NONE
        if byte & 0x80: blue_led.on()
        else: blue_led.off()

    last_byte = byte

# 主循环

clock = time.clock()
while(True):
    clock.tick()
    img = sensor.snapshot()
    tags = img.find_apriltags() # default TAG36H11 family

    # 传输标签 #

    if tags and (max_blocks > 0) and (max_blocks_per_id > 0): # new frame
        dat_buf = struct.pack("<h", 0xAA55)
        id_map = {}
        first_b = False

        for tag in sorted(tags, key = lambda x: x.area(), reverse = True)[0:max_blocks]:

            if not tag.id() in id_map:
                id_map[tag.id()] = 1
            else:
                id_map[tag.id()] += 1

            if id_map[tag.id()] <= max_blocks_per_id:
                dat_buf += to_object_block_format(tag)
                img.draw_rectangle(tag.rect())
                img.draw_cross(tag.cx(), tag.cy())

            if dac and not first_b:
                x_scale = 255 / (img.width()-1)
                y_scale = 255 / (img.height()-1)
                dac.write(round((tag.y() * y_scale) if analog_out_mode else (tag.x() * x_scale)))
                first_b = True

        dat_buf += struct.pack("<h", 0x0000)
        write(dat_buf) # 把所有数据写在一个包里…

    else: # 没有发现
        write(struct.pack("<h", 0x0000))

        if dac:
            dac.write(0)

    # 解析命令 #

    for i in range(available()):
        parse_byte(read_byte())

    num_tags = min(len(tags), max_blocks)
    print("%d tags(s) found - FPS %f" % (num_tags, clock.fps()))

Singtown Technology OpenMV official Chinese document function explanation: