4. NameError:local variable referenced before assignment
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    • NameError:local variable referenced before assignment

    • C
       

      import sensor,image, time
from servo import Servos
from pid import PID
from machine import I2C, Pin

i2c = I2C(sda=Pin('P5'), scl=Pin('P4'))
tilt_servo = Servos(i2c, address=0x40, freq=50, min_us=500, max_us=2500, degrees=180) #通道1
pan_servo = Servos(i2c, address=0x40, freq=50, min_us=500, max_us=2500, degrees=180)  #通道2


red_threshold  = (46, 57, 46, 72, 9, 51)

#pan_pid = PID(p=0.02, i=0, imax=90,d=0.001) #脱机运行或者禁用图像传输，使用这个PID
#tilt_pid = PID(p=0.019, i=0, imax=90,d=0.001) #脱机运行或者禁用图像传输，使用这个PID
pan_pid = PID (p=0.018, i=0, imax=90,d=0)#在线调试使用这个PID
tilt_pid = PID(p=0.018, i=0, imax=90,d=0)#在线调试使用这个PID
pan=50#X初角度  70
tilt=50#Y初角度 50
pan_servo.position(1, pan)
tilt_servo.position(0,tilt)
sensor.reset() # Initialize the camera sensor.
sensor.set_pixformat(sensor.RGB565) # use RGB565.
sensor.set_hmirror(True)
sensor.set_vflip(True)
sensor.set_framesize(sensor.QVGA) # use QQVGA for speed.
sensor.skip_frames(10) # Let new settings take affect.
sensor.set_auto_whitebal(False) # turn this off.

clock = time.clock() # Tracks FPS.

# blob[2]=blob.width
# blob[3]=blob.height
def find_max(blobs):
    max_size=0
    for blob in blobs:
        ratio = blob[2] / blob[3]
        if (ratio >= 0.7) and (ratio <= 1.3):
            if (blob[2]*blob[3] > max_size):
                max_blob=blob
                max_size = blob[2]*blob[3]
    return max_blob


while(True):
    clock.tick() # Track elapsed milliseconds between snapshots().
    img = sensor.snapshot() # Take a picture and return the image.

    blobs = img.find_blobs([red_threshold])
    if blobs:
        max_blob = find_max(blobs)
        pan_error = max_blob.cx()-img.width()/2
        tilt_error = max_blob.cy()-img.height()/2

        print("pan_error: ", pan_error)

        img.draw_rectangle(max_blob.rect()) # rect=返回一个矩形元组(x, y, w, h)
        img.draw_cross(max_blob.cx(), max_blob.cy()) # cx, cy 画一个十字

        pan_output=pan_pid.get_pid(pan_error,1)
        tilt_output=tilt_pid.get_pid(tilt_error,1)
        print("pan_output",pan_output)
        pan_servo.position(1, pan-pan_output)
        tilt_servo.position(0,tilt+tilt_output)
        pan=pan-pan_output
        tilt=tilt+tilt_output
        print(clock.fps())
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    • 如果你的blobs是空的就会出现，写一个if判断一下。

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