这个是arduino接受数据的

int LED = 13;
int i=0,p=0,m=0;
void setup()
{
  Serial.begin(115200);//模块上电灯快闪，arduino发送指令时需要按住模块上的按键
 pinMode(LED,OUTPUT);
}
void loop()
{
    char ch;
    ch = Serial.read();
   Serial.print(ch);
//   if(ch=='C')
//   {
//        digitalWrite(LED,HIGH);
//         delay(100);
//   }
  delay(40);
//   digitalWrite(LED,LOW);
}

这个是openmv测距然后加了串口发送

# Measure the distance
#
# This example shows off how to measure the distance through the size in imgage
# This example in particular looks for yellow pingpong ball.

import sensor, image, time

from pyb import UART

uart = UART(3, 115200)
uart.init(115200, bits=8, parity=None, stop=1) # init with given parameters

# For color tracking to work really well you should ideally be in a very, very,
# very, controlled enviroment where the lighting is constant...
yellow_threshold   = ( 56,   83,    5,   57,   63,   80)
# You may need to tweak the above settings for tracking green things...
# Select an area in the Framebuffer to copy the color settings.

sensor.reset() # Initialize the camera sensor.
sensor.set_pixformat(sensor.RGB565) # use RGB565.
sensor.set_framesize(sensor.QQVGA) # 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.

K=5000#the value should be measured

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

    blobs = img.find_blobs([yellow_threshold])
    if len(blobs) == 1:
        # Draw a rect around the blob.
        b = blobs[0]
        img.draw_rectangle(b[0:4]) # rect
        img.draw_cross(b[5], b[6]) # cx, cy
        Lm = (b[2]+b[3])/2
        length = K/Lm
        output_str="[%d,%d]" % (b[5],b[6]) #方式1
        #output_str=json.dumps([max_blob.cx(),max_blob.cy()]) #方式2
        uart.write(output_str+'\r\n')
        print(b[5],b[6])

    #print(clock.fps()) # Note: Your OpenMV Cam runs about half as fast while
    # connected to your computer. The FPS should increase once disconnected.

说明，问号是没有发送数据时的显示。问题：接受数据的前面的几个数据正常，为什么后面的就不对了？求解