串口通信上

视频教程27 - 串口通信发送数据:https://singtown.com/learn/50235/

视频教程28 - 串口通信接收数据:https://singtown.com/learn/50240/

介绍

为什么要用串口呢?因为要时候需要把信息传给其他MCU,串口简单,通用,基本每一个MCU都会有串口。

TTL串口至少需要3根线:TXD,RXD,GND。TXD是发送端,RXD是接收端,GND是地线。 连线的时候,需要把OpenMV的RXD连到另一个MCU的TXD,TXD连到RXD。图示:

import time
from pyb import UART

uart = UART(3, 19200)

while(True):
    uart.write("Hello World!\r")
    time.sleep(1000)

先实例化一个19200波特率的串口3,然后调用write方法就可以了。
注意:必须是串口3,因为OpenMV2只引出了这个串口,pyb的串口有好多个的。OpenMV3又增加了串口1。

传输复杂的数据

在前一节说过json字符串。

# Blob Detection and uart transport
import sensor, image, time
from pyb import UART
import json
# 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   = (65, 100, -10, 6, 24, 51)
# 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.

uart = UART(3, 115200)

while(True):
    img = sensor.snapshot() # Take a picture and return the image.

    blobs = img.find_blobs([yellow_threshold])
    if blobs:
        print('sum :', len(blobs))
        output_str = json.dumps(blobs)
        for b in blobs:
            # Draw a rect around the blob.
            img.draw_rectangle(b.rect()) # rect
            img.draw_cross(b.cx(), b.cy()) # cx, cy

        print('you send:',output_str)
        uart.write(output_str+'\n')
    else:
        print('not found!')

结果的输出为:

sum : 1
you send: [{x:17, y:23, w:37, h:12, pixels:178, cx:40, cy:29, rotation:3.060313, code:1, count:1}]
sum : 2
you send: [{x:34, y:24, w:19, h:13, pixels:149, cx:45, cy:30, rotation:3.120370, code:1, count:1}, {x:23, y:30, w:8, h:2, pixels:17, cx:27, cy:30, rotation:0.046378, code:1, count:1}]

这样就把整个blobs全部发送出去了。

精简数据

但是有时候不想传输一大堆的数据。比如:我只想传输面积最大的色块的x,y中心坐标。
想传输什么数据,就构造一个什么数据。

写一个for循环,再写一个find_max()函数。

# Blob Detection and uart transport
import sensor, image, time
from pyb import UART
import json
# 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   = (65, 100, -10, 6, 24, 51)
# 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.

uart = UART(3, 115200)
def find_max(blobs):
    max_size=0
    for blob in blobs:
        if blob.pixels() > max_size:
            max_blob=blob
            max_size = blob.pixels()
    return max_blob

while(True):
    img = sensor.snapshot() # Take a picture and return the image.

    blobs = img.find_blobs([yellow_threshold])
    if blobs:
        max_blob=find_max(blobs)
        print('sum :', len(blobs))
        img.draw_rectangle(max_blob.rect())
        img.draw_cross(max_blob.cx(), max_blob.cy())

        output_str="[%d,%d]" % (max_blob.cx(),max_blob.cy()) #方式1
        #output_str=json.dumps([max_blob.cx(),max_blob.cy()]) #方式2
        print('you send:',output_str)
        uart.write(output_str+'\r\n')
    else:
        print('not found!')

结果:

sum : 6
you send: [63,45]
sum : 2
you send: [60,50]
sum : 1
you send: [61,51]

在上面的代码中,

output_str="[%d,%d]" % (max_blob.cx(),max_blob.cy()) #方式1

output_str=json.dumps([max_blob.cx(),max_blob.cy()]) #方式2

的结果是一样的,因为结构简单,可以使用python的字符串格式化的功能,或者json的转换功能,都可以。

结果中,即使找到了多个色块,也只发送最大的色块的坐标。

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