3.7 haas506 2.0开发教程-example-超声波测距

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1.JSN-SR04T超声波模块

(1)模块说明

- 规格参数

• 功能说明

• 模式0:Mode=悬空 高电平（PWM)脉宽输出
• 引脚定义

Pin	说明
Trig	触发控制引脚
Echo	高电平脉宽输出

(2)工作原理

  使用IO口Trig触发测距，至少给10us的高电平。模块自动发送8个40KHZ的方波，自动检测是否有信号返回。当有信号返回时，通过IO口Echo输出一个高电平，高电平持续的时间就是超声波从发射到返回的时间。常温下测试距离=(高电平时间*声速(348M/S))/2。模块被触发测距后，如果接收不到回波（原因超过所测范围或是探头没有正对被测物），ECHO 口会在 40MS 后自动变为低电平，标志着此次测量结束，不论成功与否。LED 上电时末亮，只有在给了 TRIG 引脚触发信号后才亮，灯闪频率与触发周期同步，说明此时模块接收到正确的指令进入工作状态。建议测量周期为 50ms 以上，以防止发射信号对回响信号的影响。
  简单来说就是主板通过IO口Trig给个不小于10us的高电平，触发测距。测距成功，模块通过IO口Echo输出一个高电平给主板；测距失败，ECHO 口会在 40MS 后自动结束本次测量。

• 其他模式可以百度一下，查看模块手册

2.测距

(1) 接线

JSN-SR04T超声波模块，有四个pin脚，分别是5V、GND、Trig、Echo。将这4个pin脚分别接入到haas506开发板上，io口可以自行定义。当前案例，将Trig接到了GPIO18，Echo接到了GPIO17，5v和GND接到了开发板的5V和GND上。
需要注意的是，5v脚接入到开发板电源3.3v或5v都行，但不能接入开发板的排母中的io口上。因为排母处的io口的输出电压为1.8V，电压低，无法触发测距。

(2) 代码

• main.py

#Import library
from driver import GPIO
import utime as time                       
#creat instances
TRIG = GPIO()                                  
ECHO = GPIO()                                 
TRIG.open('trig')             # Set pin as GPIO out
ECHO.open('echo')             # Set pin as GPIO in

def getData():
    TRIG.write(0)
    #set period,above 50ms
    time.sleep_ms(500)
    TRIG.write(1)                                #Set TRIG as LOW                                      
    time.sleep_us(10)                            #Delay of 10us
    TRIG.write(0)                                #Set TRIG as HIGH                               
    
    while ECHO.read()==0:                        #Check if Echo is LOW
        pass                 

    pulse_start = time.ticks_us()                #Time of the last  LOW pulse

    while ECHO.read()==1:                        #Check whether Echo is HIGH
        pass                  
    pulse_end = time.ticks_us()                  #Time of the last HIGH pulse 
    #print("pulse_duration",time.ticks_diff(pulse_end,pulse_start))     # us
    pulse_duration = time.ticks_diff(pulse_end,pulse_start)/10000      #pulse duration: s
    d=pulse_duration*340/2
    return d


if __name__=="__main__":
    try:
        while True:
            print ("-----measure distance test-----")
            if getData() > 20 and getData() < 600:
                print ("distance:%0.2f cm"  % getData())          
            else:
                print ("Out Of Range")    	   
    except KeyboardInterrupt:
        print("exit")

• board.json

{
    "name": "haas506",
    "version": "2.0.0",
    "io": {
      "ADC0": {
        "type": "ADC",
        "port": 0,
        "sampling": 12000000
      },
      "ADC1": {
        "type": "ADC",
        "port": 1,
        "sampling": 12000000
      },
      "qma8981": {
        "type": "I2C",
        "port": 1,
        "addrWidth": 7,
        "freq": 400000,
        "mode": "master",
        "devAddr": 18
      },
      "KEY1": {
        "type": "GPIO",
        "port": 44,
        "dir": "irq",
        "pull": "pullup",
        "intMode": "rising"
      },      
      "led1": {
        "type": "GPIO",
        "port": 7,
        "dir": "output",
        "pull": "pulldown"
      },
      "led_g": {
        "type": "GPIO",
        "port": 32,
        "dir": "output",
        "pull": "pulldown"
      },
      "cs": {
        "type": "GPIO",
        "port": 15,
        "dir": "output",
        "pull": "pullup"
      },
      "echo":{
        "type":"GPIO",
        "port": 17,
        "dir": "input",
        "pull":"pullup"
      },  
      "trig":{
        "type":"GPIO",
        "port": 18,
        "dir": "output",
        "pull":"pullup"
      },              
      "SPI0": {
        "type": "SPI",
        "port": 0,
        "mode": "master",
        "freq": 2000000
      },
      "serial1": {
        "type": "UART",
        "port": 0,
        "dataWidth": 8,
        "baudRate": 115200,
        "stopBits": 1,
        "flowControl": "disable",
        "parity": "none",
        "timeout": 1000
      },
      "serial2": {
        "type": "UART",
        "port": 1,
        "dataWidth": 8,
        "baudRate": 9600,
        "stopBits": 1,
        "flowControl": "disable",
        "parity": "none",
        "timeout": 1000
      },
      "serial3": {
        "type": "UART",
        "port": 2,
        "dataWidth": 8,
        "baudRate": 115200,
        "stopBits": 1,
        "flowControl": "disable",
        "parity": "none",
        "timeout": 1000
      }
    },
    "debugLevel": "ERROR",
    "repl": "enable",
    "replPort": 0
  }

3.效果

• 串口工具大概0.5s会更新一次当前测试的距离数据。
• 日志输出