在树莓派上测试防水型超声波测距模块
当我们需要测量水桶里的水位或者在室外环境下进行距离测量时,那么会用到防水的超声波测距模块。它的使用与普通的超声波模块 HC-SR04 的方式是相同的。
防水型超声波传感器模块

是不是和我们常见的倒车雷达的探头是一样的。没错倒车雷达也就是在室外环境下使用的防水型超声波测距模块。除了上面的探头外,它还有一个控制板。


这个控制板的4个引脚功能与HR-SR04模块一样,分别是: Trigger (触发)、 Echo 、5V和GND, 模块能提供25厘米- 450厘米之间的测量范围。
超声波传感器模块与树莓派的连接
本文中,超声波模块直接从树莓派的5V和GND引脚取电,对应树莓派R1版是Pin 2和Pin 6引脚。超声波模块上的输入引脚称为“触发端”,用于发送超声波脉冲。它可以在树莓派GPIO引脚3.3V电压下很好的工作,所以模块的触发端 Trigger 引脚直接可以连接到树莓派R1版的引脚16 (GPIO23)。
该模块的输出脚称为“echo”,输出引脚默认是低电平状态(0V),当模块开始进行距离测量后,它进入高电平状态。这个引脚的高电平持续时间与脉冲返回的时间是相同的。所以我们的代码需要测量这个引脚保持高电平状态的时间。模块使用+5V电平表示“高电平”,但是对于树莓派上GPIO引脚的电压值来说太高了,GPIO引脚只能是3.3V。为了确保树莓派的安全,我们可以使用一个由两个电阻组成的简单分压器。

由两个电阻组成的简单分压器。
如果R1和R2相等,则电压平分,这就得到2.5v电压。如果R2是R1的两倍那么就可以得到约3.33v电压。理想情况下,R2的值应该在R1和R1 x2之间。在示例电路中,使用了330欧和470欧的电阻。另外也可以使用使用1K和1.5K电阻。
下面是最终的电路连接图。使用了GPIO23和GPIO24,也可以使用其他的GPIO引脚,需要记住相应的引脚编号并在Python脚本中更新即可。

Python脚本
这里提供了两个测试脚本。分别是只读取一次测量数据和连续读取测量数据,详细如下:
一、读取一次测量数据并以厘米为单位显示结果:
#!/usr/bin/python # ----------------------- # Import required Python libraries from __future__ import print_function import time import RPi.GPIO as GPIO # Use BCM GPIO references # instead of physical pin numbers GPIO.setmode(GPIO.BCM) # Define GPIO to use on Pi GPIO_TRIGGER = 23 GPIO_ECHO = 24 # Speed of sound in cm/s at temperature temperature = 20 speedSound = 33100 + (0.6*temperature) print("Ultrasonic Measurement") print("Speed of sound is",speedSound/100,"m/s at ",temperature,"deg") # Set pins as output and input GPIO.setup(GPIO_TRIGGER,GPIO.OUT) # Trigger GPIO.setup(GPIO_ECHO,GPIO.IN) # Echo # Set trigger to False (Low) GPIO.output(GPIO_TRIGGER, False) # Allow module to settle time.sleep(0.5) # Send 10us pulse to trigger GPIO.output(GPIO_TRIGGER, True) # Wait 10us time.sleep(0.00001) GPIO.output(GPIO_TRIGGER, False) start = time.time() while GPIO.input(GPIO_ECHO)==0: start = time.time() while GPIO.input(GPIO_ECHO)==1: stop = time.time() # Calculate pulse length elapsed = stop-start # Distance pulse travelled in that time is time # multiplied by the speed of sound (cm/s) distance = elapsed * speedSound # That was the distance there and back so halve the value distance = distance / 2 print("Distance : {0:5.1f}".format(distance)) # Reset GPIO settings GPIO.cleanup()
二、连续读取测量数据并以厘米为单位显示结果:
#!/usr/bin/python # ----------------------- # Import required Python libraries # ----------------------- from __future__ import print_function import time import RPi.GPIO as GPIO # ----------------------- # Define some functions # ----------------------- def measure(): # This function measures a distance GPIO.output(GPIO_TRIGGER, True) # Wait 10us time.sleep(0.00001) GPIO.output(GPIO_TRIGGER, False) start = time.time() while GPIO.input(GPIO_ECHO)==0: start = time.time() while GPIO.input(GPIO_ECHO)==1: stop = time.time() elapsed = stop-start distance = (elapsed * speedSound)/2 return distance def measure_average(): # This function takes 3 measurements and # returns the average. distance1=measure() time.sleep(0.1) distance2=measure() time.sleep(0.1) distance3=measure() distance = distance1 + distance2 + distance3 distance = distance / 3 return distance # ----------------------- # Main Script # ----------------------- # Use BCM GPIO references # instead of physical pin numbers GPIO.setmode(GPIO.BCM) # Define GPIO to use on Pi GPIO_TRIGGER = 23 GPIO_ECHO = 24 # Speed of sound in cm/s at temperature temperature = 20 speedSound = 33100 + (0.6*temperature) print("Ultrasonic Measurement") print("Speed of sound is",speedSound/100,"m/s at ",temperature,"deg") # Set pins as output and input GPIO.setup(GPIO_TRIGGER,GPIO.OUT) # Trigger GPIO.setup(GPIO_ECHO,GPIO.IN) # Echo # Set trigger to False (Low) GPIO.output(GPIO_TRIGGER, False) # Allow module to settle time.sleep(0.5) # Wrap main content in a try block so we can # catch the user pressing CTRL-C and run the # GPIO cleanup function. This will also prevent # the user seeing lots of unnecessary error # messages. try: while True: distance = measure_average() print("Distance : {0:5.1f}".format(distance)) time.sleep(1) except KeyboardInterrupt: # User pressed CTRL-C # Reset GPIO settings GPIO.cleanup()
专题:超声波测距模块:
- HC-SR04超声波测距模块的测试
- SRF02超声波测距模块的连接
- KS103测距模块很牛
- 在树莓派上测试防水型超声波测距模块