Example Code for Raspberry Pi-Distance Measurement

Hardware Preparation

• Raspberry Pi 4B
• Raspberry Pi IO Expansion Board
• A01NYUB Ultrasonic Sensor
• 4P Connector

Software Preparation

• Raspberry Pi OS
• Python 3 (included with Raspberry Pi OS)
• serial library (install via pip install pyserial)
• Ultrasonic Sensor Library

Wiring Diagram

Other Preparation Work

1. Enable UART on Raspberry Pi (follow Raspberry Pi UART Setup Guide).
2. Install the required serial library via pip install pyserial.
3. Download and install the Ultrasonic Sensor Library.

Sample Code

Download the Ultrasonic Sensor Library

# -*- coding:utf-8 -*-

'''!
  @file DFRobot_RaspberryPi_A02YYUW.py
  @brief Ranging distance sensor。
  @copyright   Copyright (c) 2010 DFRobot Co.Ltd (http://www.dfrobot.com)
  @license     The MIT License (MIT)
  @author      Arya([email protected])
  @version     V1.0
  @date        2021-08-30
  @url https://github.com/DFRobot/DFRobot_RaspberryPi_A02YYUW
'''

import serial

import time

class DFRobot_A02_Distance:

  ## Board status 
  STA_OK = 0x00
  STA_ERR_CHECKSUM = 0x01
  STA_ERR_SERIAL = 0x02
  STA_ERR_CHECK_OUT_LIMIT = 0x03
  STA_ERR_CHECK_LOW_LIMIT = 0x04
  STA_ERR_DATA = 0x05

  ## last operate status, users can use this variable to determine the result of a function call. 
  last_operate_status = STA_OK

  ## variable 
  distance = 0

  ## Maximum range
  distance_max = 4500
  distance_min = 0
  range_max = 4500

  def __init__(self):
    '''
      @brief    Sensor initialization.
    '''
    self._ser = serial.Serial("/dev/ttyAMA0", 9600)
    if self._ser.isOpen() != True:
      self.last_operate_status = self.STA_ERR_SERIAL

  def set_dis_range(self, min, max):
    self.distance_max = max
    self.distance_min = min

  def getDistance(self):
    '''
      @brief    Get measured distance
      @return    measured distance
    '''
    self._measure()
    return self.distance
  
  def _check_sum(self, l):
    return (l[0] + l[1] + l[2])&0x00ff

  def _measure(self):
    data = [0]*4
    i = 0
    timenow = time.time()

    while (self._ser.inWaiting() < 4):
      time.sleep(0.01)
      if ((time.time() - timenow) > 1):
        break
    
    rlt = self._ser.read(self._ser.inWaiting())
    #print(rlt)
    
    index = len(rlt)
    if(len(rlt) >= 4):
       index = len(rlt) - 4
       while True:
         try:
           data[0] = ord(rlt[index])
         except:
           data[0] = rlt[index]
         if(data[0] == 0xFF):
           break
         elif (index > 0):
           index = index - 1
         else:
           break
       #print(data)
       if (data[0] == 0xFF):
         try:
           data[1] = ord(rlt[index + 1])
           data[2] = ord(rlt[index + 2])
           data[3] = ord(rlt[index + 3])
         except:
           data[1] = rlt[index + 1]
           data[2] = rlt[index + 2]
           data[3] = rlt[index + 3]
         i = 4
    #print(data)
    if i == 4:
      sum = self._check_sum(data)
      if sum != data[3]:
        self.last_operate_status = self.STA_ERR_CHECKSUM
      else:
        self.distance = data[1]*256 + data[2]
        self.last_operate_status = self.STA_OK
      if self.distance > self.distance_max:
        self.last_operate_status = self.STA_ERR_CHECK_OUT_LIMIT
        self.distance = self.distance_max
      elif self.distance < self.distance_min:
        self.last_operate_status = self.STA_ERR_CHECK_LOW_LIMIT
        self.distance = self.distance_min
    else:
      self.last_operate_status = self.STA_ERR_DATA
    return self.distance