Practical use of ultrasonic Sensor with ATMEGA328P and Raspberry PI

Practical use of Ultrasonic Sensor SR04 with ATMEGA328P and Raspberry PI

Introduction

I2C is a two-wire bus that is designed to be simple, reliable, and energy-efficient. It is often used to connect microcontrollers, sensors, and other peripherals. I2C is also widely used for communication between microcontrollers and external memory.

In this article, we present an alternative to directly using the Raspberry PI GPio to control external devices. I2C makes it possible to consume external data using this communication method. We use an Arduino UNO as a slave I2C device, controlling the HC-SR04 Ultrasonic Sensor, and a Raspberry PI B+ as a master I2C device, consuming the Sensor Data. In addition, the code for both the ATMEGA328P and Raspberry PI B+ has been included.

Connection Diagram

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Raspberry as I2C Master Code

#!/usr/bin/env python
​
from smbus2 import SMBus, i2c_msg
import time
import struct
​
# bus = smbus.SMBus(1)
​
address = 0x0A
​
def read_float_from_arduino(address):
    with SMBus(1) as bus:
        b = []
        for _ in range(4):
            b.append(bus.read_byte(address))
        f = struct.unpack('f', bytearray(b))
        # print([hex(n) for n in b])
        # print("{0:4f}".format(f[0]))
        return f[0] 
​
​
if __name__ == '__main__':
    bus = SMBus(1)
    try:
        while True:
            float_value = read_float_from_arduino(address)
            print("{0:3f} cms".format(float_value))
            time.sleep(0.25)
    except KeyboardInterrupt:
        pass
​

ATMEGA328P as I2C Slave Code

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#include <Wire.h>
​
#define I2C_SLAVE_ADDRESS 10 // I2C Id Address
#define TRIGGER 2    //Digital Pin for Sensor Trigger
#define ECHO    3    //Digital Pin for Sensor Echo
#define LEDPIN  13   //General Purpose LED
​
union FloatUnion {
    float number;
    uint8_t bytes[4];
} dataToSend;
​
int byteCount = 0;
int sampleSize = 5;
​
​
void setup() {
  Wire.begin(I2C_SLAVE_ADDRESS);
  Serial.begin(9600);
  delay(1000);
  
  // Setup HC-SR04 Sensor 
  pinMode(TRIGGER, OUTPUT);   //Setup TRIGGER as output
  pinMode(ECHO, INPUT);       //Setup ECHO as input
  digitalWrite(TRIGGER, LOW); //Init TRIGGER with 0
  
  // Setup Send and Receive I2C Interrupt Methods  
  Wire.onRequest(requestEvent);
  Wire.onReceive(receiveEvent);
​
  Serial.println("--------- Arduino Configure as Slave on I2C ----------");
  dataToSend.number = retrieveAvgMeasureSample(sampleSize);
}
​
​
void loop() {
  //Serial.println(retrieveAvgMeasureSample(3));
  dataToSend.number = retrieveAvgMeasureSample(sampleSize);
  delay(10);  
}
​
/*
 * 
 */
float retrieveSingleMeasure(){
  long  echoTime;     //Time length for echo retrieving
  float distance;     //Distance in cms
  // Send 10us duration pulse
  digitalWrite(TRIGGER, HIGH);
  delayMicroseconds(10);          //Enviamos un pulso de 10us
  digitalWrite(TRIGGER, LOW);
​
  echoTime = pulseIn(ECHO, HIGH); //Retrive the echo pulse width
  distance = echoTime/59;         //Time scaling for a particular distance in cms
  
  delay(100);  //Pause for 100ms
  return  distance;
}
​
​
/**
 * 
 */
float retrieveAvgMeasureSample(int sampleSize) {
  float currentSample = 0;
  for(int nSample = 0; nSample < sampleSize; nSample++)
     currentSample += retrieveSingleMeasure();
  return currentSample/sampleSize; 
}
​
​
/**
 * 
 */
void requestEvent(){    
  for(int i = 0; i < 4; i++){
    Serial.print(dataToSend.bytes[i], HEX);
    Serial.print(" ");
  }
  Serial.println("");
  //
  Wire.write(dataToSend.bytes[byteCount++]);
  if (byteCount == 4) byteCount=0;
}
​
​
/**
 * 
 */
void receiveEvent(int numBytes) {
  for(int i = 0; i < numBytes; i++){
    byte byteReceived = Wire.read();
    Serial.print(byteReceived, HEX);
    Serial.print(" ");
  }
​
  Serial.println("");
}