arduino
Comunicazione I2C

introduzione

Schiavi multipli

L'esempio seguente mostra come il master può ricevere dati da più slave. In questo esempio lo slave invia due numeri brevi. Il primo è per la temperatura e il secondo per l'umidità. Si prega di notare che la temperatura è un galleggiante (24.3). Per utilizzare solo due byte e non quattro (float è quattro byte), ho più volte la temperatura in 10, e lo salvo come un breve. Quindi ecco il codice principale:

#include <Wire.h>

#define BUFFER_SIZE  4
#define MAX_NUMBER_OF_SLAVES 24
#define FIRST_SLAVE_ADDRESS 1
#define READ_CYCLE_DELAY 1000

byte buffer[BUFFER_SIZE];

void setup()
{
  Serial.begin(9600);  
  Serial.println("MASTER READER");
  Serial.println("*************");
  
  Wire.begin();        // Activate I2C link
}

void loop()
{
  for (int slaveAddress = FIRST_SLAVE_ADDRESS; 
       slaveAddress <= MAX_NUMBER_OF_SLAVES; 
       slaveAddress++) 
  { 
    Wire.requestFrom(slaveAddress, BUFFER_SIZE);    // request data from the slave
    if(Wire.available() == BUFFER_SIZE)
      {  // if the available data size is same as I'm expecting
        // Reads the buffer the slave sent
        for (int i = 0; i < BUFFER_SIZE; i++) 
        {
          buffer[i] = Wire.read();  // gets the data
        }

        // Parse the buffer
        // In order to convert the incoming bytes info short, I use union
        union short_tag {
          byte b[2];
          short val;
        } short_cast;

        // Parse the temperature
        short_cast.b[0] = buffer[0];
        short_cast.b[1] = buffer[1];
        float temperature = ((float)(short_cast.val)) / 10;

        // Parse the moisture
        short_cast.b[0] = buffer[2];
        short_cast.b[1] = buffer[3];
        short moisture = short_cast.val;

        // Prints the income data
        Serial.print("Slave address ");      
        Serial.print(slaveAddress);
        Serial.print(": Temprature = ");
        Serial.print(temprature);
        Serial.print("; Moisture = ");
        Serial.println(moisture);
      }
    }
    Serial.println("*************************");
  
    delay(READ_CYCLE_DELAY);
  }
}

E ora il codice slave:

#include <Wire.h>
#include <OneWire.h>
#include <DallasTemperature.h>

//=====================
// This is the hard-coded address. Change it from one device to another
#define SLAVE_ADDRESS 1
//=====================

// I2C Variables
#define BUFFER_SIZE 2
#define READ_CYCLE_DELAY 1000
short data[BUFFER_SIZE];

// Temprature Variables
OneWire oneWire(8);
DallasTemperature temperatureSensors(&oneWire);
float m_temperature;

// Moisture Variables
short m_moisture;

// General Variables
int m_timestamp;

void setup()
{
  Serial.begin(9600);  
  Serial.println("SLAVE SENDER");
  Serial.print("Node address: ");
  Serial.println(SLAVE_ADDRESS);
  Serial.print("Buffer size: ");
  Serial.println(BUFFER_SIZE * sizeof(short));
  Serial.println("***********************");

  m_timestamp = millis();
  Wire.begin(NODE_ADDRESS);  // Activate I2C network
  Wire.onRequest(requestEvent); // Set the request event handler
  temperatureSensors.begin();
}

void loop()
{ 
  if(millis() - m_timestamp < READ_CYCLE_DELAY) return;

  // Reads the temperature
  temperatureSensors.requestTemperatures();
  m_temperature = temperatureSensors.getTempCByIndex(0);

  // Reads the moisture
  m_moisture = analogRead(A0);
}

void requestEvent()
{
  data[0] = m_temperature * 10; // In order to use short, I multiple by 10
  data[1] = m_moisture;
  Wire.write((byte*)data, BUFFER_SIZE * sizeof(short));  
}