arduino
I2C-Kommunikation

Einführung

Mehrere Sklaven

Das folgende Beispiel zeigt, wie der Master Daten von mehreren Slaves empfangen kann. In diesem Beispiel sendet der Slave zwei kurze Nummern. Der erste ist für die Temperatur und der zweite für die Feuchtigkeit. Bitte beachten Sie, dass es sich bei der Temperatur um einen Schwimmer handelt (24.3). Um nur zwei und nicht vier Byte zu verwenden (Float ist vier Bytes), multipliziere ich die Temperatur in 10 und speichere es als Kurzform. Also hier ist der Mastercode:

#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);
  }
}

Und nun der Sklavencode:

#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));  
}