Oggi ho giocato un pò con il codice per inviare più dati su più datastream di pachube.
Per ogni datastream si possono mandare solo un dato alla volta: non si possono mandare contemporaneamente più dati da rappresentare su un solo grafo o più dati con un unica PUT.
Il modo più semplice per arginare tale problema è usare un algoritmo di scheduling Round Robin: inviare i dati a turno.

Esempio:
*stesso FEED

loop
PUT su DATASTREAM_1 del DATO_X
wait 12secondi
PUT su DATASTREAM_2 del DATO_Y
wait 12secondi

Il risultato è stato questo:

Codice:

/*
  Pachube sensor client
 
 This sketch connects an analog sensor to Pachube (https://www.pachube.com) with one feed
 and two datastreams using a Wiznet Ethernet shield. You can use the Arduino Ethernet shield, or
 the Adafruit Ethernet shield, either one will work, as long as it's got
 a Wiznet Ethernet module on board.
 
 Circuit:
 * Analog sensors attached to analog in 2 and 3
 * Ethernet shield attached to pins 10, 11, 12, 13
 
 This code is in the public domain. 
 
 UPDATE:
 
 *Using Pachube's V2 API
 *Analog sensor attached to analog in 2 and 3 
 *New pachube.com IP
 *Using one feed and two datastreams: first for analog 2 and second for analog 3
 
 08/10/2011
 
 by Andrea Esposito
 www.blackstufflabs.com
 
 */

#include <SPI.h>
#include <Ethernet.h>

// assign a MAC address for the ethernet controller.
// fill in your address here:
byte mac[] = { 
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};
// assign an IP address for the controller:
byte ip[] = { 
  192,168,1,20 };
byte gateway[] = {
  192,168,1,1};	
byte subnet[] = { 
  255, 255, 255, 0 };

//  The address of the server you want to connect to (pachube.com):
byte server[] = { 
  173,203,98,29 }; 

// initialize the library instance:
Client client(server, 80);

long lastConnectionTime = 0;        // last time you connected to the server, in milliseconds
boolean lastConnected = false;      // state of the connection last time through the main loop
const int postingInterval = 12000;  //delay between updates to Pachube.com
short flag=0;

void setup() {
  // start the ethernet connection and serial port:
  Ethernet.begin(mac, ip);
  Serial.begin(9600);
  // give the ethernet module time to boot up:
  delay(1000);
}

void loop() {

  //FEED number on your account settings
  //ex.: String FEED=37040;
  String FEED=YOUR_FEED_HERE;

  //ID_DATASTREAMS setted by you
  //ex.:String ID_STREAMING_1="1";
  String ID_STREAMING_1="YOUR_FIRST_ID_STREAM_HERE";
  String ID_STREAMING_2="YOUR_SECOND_ID_STREAM_HERE";

  // voltage=5v but on my board is 4.91v 
  float voltage=4.91; 

  // read the analog sensor:
  //LM35 on A2
  int sensorCelsius = analogRead(2); 
  sensorCelsius = (voltage * sensorCelsius * 100.0)/1024.0;

  //LM335 on A3
  int sensorKelvin = analogRead(3); 
  sensorKelvin = (voltage * sensorKelvin * 100.0)/1024.0;
  //sensorKelving-=273.15; //if you want it in C°

  // if there's incoming data from the net connection.
  // send it out the serial port. This is for debugging
  // purposes only:
  if (client.available()) {
    char c = client.read();
    Serial.print(c);
  }

  // if there's no net connection, but there was one last time
  // through the loop, then stop the client:
  if (!client.connected() && lastConnected) {
    Serial.println();
    Serial.println("disconnecting.");
    client.stop();
  }

  // if you're not connected, and ten seconds have passed since
  // your last connection, then connect again and send data: 
  if(!client.connected() && (millis() - lastConnectionTime > postingInterval)) 
  { //Round Robin
    if (flag==0) //sending data to first datastream
    {
      sendData(sensorCelsius, FEED, ID_STREAMING_1); 
      flag=1;
      Serial.print("ID_STREAMING_1 = ");
      Serial.println(ID_STREAMING_1);
    }
    else
    { //sending data to second datastream
      sendData(sensorKelvin, FEED, ID_STREAMING_2); 
      flag=0;
      Serial.print("ID_STREAMING_2 = ");
      Serial.println(ID_STREAMING_2);
    }
  }
  // store the state of the connection for next time through
  // the loop:
  lastConnected = client.connected();
}

// this method makes a HTTP connection to the server:
void sendData(int thisData , String myfeed , String myid) {

  //Your API_KEY on your account settings
  String API_KEY="YOUR_API_KEY_HERE"; 

  // if there's a successful connection:
  if (client.connect()) {
    Serial.print("Temperature: ");
    Serial.println(thisData);
    Serial.println("connecting...");

    // send the HTTP PUT request. 
    // fill in your feed address here:
    // PUT /v2/feeds/<feed_id>/datastreams/<datastream_id>
    String myput="PUT /v2/feeds/";
    myput+=myfeed;
    myput+="/datastreams/";
    myput+=myid;
    myput+=" HTTP/1.1n";
    Serial.println(myput);
    client.print(myput);

    client.print("Host: api.pachube.comn");
    // fill in your Pachube API key here:
    client.print("X-PachubeApiKey: ");
    client.print(API_KEY);
    client.print("n");
    client.print("Content-Length: ");

    // calculate the length of the sensor reading in bytes:
    int thisLength = getLength(thisData);
    client.println(thisLength, DEC);

    // last pieces of the HTTP PUT request:
    client.print("Content-Type: text/csvn");
    client.println("Connection: closen");

    // here's the actual content of the PUT request:
    client.println(thisData, DEC);

    // note the time that the connection was made:
    lastConnectionTime = millis();
  } 
  else {
    // if you couldn't make a connection:
    Serial.println("connection failed");
  }
}

// This method calculates the number of digits in the
// sensor reading.  Since each digit of the ASCII decimal
// representation is a byte, the number of digits equals
// the number of bytes:

int getLength(int someValue) {
  // there's at least one byte:
  int digits = 1;
  // continually divide the value by ten, 
  // adding one to the digit count for each
  // time you divide, until you're at 0:
  int dividend = someValue /10;
  while (dividend > 0) {
    dividend = dividend /10;
    digits++;
  }
  // return the number of digits:
  return digits;
}