Arduino/libraries/Firmata/examples/SimpleAnalogFirmata/SimpleAnalogFirmata.pde

/* Supports as many analog inputs and analog PWM outputs as possible.
 *
 * This example code is in the public domain.
 */
#include <Firmata.h>

byte analogPin;

void analogWriteCallback(byte pin, int value)
{
    pinMode(pin,OUTPUT);
    analogWrite(pin, value);
}

void setup()
{
    Firmata.setFirmwareVersion(0, 1);
    Firmata.attach(ANALOG_MESSAGE, analogWriteCallback);
    Firmata.begin(57600);
}

void loop()
{
    while(Firmata.available()) {
        Firmata.processInput();
    }
    for(analogPin = 0; analogPin < TOTAL_ANALOG_PINS; analogPin++) {
        Firmata.sendAnalog(analogPin, analogRead(analogPin)); 
    }
}