i2c_voltage.ard

#include <Wire.h>

#define SLAVE_ADDRESS 0x04

#define LED  6
int number = 0;

// Pin that input voltage and resistors are connected
// doc here resistor setup
int inputPin = A0 ;
// calculation to get voltage from analog reading
double voltageMultiplier = 1023/5/3.10 ;
int val;
double volts;
String voltsPrefix = "Volts: ";
String piOutput;

void setup() {
  Serial.println("Starting setup...");
  Serial.begin(9600);
  // i2c setup
  Wire.begin(SLAVE_ADDRESS);
  Wire.onReceive(receiveData);
  Wire.onRequest(sendData);
  Serial.println("Ready!");
}

void loop() 
{
  val = analogRead(inputPin);
  Serial.print("Analog is: ");
  Serial.print(val);
  Serial.print(", volts: ");
  // get volts based on the multiplier from resistor voltage divider 
  volts = val / voltageMultiplier;
  Serial.println(volts);
  piOutput = ("Volts:" + String(volts) + "|RawAnalog:" + val + "|");  
//  char buff[10];
//  sprintf(buff, "00%d", int(volts*100));
//  Serial.print(buff);
  Serial.println(piOutput);

  delay(500);
  voltsPrefix = "";
}

void receiveData(int byteCount) {
  Serial.println("receiveData");
  while (Wire.available()) {
    number = Wire.read();
    Serial.print("data received: ");
    Serial.println(number);
    if (number == 1) {
      Serial.println(" LED ON");
      digitalWrite(LED, HIGH);
    } else {
      Serial.println(" LED OFF");
      digitalWrite(LED, LOW);
    }
  }
}

void sendData() {
//  Wire.write(number);
  Serial.println("Sending to pi..." + piOutput);
  Wire.write(piOutput.c_str());
  delay(500);
 }