I2C wire.h send 2 variables

Question

I am trying to send 2 variables with wire.h. I tried with this code:

MASTER RECEIVER:

#include <Wire.h> // include la libreria
#include <LiquidCrystal_I2C.h>
#include "RTClib.h"
LiquidCrystal_I2C lcd(0x3E, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
RTC_DS1307 RTC; // orologio
static int anno;
static int giorno;
static int mese;
static int ora;
static int secondo;
static int oldSecondo;
static int minuto;
static int oldMinuto;
static int annoGrezzo;
char t[10] = {};
char v[10] = {};
void setup() {
 Wire.begin(); // join i2c bus with address #4
 lcd.begin(16, 2);
 Serial.begin(9600); // start serial for output
 //-----------orologio-----------
 RTC.begin();
 // Check to see if the RTC is keeping time. If it is, load the time from your computer.
 if (! RTC.isrunning()) {
 Serial.println("RTC is NOT running!");
 // This will reflect the time that your sketch was compiled
 RTC.adjust(DateTime(__DATE__, __TIME__));
 }
 //-----------fine orologio-----------
}
void loop() {
 //------------------------------------------------------------
 // si stampano i dati ricevuti e ricomposti
 //------------------------------------------------------------
 Wire.requestFrom(8, 6);
 int i = 0;
 while (Wire.available()) {
 Serial.println(i);
 t[i] = Wire.read();
 // every character that arrives it put in order in the empty array "t"
 i = i + 1;
 }
 Serial.println(t);
 DateTime now = RTC.now();
 annoGrezzo = now.year();
 anno = (annoGrezzo % 100);
 mese = now.month();
 giorno = now.day();
 ora = now.hour();
 minuto = now.minute();
 lcd.setCursor(0, 0);
 lcd.print(t);
 lcd.setCursor(5,0);
 lcd.print(v);
 lcd.setCursor(0, 1);
 lcd.print(giorno);
 lcd.print(" ");
 lcd.print(mese);
 lcd.print(" ");
 lcd.print(anno);
 lcd.print(" ");
 lcd.print(ora);
 lcd.print(":");
 lcd.print(minuto);
 delay (1000);
 lcd.clear();
}

SLAVE SENDER

#include <Wire.h> // si include la libreria 
//---------------------------------------------------------
char t[10];
char v[10];
void setup() {
 Wire.begin(8);
 // join i2c bus (address optional for master)
 Wire.onRequest(requestEvent);
}
void loop() {
 int mioInt = random(30000);
 int mioInt2 = 1234;
 dtostrf(mioInt, 3, 2, t);
 //convers the float or integer to a string. (floatVar, minStringWidthIncDecimalPoint, numVarsAfterDecimal, empty array); 
 dtostrf(mioInt2, 3, 2, v);
 //------------------------------------------------------
 delay (500);
}
void requestEvent() {
 Wire.write(t);
 Wire.write(v);
}

I'm unable to receive v in my master receiver. Thanks for your help.

• Code Gorilla: I don't have the library to hand, but I think reading requires you to request a certain number of bytes from an I2C address. You don't appear to be doing that. Suggest you look more closely at a working I2C library and see how they do it.
• Mark Smith: You're requesting 6 bytes when you should be requesting 20, if I understand it correctly, and there is no code in the Master to write to v.

Answer 1

I2C is 8-bit data bus, where address can be 7 bit or 10 bit, you can't send more than 8 bit at a time, if you want to send data more than 8 bit you will be sending them like this, for example let you need to send 16 bit data then you send 8 bit LSB first and then 8 bit MSB or vice versa as per your configuration.

Secondly I had noticed you code and noticed many errors, the major one is that you hadn't followed the rules of I2C protocol in your code. I am here attached a link for sample program of arduino i2c slave and master. Go through it you will get your answer.