I2C between mega &uno , sending a float(time) on a stopwatch

Projects Programming
1

Hello,im doing a stopwatch project regarding runner's training.In my main arduino(master) i want to use an nrf24l01 to get feedback from the runner(heart rate etc.) and i want to use at the same time an sd card module to store data such as time,heart rate,body temp.I know that using both of them at the same time is not feasible or very very difficult so i thought of using the protocol I2C to connect another arduino(slave) to the master one so to have the sd module there implemented to store the data.Now the problem that occurs is that i cannot send the time as it is for example as a float(or double).Is there anyway to achieve sending more bytes or is my whole thinking wrong.

#include <LiquidCrystal.h>
#include <Wire.h>
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

void setup()
{
  lcd.begin(16, 2);
  lcd.clear();
  Wire.begin(); // join i2c bus (address optional for master)
  Serial.begin(9600);
  
  pinMode(8, INPUT);
  digitalWrite(8, HIGH);
  pinMode(9, INPUT);
  digitalWrite(9, HIGH);
  pinMode(10, INPUT);
  digitalWrite(10, HIGH);

}
float i = 0;
double a = millis();
double c ;

void loop()
{
lcd.clear();
lcd.print("press start");
delay(200);
  
 if(digitalRead(8) ==HIGH)
 {

    lcd.clear();
 a = millis();
   while(digitalRead(9) == LOW)
   {
   
     c = millis();
   i = (c - a) / 1000;
   lcd.print(i);
   lcd.setCursor(11,0);
   lcd.print("Sec's");
   lcd.setCursor(0,0);
   Serial.println(c);
   Serial.println(a);
   Serial.println(i);
   Serial.println("......");
   delay(200);
   }
   
   if(digitalRead(9) == HIGH)
   {
     while(digitalRead(8) == LOW)
     {
       lcd.setCursor(0,0);
       lcd.print(i);
       lcd.setCursor(11,0);
       lcd.print("Sec's");
       lcd.setCursor(0,0);
       delay(100);
     
 
     }
Wire.beginTransmission(9); // transmit to device #4
 Wire.write("TIME IS ");        // sends five bytes
 Wire.write( i);              // sends one byte  
 Wire.endTransmission();    // stop transmitting
 

 }

 }
  

}
2

I use a union to send floats via I2C. A union is a way to share memory by 2 data types. Make a union that consists of a float and an array of 4 bytes.

union data
{
  float flt;
  byte bytes[4];  
};

Construct an instance of the union and give the float a value.

data heartRate;
heartRate.flt = 60.4;

Now the float and the 4 bytes share the same 4 memory locations so you can use the
Wire.write(array, array size) function to send the 4 bytes.

Wire.beginTransmission(8); // transmit to device #8
  // send 4 byte array
  Wire.write(heartRate.bytes, 4);   
  Wire.endTransmission();    // stop transmitting

At the other end, declare a union and construct an instance in the same manner as the sender,
Read the 4 bytes into the byte array (reassembles the float) and the float will be in the .flt variable.

3

You could use a cast - take the address of the (let's say) float variable, cast it to (let's also say) a pointer to "char", dereference that pointer, and use that to send a buffer of four bytes.*(char*)&floatVariable

4

well tried to convert the time and send it as two different integers.ALthought the data was sent,the decaseconds are not displayed coorrectly.I wiil surely try your codes.