How to use received data with Wire Slave_receiver in void loop

Projects Networking, Protocols, and Devices
1

I am sending distance measurements from the Master Arduino to the Slave using I2C, to control the motors on the Slave.

The Slave Arduino is receiving the data, but I cannot figure out how to use the value in the void loop.

The following code returns the correct value in Serial Monitor, but I suspect the value changes in the void loop.

If I move the Serial.println(x); from the void receiveEvent(int howMany), to the void loop, the value prints as -1 in Serial Monitor.

How do I use the value received from the Master in the void loop?

// buddybotmotors.ino
// -*- mode: C++ -*-

#include <Wire.h>
#include <AccelStepper.h>
#include <MultiStepper.h>

// connect to stepper drivers and the pins they use
// stepper1: step pin = 2 dir pin = 3
// stepper2: step pin = 4 dir pin = 5
AccelStepper stepper1(AccelStepper::DRIVER, 2, 3);
AccelStepper stepper2(AccelStepper::DRIVER, 4, 5);

// initial Motor position values
int pos1 = 0;
int pos2 = 600000000000;

// initial Wire Slave_receiver value
int x = 0; // give a value to the varable to be changed


void setup() {

//stepper setup
   stepper1.setMaxSpeed(9000);
   stepper1.setSpeed(9000);
   stepper1.setAcceleration(1000);
   stepper1.setCurrentPosition(pos1);
   stepper1.moveTo(pos2);

   stepper2.setMaxSpeed(9000);
   stepper2.setSpeed(9000);
   stepper2.setAcceleration(1000);
   stepper2.setCurrentPosition(pos1);
   stepper2.moveTo(pos2);


//Wire Slave_receiver
   Wire.begin(8);                // join i2c bus with address #8
   Wire.onReceive(receiveEvent); // register event
   Serial.begin(9600);           // start serial for output
 
} //end of setup


void loop()
   {     
     


if ((x)> 10)               // If the distance is greater than 10cm, run the motors, else stop the motors
{
 
 if (stepper1.distanceToGo() == 0)
     stepper1.moveTo(-stepper1.currentPosition());
   if (stepper2.distanceToGo() == 0)
     stepper2.moveTo(-stepper2.currentPosition());
   stepper1.run();
   stepper2.run();
   
}
else {

  stepper1.stop();
 stepper2.stop();
 
}
   }

  
 
//Wire Slave_receiver
// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany)
 {
 while (1 < Wire.available())
   { 
   }
 int x = Wire.read();    // receive byte as an integer
 Serial.println(x);         // print the integer
 }
2

Note that the term "void" specifies whether a function, such as loop() or receiveEvent(), returns a value.
Void means no value is returned.

Please read "how to post" and edit your post to include code tags.

3

Thanks for the reply.

I added the code tags to my code.

4

I figured it out.

I coded the Master to only send the distance if it is below 10.
On the Slave, I added a boolean "dist_thresh", and added it to the "receiveEvent" function, and used the boolean to trigger the stop.

// buddybotmotors.ino
// -*- mode: C++ -*-

#include <Wire.h>
#include <AccelStepper.h>
#include <MultiStepper.h>

// connect to stepper drivers and the pins they use
// stepper1: step pin = 2 dir pin = 3
// stepper2: step pin = 4 dir pin = 5
AccelStepper stepper1(AccelStepper::DRIVER, 2, 3);
AccelStepper stepper2(AccelStepper::DRIVER, 4, 5);

// initial Motor position values
int pos1 = 0;
int pos2 = 60000000000000;

// initial Wire Slave_receiver value
int x = 0;



void setup() {

//stepper setup
    stepper1.setMaxSpeed(9000);
    stepper1.setSpeed(9000);
    stepper1.setAcceleration(1000);
    stepper1.setCurrentPosition(pos1);
    stepper1.moveTo(pos2);

    stepper2.setMaxSpeed(9000);
    stepper2.setSpeed(9000);
    stepper2.setAcceleration(1000);
    stepper2.setCurrentPosition(pos1);
    stepper2.moveTo(pos2);


//Wire Slave_receiver
    Wire.begin(8);                // join i2c bus with address #8
    Wire.onReceive(receiveEvent); // register event
    Serial.begin(9600);           // start serial for output

    
  
} //end of setup


bool dist_thresh = false;


void loop()
{
     
 {
 if ( dist_thresh == false ) 
       {
    if (stepper1.distanceToGo() == 0)
      stepper1.moveTo(-stepper1.currentPosition());
    if (stepper2.distanceToGo() == 0)
         stepper2.moveTo(-stepper2.currentPosition());
    stepper1.run();
    stepper2.run(); 
        
       }
 else {

 
    stepper1.stop();
    stepper2.stop(); 
 
          
     }
    
 }
 
}
    

   
  
//Wire Slave_receiver
// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany)
  {
  while (1 < Wire.available())
    { 
    }
  int x = Wire.read();    // receive byte as an integer
  Serial.println(x);         // print the integer
  dist_thresh = true;
  
  }