Signed integers over i2c - new try. Not working.

Using Arduino Project Guidance
1

Hello all.
On transmitter side (I2C slave) i use code

void setup() {
 Wire.begin(2);  
 Serial.begin(9600);Wire.onRequest(requestEvent); 
 }
 void loop() {
 sensorValue = analogRead(analogInPin);  
 outputValue = map(sensorValue, 0, 1023, -100, 100);
 //move to range -100 100
 void requestEvent()
 Serial.println(outputValue);
 {
 // Wire.write(outputValue);
 Wire.write(lowByte(outputValue));
 Wire.write(highByte(outputValue));
 }
 }

on receiver side (i2C master) i use code:

#include <Wire.h>
 #include <LiquidCrystal.h>
 int data = 0;
 LiquidCrystal lcd(10, 4, 5, 6, 7, 8);

 void setup() {
  
 lcd.begin(16, 4);
 lcd.print("OK");

 Wire.begin();  
 Serial.begin(9600);
 }

 void loop() {
 lcd.setCursor(0, 1);
 lcd.print(millis()/1000);


 Wire.requestFrom(2, 2);  
 byte i = 0;
 byte buffer[2] = {0, 0};
 while(Wire.available())  
 {
 buffer[i] =Wire.read();
 i++;
 data = 0;
 data |=buffer[1] & 0xFF;
 data =data << 8;
 data |=buffer[2] & 0xFF;
 }
 Serial.print("Data=");
 Serial.println(data);  
 lcd.setCursor(-4,3);
 lcd.print(data);
 delay(500);
 }

This codes give me wrong data.

Where is error?

Thanks.

2

What are you expecting, and what are you getting instead?

3

CrazyIgels:

 void requestEvent()

Is that your actual code? I would be surprised if that compiled.

4

My code from slave side:

#include <Wire.h>
 
 
const int analogInPin = A0;  
const int led = 9;
int sensorValue = 0;        
int outputValue = 0;        


void setup() 
{                
  Wire.begin(2);              
  Wire.onRequest(requestEvent); 
  pinMode(led, OUTPUT);     
  Serial.begin(9600); 
}


void loop() 
{
   sensorValue = analogRead(analogInPin);            
   outputValue = map(sensorValue, 0, 1023, -100, 100);  
 
 // analogWrite(led, outputValue+100);           
 // print the results to the serial monitor:
  Serial.print("sensor = " );                       
  Serial.print(sensorValue);      
  Serial.print("\t output = ");      
  Serial.println(outputValue);   

  
  digitalWrite(led, LOW);   // turn the LED on (HIGH is the voltage level)
  delay(500);               // wait for a second
  digitalWrite(led, HIGH);    // turn the LED off by making the voltage LOW
  delay(500);               // wait for a second

}

void requestEvent()
{

    Wire.write(highByte(outputValue));
Serial.println(highByte(outputValue));
    Wire.write(lowByte(outputValue));
Serial.println(lowByte(outputValue));
  }

I see in terminal:

sensor = 1023 output = 100
0
100
0
100

Or if i turn pot close to zero:

sensor = 0 output = -100
255
156
255
156

I don,t understand, why i see 4 byte, not two in control section....

I2C Master code is:

#include <Wire.h>
#include <LiquidCrystal.h>
  int data = 0;

  LiquidCrystal lcd(10, 4, 5, 6, 7, 8);

void setup() 
{
  
  lcd.begin(16, 4);
  lcd.print("hello, world!");

  Wire.begin();        
  Serial.begin(9600);
}

void loop() {
  lcd.setCursor(0, 1);
  lcd.print(millis()/1000);

 
Wire.requestFrom(2, 2);    
byte i = 0;
byte buffer[2] = {0, 0};
       while(Wire.available())    
  { 
  i++;
Serial.print("i=");
Serial.println(i);
    buffer[i] =Wire.read();

data = 0;
data |=buffer[1] & 0xFF;
data =data << 8;
data |=buffer[2] & 0xFF;  

Serial.print("Data=");
Serial.println (data);
}


  lcd.setCursor(-4,3);
  lcd.print(data);

  delay(500);
}

I see in terminal:

Data=-25345
i=1
Data=-25345
i=2

But -25345 not equal - 100 !

Whats wrong with my code?

5

That one is easy.

Binary for -25345

1001 1100 1111 1111

Binary for -100

1111 1111 1001 1100
6

In the requestEvent you use two Wire.write and two Serial.println.
The Serial.println may not be used in the requestEvent function.
Combine the data in an array and use a single call to Wire.write.