noob here, stuck

Projects Programming
1

Please help me with these bits of code, I am unable to tell the problems

#include <Wire.h>
#include <math.h>
int sensorpin = A0;

void setup()
{
  pinMode(12, OUTPUT); // sets the LED at pin 12
  double c = 4*(sq(PI));  // declaring the constant 4 pi^2 
  double L = 48;
  Wire.begin(2);      // initializes the i2c bus


}

void loop()
{
  int val = analogRead(sensorpin);
  digitalWrite(12, HIGH);
  if(val > 200)
  {
    do
    {
      double T = 2*(micros()/1000);
    }
    while (val < 200);
  }


  int T2 = (int) T * (int) T; 
  double g = double c* double L/T2;
  delay(25);
  byte Tp = (byte) T2;
  byte gr = (byte) g;
  byte test[2] = {
    Tp, gr  };
  Wire.write(test, 2);
}

and the other

#include <LiquidCrystal.h> // The LCD library
#include <Wire.h> // The i2c bus library

LiquidCrystal lcd(12, 11, 5, 4, 3, 2); //Pins used

void setup()
{
  lcd.begin(16, 2);
  Wire.begin(1);
}


void loop()
{ 
 Wire.requestFrom(2, 96);

 recieveEvent();
 byte thisArray[2];
 lcd.print("The period =");
 lcd.print(thisArray[1]);
 lcd.setCursor(0, 1);  
 lcd.print("The value of g =");
 lcd.print(thisArray[2]);
  

}

void recieveEvent()
{
  while(Wire.available() >0)
  {
    for(int p = 0; p<2; p++)
    {
      byte thisArray[p] = Wire.read();
    }
  }
}

I'm trying to use one uno with an IR light gate that times the period of a pendulum swinging and then sending the info to the other (second bit of code) to display on a 16x2 LCD. Any help?

2

You need to tell us what the problem is, exactly. It's like, "my car is broken".

3

In the first bit of code, these errors come up :

Slave.ino: In function 'void loop()':
Slave:34: error: 'T' was not declared in this scope
Slave:35: error: expected primary-expression before 'double'
Slave:35: error: expected ',' or ';' before 'double'

and in the second

master.ino: In function 'void recieveEvent()':
master:40: error: variable-sized object 'thisArray' may not be initialized

I don't know what to do.

4

You only have to declare a variable once. Preferably at the beginning of your program, unless it's local to a function (which, by the way, is not a bad thing). You already did it with some variables but they are declared inside setup().

Once a variable is declared, like:
int x = 77;

you should reference it without a declarator from that point on, like:

x = 66;

The compiler remembers what data type you asked for.

5

Hi, I just tried that and got

Slave.ino: In function 'void loop()':
Slave:34: error: 'T' was not declared in this scope
Slave:35: error: 'c' was not declared in this scope
Slave:35: error: 'L' was not declared in this scope
6

Tried what? I mean, repost your code.

Declare a variable only once.
Declare it in the function that is used.
Declare it before you use it.
If it is used in multiple functions, declare it outside a function (outside setup() or loop()).

7

Sorry I just fixed the declaration problem;
would you be able to help with this bit of code ?

/*
Ok so, this arduino receives data sent from the other one and
dosen't do anything more than display it. We needed two arduinos
for the number of pins the lcd takes up
*/

#include <LiquidCrystal.h> // The LCD library
#include <Wire.h> // The i2c bus library

LiquidCrystal lcd(12, 11, 5, 4, 3, 2); //Pins used

void setup()
{
  lcd.begin(16, 2);
  Wire.begin(1);
}


void loop()
{ 
 
 Wire.requestFrom(2, 96);

 recieveEvent();
 byte thisArray[2];
 lcd.print("The period =");
 lcd.print(thisArray[1]);
 lcd.setCursor(0, 1);  
 lcd.print("The value of g =");
 lcd.print(thisArray[2]);
  

}

void recieveEvent()
{
  while(Wire.available() >0)
  {
    for(int p = 0; p<2; p++)
    {
      byte thisArray[p] = Wire.read();
    }
  }
}

as it gives this error:

master.ino: In function 'void recieveEvent()':
master:40: error: variable-sized object 'thisArray' may not be initialized
8

Thanks so much, it came up with no errors now, I was just declaring it wrong. Thanks so much