Making a calculator using an Arduino

I have "writter's block". My mind is just "blank" and I have no clue how can I do this

Why don't you just form specific functions for specific tasks like for e.g. >> Add() function for adding and pass on the processed variables(after formulating them for unit place etc.) into the respective function after just checking the * for Add or equal button .

I think one reason you have a bug is that there is just too much going on in the one function. As Nis$hant inferred you should compartmentalise things.

Also I don't think you need all the array shuffling and IMO read_keypad() should return a human-readable value, ie 0-9 and + etc.

For example here's is a simpler way (I think)

long num1;
long num2;
long result;
long *curr_num = num1;
byte key;

loop () {
	key = read_keypad();	// this should return an int == to the numeric key entered or obvious values for '=' etc

	switch (key) {

		case '+':
		    if (curr_num == num1) {	// if first number just start accululating into second number
				curr_num = num2;
			} else {
				addNumbers();		// if the second number add them
			}
			break;
		
		case '=':
			addNumbers();
			break;
				
		default:
			accumulateNumber();
			display_number(curr_num);

	}
}

void addNumbers () {
	result = num1 + num2;
	display_number(result);
	curr_num = num1;
	num1 = 0;
	num2 = 0;
}

void accumulateNumber () {
	*curr_num *= 10;
	*curr_num += key;
}

void display_number(long * num){
	for (int x = 0; x < 8, x++) {
		shiftNum (num % 10);	// send digit out
		num /= 10;
	}
}

This is little more than psuedo code and there's no error checking etc but I think it's easy to follow and if there's a bug it should be easy to isolate.


Rob

Yes Sir ROB i used to do similar coding while i programmed addition/subtraction/division/multiplication calculator back 2 years from now in VB.
The approach is pretty simple and easy to grasp while Mr. Serje may not have any fault in his programme but due to increased cluttering he might not be able to stay on the correct logical path.

@Graynomad

Thanks for your idea. I may change my code if I have issues. Oh yes... I still do... will change the code later.

@NI$HANT

I agree with you. I may have to change my code for a modular method of coding. I have to many if()'s. I will have to do that later.

Updated :

I did re-code the add section, no modular method yet. Still have an issues with the keypad. I have : Double entry and wrong entry. All intermittents problems. I may have to re-design the keypad circuit. Right now, it is not reliable.

As for the code, after the Add section change, still some bugs... But I like the new methode of adding. Just like :

Carry : 1111
1234 <-- Array call : digit_number[]

  • 9876 <-- Array call : add_number[]

Last Digit ->11110 The last digit is the OverFlow. So I add two array + the carry. That is the logic behind the Add routine.

The section that work : entry routine, the clear routine, keypad routine, convert routine and the display routine.
I will use the Serial Monitor to see what is going on.

The updated code is the next post.

Thank for the idea. I will apreaciated that you guys check my code.

Here my updated code :

/*
   size : 2648 bytes
   
   Calculator Version 1.5
   
   Just add a number enter by the keypad and display it.
   With 2 function : Add / Equal ===> * button 
                     Clear ==>  # button
   It will use a MAX7219 for display the data ( for the shiftOut() ).
   and a 4021 for the keypad input data with the use of 
   an NOT gate 74HC14. ( for the shiftin() )
   See the keypad example in the tread for details.
  
   The interrupt use a 72LS20 from the row pins, any LOW signal will
   produce a HIGH pulse to be use has an interrupt signal.

   By Serge J Desjardins
   aka techone / tech37
   Toronto, Ontario, Canada

   Compile and Tested.   
*/

// Keypad Serial pins
const byte latchkeypin = 10;
const byte datakeypin = 12;
const byte clockkeypin = 11;

// Display Serial pins
const byte datadisplaypin = 9;
const byte clockdisplaypin = 8;
const byte latchdisplaypin = 7;

// Anykey and interrupt pin
const byte anykeypin = 2;

// MAX7419 init data
word initdata[5] = { 0x0C01, 0x0F00, 0x0A0B, 0x0B07, 0x09FF };

// Fill the Display array with a blank code
word display_data[8] = { 0x0100, 0x020F, 0x030F, 0x040F, 0x050F, 0x060F, 0x070F, 0x080F };  

// The digit array
byte digit_number[8] = {0,0,0,0,0,0,0,0};

// The second array - The total number
byte add_number[9] = {0,0,0,0,0,0,0,0,0};

// Key press keypad flag 
volatile boolean keystate;

// Overflow flag
boolean over_flow;
// add button flag
boolean add_flag;
// Clear button flag
boolean clear_flag;

// The keypad data 
byte keydata;
byte keynumber;

void setup() 
{
  //start serial
  //Serial.begin(9600);

  //define the pins modes
  pinMode(latchkeypin, OUTPUT);
  pinMode(clockkeypin, OUTPUT); 
  pinMode(datakeypin, INPUT);
  pinMode(datadisplaypin, OUTPUT);
  pinMode(clockdisplaypin, OUTPUT);
  pinMode(latchdisplaypin, OUTPUT);
  pinMode(anykeypin, INPUT);
  // setup the interrupt pin
  attachInterrupt(0,anykeypress,RISING);
  
  /* Init the MAX7419 : Normal Mode
                        Normal Operation
                        Setting the Intensity
                        Numbers of Digits being display
                        Set to Decode Mode
  */
 
  for (int i=0;i<5;i++)
  {  
     digitalWrite(latchdisplaypin, LOW);
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, highByte(initdata[i]));
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, lowByte(initdata[i]) );
     digitalWrite(latchdisplaypin, HIGH);
     delay(5);
  }
  // Blank the display
  display_the_numbers();
  // init the flags and the calculation variable
  keystate = 0;  
  add_flag = 1;
  over_flow = 0;
  clear_flag = 1;  
}  

void loop()
{  
  while ( keystate == 0) 
  { 
     // wait for a key press 
  }
  read_keypad();
  convert_the_keypad_data();
  // Enter the numbers routine  
  if ( ( keynumber < 0x0A ) && ( over_flow == 0 ) )
  {  
     if ( ( add_flag == 1) && ( clear_flag = 1 ) )
     {
       for (int i=0;i<8;i++)
       {
         digit_number[i] = 0;      
         display_data[i] = word ( ( i+1 ), 0x0F );
       }      
     }    
     // Enter the key number and move the arrays data.     
     for (int i=7;i>0;i--)
     {
       digit_number[i] = digit_number[i-1];
       display_data[i]=display_data[i-1];
       display_data[i] = word ( (i+1) , lowByte( display_data[i] ) );
     }
     digit_number[0] = keynumber;     
     display_data[0] = word ( 1, keynumber );     
     display_the_numbers();
     add_flag = 0;
     clear_flag = 0;
     keystate = 0;    
  }
  else
  {
    // Check for the "Add / Equal" button
    if ( ( keynumber == 0x0B ) && ( over_flow == 0) )
    {      
      for (int i=0;i<8;i++)
      {
         add_number[i] = add_number[i+1] + add_number[i] + digit_number[i];
         if (add_number[i] > 0x09 )
         {
           add_number[i+1] = 1;
           display_data[i] = word ( ( i + 1 ), ( add_number[i] - 10 )); 
         }
         else 
         {
            display_data[i] = word ( ( i + 1 ) , add_number[i]);
         }        
      }  
      
      // check for over flow
      if ( add_number[8] > 0)
      {      
        over_flow = 1;
        digit_number[0] = 0;        
        display_data[0] = 0x010B;
        for ( int i=1;i<8;i++)
        {
           digit_number[i] = 0;
           display_data[i] = word( (i+1), 0x0F );               
        }      
        keystate = 0;
        over_flow = 1;
        add_flag = 1;      
        display_the_numbers();           
      }
      else 
      {
        keystate = 0;
        over_flow = 0;
        add_flag = 1;
        display_the_numbers();
      }      
    }
    
    // Check for the "Clear" button 
    if ( keynumber == 0x0E )
    {
      digit_number[0] = 0;
      add_number[0] = 0;
      display_data[0] = 0x0100;
      for ( int i=1;i<8;i++)
      {
        digit_number[i] = 0;
        add_number[i] = 0;
        display_data[i] = word( (i+1), 0x0F );               
      }
      add_number[8] = 0;
      keystate = 0;
      over_flow = 0;
      add_flag = 1;
      clear_flag = 1;
      display_the_numbers();     
    }    
  }   
  //For troubleshooting the program using Serial Monitor
 /*  
    Serial.print(keydata, BIN);
    Serial.print("  ");
    Serial.print(keydata, HEX);
    Serial.print("  ");
    Serial.print(keynumber, HEX);
    Serial.print("  ");
    Serial.println(keydata, DEC);
    delay(1000);
*/
}

// Read keypad data via a 74HC14 - Inverter from the 4021
void read_keypad()
{
  digitalWrite(latchkeypin,HIGH);
  delayMicroseconds(20);
  digitalWrite(latchkeypin,LOW);
  keydata = shiftIn(datakeypin, clockkeypin,LSBFIRST);  
} 

// Convert the keypad data into BCD
// And a code for *, 0, # button
void convert_the_keypad_data()
{
  byte what_row;
  
  what_row = ( keydata >> 3) & 0x0F;
  switch ( what_row)
  {
    case 1:
           keynumber = ( ( keydata >> 1 ) & 0x03 ) + 1;
           break;
    case 2:
           keynumber = (( keydata >> 1 ) & 0x03 ) + 4;
           break;
    case 4:
           keynumber = (( keydata >> 1 ) & 0x03 ) + 7;
           break;
    case 8:
           special_key();
           break;    
  }  
  
}  

// the display the data routine to the MAX7219 
void display_the_numbers()
{
   for (int i=0;i<8;i++)
   {
     digitalWrite(latchdisplaypin, LOW);
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, highByte(display_data[i]) );
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, lowByte(display_data[i]) );
     digitalWrite(latchdisplaypin, HIGH);
     delay(5);
   }  
}

// A special code for 0, *, # button
void special_key()
{
   byte special_case;
   
   special_case = ( ( keydata >> 1) & 0x03 ) + 1;
   switch ( special_case )
   {
     case 1:
            keynumber = 0x0E;
            break;
     case 2:
            keynumber = 0x00;
            break;
     case 3:
            keynumber = 0x0B;
            break;
   }        
}

// Interrupt Routibe
void anykeypress()
{
  keystate = 1; 
}

Updated :

I did place the sections into a routine way. I re-modify my code. Almost the same code, except a bit more "modular"

Issue : The Add section still give me some problems. Sometime, it work, and then it is not, I even see the Over Flow ==> E the Numbers are lock and the add button is lock <== That is expected, that mean it did go through the Add Section. The clear work just great. Still have double entry, and I got the feeling my keypad circuit need to be change. The cause is : When I press a key, the voltage level is not approaching a LOW level for the input of the 74HC14. It is in the "If Zone" <-- "Can Not Make Up It Mind Level". So I will re-design the keypad circuit with LM339, and add a 555 circuit in a monostable mode to take care of the interrupt signal <-- possible cause of the "double" entry. The interrupt signal came from a 74LS20. The 555 is the "deboucing" circuit. And also, I may add a latch chip between the 74LS14 ( that is the buffer after the LM339 output ) and the 4021. Maybe the 555 output ? , or another digital out pin to take care of that ? 555 is a more reliable.

As for my code, I will keep it and test it with the new keypad circuit. Well I may change a bit the Add section... I press Add, and it display : 0000012 . That is just cosmetic bug, I will fix that in the Add section. Just replace the 0 before the 1 with 0x0F <-- code for Display Blank to be send at the MAX7219.

I know, it is sound overkill, I need reliability, that is why I overkill in my circuits and code. I am trying to remove Murphay's Law of the equation. Input + Murphay's Law = Garbage Output

Next post is the updated code.

Here the updated code. I will appreaciated that you guys look at it and tell me what you think.

/*
   size : 2734 bytes
   
   Calculator Version 1.5
   
   Just add a number enter by the keypad and display it.
   With 2 function : Add / Equal ===> * button 
                     Clear ==>  # button
   It will use a MAX7219 for display the data ( for the shiftOut() ).
   and a 4021 for the keypad input data with the use of 
   an NOT gate 74HC14. ( for the shiftin() )
   See the keypad example in the tread for details.
  
   The interrupt use a 72LS20 from the row pins, any LOW signal will
   produce a HIGH pulse to be use has an interrupt signal.

   By Serge J Desjardins
   aka techone / tech37
   Toronto, Ontario, Canada

   Compile and Tested. Still Issues. Maybe it it the Keypad circuit. Not so clean   
*/

// Keypad Serial pins
const byte latchkeypin = 10;
const byte datakeypin = 12;
const byte clockkeypin = 11;

// Display Serial pins
const byte datadisplaypin = 9;
const byte clockdisplaypin = 8;
const byte latchdisplaypin = 7;

// Anykey and interrupt pin
const byte anykeypin = 2;

// MAX7419 init data
word initdata[5] = { 0x0C01, 0x0F00, 0x0A0B, 0x0B07, 0x09FF };

// Fill the Display array with a blank code
word display_data[8] = { 0x0100, 0x020F, 0x030F, 0x040F, 0x050F, 0x060F, 0x070F, 0x080F };  

// The digit array
byte digit_number[8] = {0,0,0,0,0,0,0,0};

// The second array - The total number
byte add_number[9] = {0,0,0,0,0,0,0,0,0};

// Key press keypad flag 
volatile boolean keystate;

// Overflow flag
boolean over_flow;
// add button flag
boolean add_flag;
// Clear button flag
boolean clear_flag;

// The keypad data 
byte keydata;
byte keynumber;

// The choice
byte choise;

void setup() 
{
  //start serial
  //Serial.begin(9600);

  //define the pins modes
  pinMode(latchkeypin, OUTPUT);
  pinMode(clockkeypin, OUTPUT); 
  pinMode(datakeypin, INPUT);
  pinMode(datadisplaypin, OUTPUT);
  pinMode(clockdisplaypin, OUTPUT);
  pinMode(latchdisplaypin, OUTPUT);
  pinMode(anykeypin, INPUT);
  // setup the interrupt pin
  attachInterrupt(0,anykeypress,RISING);
  
  /* Init the MAX7419 : Normal Mode
                        Normal Operation
                        Setting the Intensity
                        Numbers of Digits being display
                        Set to Decode Mode
  */
 
  for (int i=0;i<5;i++)
  {  
     digitalWrite(latchdisplaypin, LOW);
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, highByte(initdata[i]));
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, lowByte(initdata[i]) );
     digitalWrite(latchdisplaypin, HIGH);
     delay(5);
  }
  // Blank the display
  display_the_numbers();
  // init the flags and the calculation variable
  keystate = 0;  
  add_flag = 1;
  over_flow = 0;
  clear_flag = 1;  
}  

void loop()
{  
  while ( keystate == 0) 
  { 
     // wait for a key press 
  }
  read_keypad();
  convert_the_keypad_data();
  // The choise 1 = numbers , 2 = add , 3 = clear
  switch (choise)
  {
     case 1 :
             entry_of_numbers();
             break;
     case 2 :
             add_section();
             break;
     case 3 :
             clear_section();
             break;     
  }  
}

// Choise 1
void entry_of_numbers()
{  
  // Enter the numbers routine  
  if ( over_flow == 0 )
  {  
     if ( ( add_flag == 1) && ( clear_flag = 1 ) )
     {
       for (int i=0;i<8;i++)
       {
         digit_number[i] = 0;      
         display_data[i] = word ( ( i+1 ), 0x0F );
       }      
     }    
     // Enter the key number and move the arrays data.     
     for (int i=7;i>0;i--)
     {
       digit_number[i] = digit_number[i-1];
       display_data[i]=display_data[i-1];
       display_data[i] = word ( (i+1) , lowByte( display_data[i] ) );
     }
     digit_number[0] = keynumber;     
     display_data[0] = word ( 1, keynumber );     
     display_the_numbers();
     add_flag = 0;
     clear_flag = 0;
     keystate = 0;    
  }
}
// Choise 2 - the add section
void add_section()
{
    // Check for the "Add / Equal" button
    if ( over_flow == 0 )
    {      
      for (int i=0;i<8;i++)
      {
         add_number[i] = add_number[i+1] + add_number[i] + digit_number[i];
         if ((add_number[i] > 0x09) && (add_number[i] < 0x14) )
         {
           add_number[i+1] = 1;
           display_data[i] = word ( ( i + 1 ), ( add_number[i] - 10 )); 
         }
         else 
         {
            display_data[i] = word ( ( i + 1 ) , add_number[i]);
         }        
      }  
      
      // check for over flow
      if ( add_number[8] != 0)
      {      
        over_flow = 1;
        digit_number[0] = 0;        
        display_data[0] = 0x010B;
        for ( int i=1;i<8;i++)
        {
           digit_number[i] = 0;
           display_data[i] = word( (i+1), 0x0F );               
        }      
        keystate = 0;
        over_flow = 1;
        add_flag = 1;      
        display_the_numbers();           
      }
      else 
      {
        keystate = 0;
        over_flow = 0;
        add_flag = 1;
        display_the_numbers();
      }      
    }
}

// Choise 3 - The clear section
void clear_section()
{
    // Check for the "Clear" button 
      digit_number[0] = 0;
      add_number[0] = 0;
      display_data[0] = 0x0100;
      for ( int i=1;i<8;i++)
      {
        digit_number[i] = 0;
        add_number[i] = 0;
        display_data[i] = word( (i+1), 0x0F );               
      }
      add_number[8] = 0;
      keystate = 0;
      over_flow = 0;
      add_flag = 1;
      clear_flag = 1;
      display_the_numbers();     
      
}   
  //For troubleshooting the program using Serial Monitor
 /*  
    Serial.print(keydata, BIN);
    Serial.print("  ");
    Serial.print(keydata, HEX);
    Serial.print("  ");
    Serial.print(keynumber, HEX);
    Serial.print("  ");
    Serial.println(keydata, DEC);
    delay(1000);
*/

// Read keypad data via a 74HC14 - Inverter from the 4021
void read_keypad()
{
  digitalWrite(latchkeypin,HIGH);
  delayMicroseconds(20);
  digitalWrite(latchkeypin,LOW);
  keydata = shiftIn(datakeypin, clockkeypin,LSBFIRST);  
} 

// Convert the keypad data into BCD
// And a code for *, 0, # button
void convert_the_keypad_data()
{
  byte what_row;
  
  what_row = ( keydata >> 3) & 0x0F;
  switch ( what_row)
  {
    case 1:
           keynumber = ( ( keydata >> 1 ) & 0x03 ) + 1;
           choise = 1;
           break;
    case 2:
           keynumber = (( keydata >> 1 ) & 0x03 ) + 4;
           choise = 1;
           break;
    case 4:
           keynumber = (( keydata >> 1 ) & 0x03 ) + 7;
           choise = 1;
           break;
    case 8:
           special_key();
           break;    
  }  
  
}  

// the display the data routine to the MAX7219 
void display_the_numbers()
{
   for (int i=0;i<8;i++)
   {
     digitalWrite(latchdisplaypin, LOW);
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, highByte(display_data[i]) );
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, lowByte(display_data[i]) );
     digitalWrite(latchdisplaypin, HIGH);
     delay(5);
   }  
}

// A special code for 0, *, # button
void special_key()
{
   byte special_case;
   
   special_case = ( ( keydata >> 1) & 0x03 ) + 1;
   switch ( special_case )
   {
     case 1:
            keynumber = 0x0E;
            choise = 3;
            break;
     case 2:
            keynumber = 0x00;
            choise = 1;
            break;
     case 3:
            keynumber = 0x0B;
            choise = 2;
            break;
   }        
}

// Interrupt Routibe
void anykeypress()
{
  keystate = 1; 
}

Hi Mr.Serje , had a look on the code,

What about the KeyPad , is it working fine with amp now? i recall you had a problem with that! , May be its having debouncing effect?

One thing notice is that there's no debouncing with the keypad reading. That may cause unreliable input.


Rob

I agree with both of you. I may add a debounce, but I wonder how and where to place the tiny delay ? The key data came from the 4021, after a shiftIn() read. And the interrupt signal came from a 4 input NAND gate - 74LS20. So any bouncing by a key, also created a double pulse at the interrupt pin, activate the interrupt request. A 555 in monostable mode will take care of that. I will re-design the keypad circuit and is not done yet. I may add a latch in between the inverters and the 4021. And beside the bouncing problem, the close contact is not a close contact after all, more than intermittent, due to a non - proper LOW level at the input gates. The LM339 comparator will take care of that. I will set the comparator V ref at 2.5 V <-- mid point. Still two state.

I will keep you guys posted.

I happen to have a PS/2 keypad - see picture. I will re-code using the PS/2 library and re-do a circuit to use the PS/2 keypad and using the same 7 segments display. I will do that later. I will keep you posted on that one too. Still keep the same tread anyway.

Hi Mr.Serje i hope things are fine and the code is hopefully getting done ,following i add my suggestions:

also created a double pulse at the interrupt pin, activate the interrupt request.

I think what here can be done is that as the interrupt is being fired by the NAND gate You can set a counter in here to note the number of times the interrupt routine is being fired and put in a debugging statements on the Serial (I debugged my code in the same way when I was working with interrupts that however came from a mechanical part that is a Reed Switch) this way the real culprit can be traced back, if and only if the debouncing may be happening.

also. Mr.Serje you told once that amplifying(if i recall it right from my memory) the keypad buttons may make then susceptible to ultra sensitivity and thus the same can result in debounce.

I have a keypad/LCD screen that I put both debounce code into it for the usual reasons. I also put a millis count so that I could not double enter the same button.

Pseudo code:

Check for button press twice for debounce
          if good button press, use it,
  if a new button press check millis
 if (millis - last button press) ==  long enough time
  record new button press

The downside is you can push a button too quickly and have it ignored depending how you set the "long enough time variable.

@cyclegadget

Thank for you tips. Using the millis - time to check if a double press is being done... OK I think I get you. To impliment in my code, that I will figure this out. It look like it is a good idea. I will impliment something like that.

Let see :Loop 1 : read key Loop 1 ---> I mean : void loop()
measured time

Loop 2 : readkey
measured time
check the time difference
if to small - don't take the key
if big enough - take the key

Something like that. But with a 555 in monostable - output of the 555 going to the interrupt pin will solve the debouncing problem.
And I will do a digitalWrite( latchkeypin, HIGH ) in the interrupt routine to latch the keypad data.

@NI$HANT

To monitor the interrupt routine using Serial Monitor is a good idea.

also. Mr.Serje you told once that amplifying(if i recall it right from my memory) the keypad buttons may make then susceptible to ultra sensitivity and thus the same can result in debounce

I agree. That the 555 in monostable come in. I just set the output of the 555 about .. let say 10 mS to 20 mS. The input can multi pulse for 1 ms to 8 mS until it is stable, and the 555 chip won't even care about it. It is after the 555 finish it's pulse that the 555 chip care. ( the mono stable circuit, that is )

Updated :

The new keypad circuit is still no done. Today, when I was finish my afternoon run, going home, and in the kitchen, I was thinking about my code, and it occur to me that I made a executable bug in the ADD routine. I was installing the carry into the next array box, that may explain some garbage data in my display. No add right , screw up numbers, etc. Instead to place the carry into the add_number[] array, I just simply use a "temp" variable. Use the / and % to isolate the unit number.

Example : temp = add_number / 10; <-- the carry calculation

  • temp = 12 / 10 --> 1 or 8 / 10 --> 0 *
    Extract Unit : add_number = add_number % 10;
    add_number = 12 % 10 --- > 2 or 8 % 10 ---> 8 <-- the unit to be display.
    Add also, I fix the "cosmetic" bug. Was display : 00001234 Now : 1234
    I change the interrupt routine : I just add : digitalWrite(latchkeypin, HIGH); And remove that line from the read_keypad routine.
    *Next post is the new and final code. <-- I think *
    Here the old code :
    *_</em></em> <em><em><em>*if ( over_flow == 0)     {            for (int i=0;i<8;i++)       {         add_number[i] = add_number[i+1] + add_number[i] + digit_number[i];         if (add_number[i] > 0x09 )         {           add_number[i+1] = 1;           display_data[i] = word ( ( i + 1 ), ( add_number[i] - 10 ));         }         else         {             display_data[i] = word ( ( i + 1 ) , add_number[i]);         }              }              // check for over flow       if ( add_number[8] > 0)       {              over_flow = 1;         digit_number[0] = 0;                display_data[0] = 0x010B;         for ( int i=1;i<8;i++)         {           digit_number[i] = 0;           display_data[i] = word( (i+1), 0x0F );                      }              keystate = 0;         over_flow = 1;         add_flag = 1;              display_the_numbers();                }       else       {         keystate = 0;         over_flow = 0;         add_flag = 1;         display_the_numbers();       }          }*</em></em></em> <em><em>_*

The new Add section
*_</em></em> <em><em><em>*// Choise 2 - the add section void add_section() {     byte temp;       if ( over_flow == 0 )     {       // The Add logic        temp = 0; // the carry variable       for (int i=0;i<8;i++)       {         add_number[i] = temp + add_number[i] + digit_number[i];         temp = add_number[i] / 10;         add_number[i] = add_number[i] % 10;         display_data[i] = word ( ( i + 1 ) , add_number[i] );       }              // check for over flow       if ( temp != 0)       {              over_flow = 1;         digit_number[0] = 0;                display_data[0] = 0x010B;         for ( int i=1;i<8;i++)         {           digit_number[i] = 0;           display_data[i] = word( (i+1), 0x0F );                      }              keystate = 0;         over_flow = 1;         add_flag = 1;              display_the_numbers();                }       else       {         /*         For a cleaner display by removing         the zero's on the left side of the number         */         for (int i=7;i>0;i--)         {           if (add_number[i] == 0)           {             display_data[i] = word ( ( i + 1 ) , 0x0F );           }           else           {             break;           }                  }                  keystate = 0;         over_flow = 0;         add_flag = 1;         display_the_numbers();       }          } }*</em></em></em> <em><em>_*

Here is the updated and maybe the final code. It is working nice, except the issue with the keypad - double entry and miss key.

/*
   size : 2794 bytes
   
   Calculator Version 2.0
   
   Just add a number enter by the keypad and display it.
   With 2 function : Add / Equal ===> * button 
                     Clear ==>  # button
   It will use a MAX7219 for display the data ( for the shiftOut() ).
   and a 4021 for the keypad input data with the use of 
   an NOT gate 74HC14. ( for the shiftin() )
   See the keypad example in the tread for details.
  
   The interrupt use a 72LS20 from the row pins, any LOW signal will
   produce a HIGH pulse to be use has an interrupt signal.

   By Serge J Desjardins
   aka techone / tech37
   Toronto, Ontario, Canada

   Compile and Tested.   
*/

// Keypad Serial pins
const byte latchkeypin = 10;
const byte datakeypin = 12;
const byte clockkeypin = 11;

// Display Serial pins
const byte datadisplaypin = 9;
const byte clockdisplaypin = 8;
const byte latchdisplaypin = 7;

// Anykey and interrupt pin
const byte anykeypin = 2;

// MAX7419 init data
word initdata[5] = { 0x0C01, 0x0F00, 0x0A0B, 0x0B07, 0x09FF };

// Fill the Display array with a blank code
word display_data[8] = { 0x0100, 0x020F, 0x030F, 0x040F, 0x050F, 0x060F, 0x070F, 0x080F };  

// The digit array
byte digit_number[8] = {0,0,0,0,0,0,0,0};

// The second array - The total number
byte add_number[8] = {0,0,0,0,0,0,0,0};

// Key press keypad flag 
volatile boolean keystate;

// Overflow flag
boolean over_flow;
// add button flag
boolean add_flag;
// Clear button flag
boolean clear_flag;

// The keypad data 
byte keydata;
byte keynumber;

// The choice
byte choise;

void setup() 
{
  //define the pins modes
  pinMode(latchkeypin, OUTPUT);
  pinMode(clockkeypin, OUTPUT); 
  pinMode(datakeypin, INPUT);
  pinMode(datadisplaypin, OUTPUT);
  pinMode(clockdisplaypin, OUTPUT);
  pinMode(latchdisplaypin, OUTPUT);
  pinMode(anykeypin, INPUT);
  // setup the interrupt pin
  attachInterrupt(0,anykeypress,RISING);
  
  /* Init the MAX7419 : Normal Mode
                        Normal Operation
                        Setting the Intensity
                        Numbers of Digits being display
                        Set to Decode Mode
  */
 
  for (int i=0;i<5;i++)
  {  
     digitalWrite(latchdisplaypin, LOW);
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, highByte(initdata[i]));
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, lowByte(initdata[i]) );
     digitalWrite(latchdisplaypin, HIGH);
     delay(5);
  }
  // Blank the display
  display_the_numbers();
  
  // Set the latch key LOW
  digitalWrite(latchkeypin, LOW);
  // init the flags and the calculation variable
  keystate = 0;  
  add_flag = 1;
  over_flow = 0;
  clear_flag = 1;   
}  

void loop()
{  
  while ( keystate == 0) 
  { 
     // wait for a key press 
  }
  read_keypad();
  convert_the_keypad_data();
  // The choise 1 = numbers , 2 = add , 3 = clear
  switch (choise)
  {
     case 1 :
             entry_of_numbers();
             break;
     case 2 :
             add_section();
             break;
     case 3 :
             clear_section();
             break;     
  }  
}

// Choise 1
void entry_of_numbers()
{  
  // Enter the numbers routine  
  if ( over_flow == 0 )
  {  
     if ( ( add_flag == 1) && ( clear_flag = 1 ) )
     {
       for (int i=0;i<8;i++)
       {
         digit_number[i] = 0;      
         display_data[i] = word ( ( i+1 ), 0x0F );
       }      
     }    
     // Enter the key number and move the arrays data.     
     for (int i=7;i>0;i--)
     {
       digit_number[i] = digit_number[i-1];
       display_data[i]=display_data[i-1];
       display_data[i] = word ( (i+1) , lowByte( display_data[i] ) );
     }
     digit_number[0] = keynumber;     
     display_data[0] = word ( 1, keynumber );     
     display_the_numbers();
     add_flag = 0;
     clear_flag = 0;
     keystate = 0;    
  }
}
// Choise 2 - the add section
void add_section()
{
    byte temp;
  
    if ( over_flow == 0 )
    { 
      // The Add logic   
      temp = 0; // the carry variable 
      for (int i=0;i<8;i++)
      {
         add_number[i] = temp + add_number[i] + digit_number[i];
         temp = add_number[i] / 10;
         add_number[i] = add_number[i] % 10;
         display_data[i] = word ( ( i + 1 ) , add_number[i] );
      }  
      
      // check for over flow
      if ( temp != 0)
      {      
        over_flow = 1;
        digit_number[0] = 0;        
        display_data[0] = 0x010B;
        for ( int i=1;i<8;i++)
        {
           digit_number[i] = 0;
           display_data[i] = word( (i+1), 0x0F );               
        }      
        keystate = 0;
        over_flow = 1;
        add_flag = 1;      
        display_the_numbers();           
      }
      else 
      {
        /*
        For a cleaner display by removing
        the zero's on the left side of the number
        */
        for (int i=7;i>0;i--)
        {
          if (add_number[i] == 0)
          {
            display_data[i] = word ( ( i + 1 ) , 0x0F );
          }
          else 
          {
            break;
          }          
        }          
        keystate = 0;
        over_flow = 0;
        add_flag = 1;
        display_the_numbers();
      }      
    }
}

// Choise 3 - The clear section
void clear_section()
{
    // Check for the "Clear" button 
      digit_number[0] = 0;
      add_number[0] = 0;
      display_data[0] = 0x0100;
      for ( int i=1;i<8;i++)
      {
        digit_number[i] = 0;
        add_number[i] = 0;
        display_data[i] = word( (i+1), 0x0F );               
      }      
      keystate = 0;
      over_flow = 0;
      add_flag = 1;
      clear_flag = 1;
      display_the_numbers();     
      
}   

// Read keypad data via a 74HC14 - Inverter from the 4021
void read_keypad()
{
 
  delayMicroseconds(10);
  digitalWrite(latchkeypin,LOW);
  keydata = shiftIn(datakeypin, clockkeypin,LSBFIRST);  
} 

// Convert the keypad data into BCD
// And a code for *, 0, # button
void convert_the_keypad_data()
{
  byte what_row;
  
  what_row = ( keydata >> 3) & 0x0F;
  switch ( what_row)
  {
    case 1:
           keynumber = ( ( keydata >> 1 ) & 0x03 ) + 1;
           choise = 1;
           break;
    case 2:
           keynumber = (( keydata >> 1 ) & 0x03 ) + 4;
           choise = 1;
           break;
    case 4:
           keynumber = (( keydata >> 1 ) & 0x03 ) + 7;
           choise = 1;
           break;
    case 8:
           special_key();
           break;    
  }  
  
}  

// the display the data routine to the MAX7219 
void display_the_numbers()
{
   for (int i=0;i<8;i++)
   {
     digitalWrite(latchdisplaypin, LOW);
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, highByte(display_data[i]) );
     shiftOut(datadisplaypin, clockdisplaypin, MSBFIRST, lowByte(display_data[i]) );
     digitalWrite(latchdisplaypin, HIGH);
     delay(5);
   }  
}

// A special code for 0, *, # button
void special_key()
{
   byte special_case;
   
   special_case = ( ( keydata >> 1) & 0x03 ) + 1;
   switch ( special_case )
   {
     case 1:
            keynumber = 0x0E;
            choise = 3;
            break;
     case 2:
            keynumber = 0x00;
            choise = 1;
            break;
     case 3:
            keynumber = 0x0B;
            choise = 2;
            break;
   }        
}

// Interrupt Routibe
void anykeypress()
{
  digitalWrite(latchkeypin, HIGH);
  keystate = 1; 
}

double entry and miss key

okay so it seems Mr.Serje that everything now is fine , i think we guys are done and the code is good the problem arising if any is because of that keypad that is getting beyond our control.

Thanks NI$HANT for your support.

because of that keypad that is getting beyond our control.

I will tame that keypad, don't you worry about it :grin:

I will keep you guys update about my progress. The PS/2 keypad will be use for the same idea. But a more complete project by adding the function : Add, Minus, Multiplication and Division.

Mention not! Mr Serje, I'm always here for you, now lets see how things work with ps 2 keyboard.

I want to do something very similar to this, but I want preset buttons (15, 16, 17, 18, 19, 20, 25) and have those numbers be added when each of the 7 buttons would correlate with the addition of each of the numbers listed. Any advice as to how i would go about this coding?