Help with Scan code for 4x4 Multiplex keypad with 74hc595/74hc165 Shift Register

Hi Obulor,

Assuming the rest of the code is functioning, then in your KeyDown function you should have a line somewhere that says

return(keypress);

That line will make the function complete, and return control back to your function that called it in the first place, i.e. loop() function.

Your loop() function is currently just calling KeyDown, but not making use of any result.

It should declare a variable of some name, e.g. pressed_char, and the put the return value into it:

byte pressed_char;
pressed_char=KeyDown();

To learn such things, this is described in books on C. It is highly recommended to read up on this, or try some online resources on C programming.

C is simple (in principle) that you can learn a lot just by spending a couple of days reading a book.  Functions and return values will be covered in any book on C.

Hi shabaz,

Many thanks for your time. I understand the point you raised, if you look through the code, the area I commented out, should handle that, but for now, the function is displaying it on the screen. The way  it run now is that, it display (or returns) all the keys in the array, one after another even without any keypress. I believe there should be an if condition that will make the condition display (or return) ONLY the pressed key. The IF condition is what I think should solve my problem. Please help.

Hi Obulor,

The line

/////if(incoming & mask)

should not have /// at the beginning, this is commenting it out.

Nor should the subsequent lines have the //.

Anyway that line

if(incoming & mask)

(i.e. without the //) means that you're checking for the signal to be high.

But, your circuit pulls all the columns to logic high by default.

You need the opposite logic, i.e. the row lines to all be high except one, and

then test for low.

To do that, change:

shiftOut(DataOut, ClockPin, LSBFIRST, mask);

to

shiftOut(DataOut, ClockPin, LSBFIRST, mask^255);

and change

if(incoming & mask)

to

if((incoming & mask)==0)

It might work then. I've not examined it in detail due to time availability. But to troubleshoot, closely examine what you're setting on the rows and what you're expecting to read in as a result.

Hi shabaz,

I understand the commenting part, I did that in the post to emphasize the area I suspect the error was coming from .I will try your suggestion out and get back. Thanks again.

Hi shabaz,

Ok, i made the corrections you pointed out, but here is what i don't understand, assuming :

incoming =240 (ie 11110000) and mask = 127(ie 01111111); my understanding of  bitmask  is that:

11110000

and

01111111

equals

01110000 (ie 112) ===> how does this translate or equals zero?

meanwhile from your earlier post i now modified my code; my mask is now in array like so:

byte Mymask[4] = { 0x7f,0xbf,0xdf,0xef };

byte Mymask[4] = { 0x7f,0xbf,0xdf,0xef };

obulorn  wrote:

 

Hi shabaz,

Ok, i made the corrections you pointed out, but here is what i don't understand, assuming :

 

incoming =240 (ie 11110000) and mask = 127(ie 01111111);...

byte Mymask[4] = { 0x7f,0xbf,0xdf,0xef };

Where did you get this from though? It isn't in your code.

You've got mask initially set to 0x80 hex, which is 128 decimal, not 127. And 128 decimal is 1000 0000 binary, not 0111 1111

At no point in your code does it equal 127 either.

So, I had to perform the inversion. There are many ways of achieving the desired outcome of course.

Now if you change the existing code in different ways (e.g. decide to set mask to 0x7f instead of 0x80) then other bits of code would need to change too, because your right-shift operation further down the code

(the line that is "mask = mask >> 1;") is not going to pad the left side of the bits in the mask with '1'. It will pad with zero.

The inversion operation that I did would have correctly handled the situation and did not require setting the mask to 0x7f.

Anyway, it really is up to you how you wish to achieve the result, there are many ways to skin the cat.

Hi shabaz,

Again many thanks. Yes I modified my code, the portions that handle the mask; here is the modified version:

const int kbdRows = 4;
const int kbdCols = 4;

int LatchIn = 3; //165 pin1
int ClockPin = 5; // 595 pin11 & 165 pin2
int DataIn = 2; //165 pin9
int LatchOut = 6; // 595 pin12
int DataOut = 7; //595 pin14



byte Mymask[4] = { 0x7f,0xbf,0xdf,0xef };

byte  incoming=0 ;
byte dataOuttest;
byte dataIntest;

char keys[kbdRows][kbdCols] =
{
    { '1','2','3','4' },
    { '5','6','7','8' },
    { '9','0','A','B' },
    { 'C','D','E','F' }
};


byte KeyDown()
{
    //595 Here
    
    for (int row  = 0; row < kbdRows; row++)
    {
        
                digitalWrite(ClockPin, HIGH);
                delayMicroseconds(5);
                digitalWrite(LatchOut, LOW);//

                shiftOut(DataOut, ClockPin, LSBFIRST, Mymask[row]);
                digitalWrite(LatchOut, HIGH);//
                digitalWrite(ClockPin, LOW);
                
                delayMicroseconds(200);

                Serial.println("  ");
                Serial.print("Row: "); // here was to test for Data Shift Out
                Serial.print(row);

                Serial.print(" ");

                Serial.print("MyMask: "); 
                Serial.println(Mymask[row]);
                Serial.println("  ");
                Serial.println(" ");
                delayMicroseconds(200);

    
    //165 Here
        
                                 
    for (int col = 0; col < kbdCols; col++)

    {
             digitalWrite(ClockPin, LOW);
        
                digitalWrite(LatchIn, LOW);
                delayMicroseconds(5);
                digitalWrite(LatchIn, HIGH);
        
                incoming = shiftIn(DataIn, ClockPin, LSBFIRST);
               digitalWrite(ClockPin, HIGH);
               delay(80);

        Serial.print("Col: ");
        Serial.println(col);
        Serial.print("InComing: ");
        Serial.println(incoming);
        
if((incoming & Mymask[row])==0)
    {
    byte keypress= keys[row][col];
     Serial.print("KeyPRESS: ");
    Serial.println(keypress);

}// end of if
        
        
        delayMicroseconds(200);

    } 

    } // row end

}




void setup()
{

  /* add setup code here */
    pinMode(ClockPin, OUTPUT);
    pinMode(DataOut, OUTPUT);
    pinMode(DataIn, INPUT);
    pinMode(LatchOut, OUTPUT);
    pinMode(LatchIn, OUTPUT);

    digitalWrite(LatchOut, LOW);
    
    digitalWrite(ClockPin, LOW);
    Serial.begin(9600);

}

void loop()
{

  /* add main program code here */

  
  KeyDown();
  delayMicroseconds(200);

}

As a test I attached a led to Row0 /Col0 and when I pressed the corresponding key to Row0/Col0; the led turns up , but the IF condition at line 78 is not display(or returning) the corresponding keypad character (that is my problem). Can you please look at that IF condition again.

Many thanks for your time.

Many thanks shabaz, i was able to sort the issue out. I had to include a saperate Column masking and its working now. The only challange is that its not waiting for keypress. I want  to open a new thread for that. Here is the working code for anyone that may need.

const int kbdRows = 4;
const int kbdCols = 4;
int row, col;
int LatchIn = 3; //165 pin1
int ClockPin = 5; // 595 pin11 & 165 pin2
int DataIn = 2; //165 pin9
int LatchOut = 6; // 595 pin12
int DataOut = 7; //595 pin14

int mask = 0x80;
int lastmask = 0x10;
int ColMask = 0x80;
int lastColMask = 0x10;
char keypress;
char Keycode;
int result = 0;
int incoming = 0;
int RtnIncoming = 0;
char mykeys[kbdRows][kbdCols] =
{
    { '1','2','3','4' },
    { '5','6','7','8' },
    { '9','0','A','B' },
    { 'C','D','E','F' }
};
char ScanCode()
{
    if (incoming & ColMask)
    {

        keypress = mykeys[row][col];
        
        return keypress;
        
    } // end if
}
int ReadInput()
{
    //165 Here
    digitalWrite(ClockPin, HIGH);
    digitalWrite(LatchIn, LOW);
    delayMicroseconds(5);
    digitalWrite(LatchIn, HIGH);
    delayMicroseconds(5);
        incoming = shiftIn(DataIn, ClockPin, LSBFIRST);
        delayMicroseconds(200);

    return incoming;

}
int KeyDown()
{
    
        //595 Here

    for (row = 0; row < kbdRows; row++)
    {
        digitalWrite(LatchOut, LOW);//
        shiftOut(DataOut, ClockPin, LSBFIRST, mask);
        digitalWrite(LatchOut, HIGH);//
     
        delay(50);
        //165 Here

        RtnIncoming = ReadInput();
        
        delayMicroseconds(200);
        ///delay(150);
        

        for (col = 0; col < kbdCols; col++)

        {
            if (RtnIncoming != 0)
            {
                switch (col)
                {
                case 0:

                    ColMask = 0x40;

                    if (RtnIncoming & ColMask)
                    {

                     Keycode=ScanCode();
                    
                    } // end if

                    break;

                case 1:

                    ColMask = 0x20;

                    if (RtnIncoming & ColMask)
                    {
                         Keycode = ScanCode();
                        
                    } // end if
                    break;
                case 2:

                    ColMask = 0x10;

                    if (RtnIncoming & ColMask)
                    {

                     Keycode = ScanCode();
                    
                    } // end if
                    break;
                case 3:

                    ColMask = 0x80;

                    if (RtnIncoming & ColMask)
                    {

                     Keycode = ScanCode();
                    

                    } // end if
                    break;

                //default:
                    
                    
                //    break;


                } // end switch

            } // end not zero


        }    //end col for
    
            if (mask == lastmask)
             {
                 mask = 0x80;

                }
              else
           {
               mask = mask >> 1;
           }
               
  } // row end
  
  return Keycode;
        
}






























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Please any one using this code should pull down  and Not  pull up as in the attached schematics