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

Question

Helo,

My final aim is to do an 8x8 keypad, presently I have 4x4 keypad available,so am trying out with that. Am using Arduino Uno R3 compatible. My setup is as in the attached: My problem is how to detect the column that went low on key press as to determined the key. Presently any key on Col 0 returns 240; Col1 returns 232; etc (dont know if that is ok. )Please help.

Am coding with visual studio 2015 cSharp +Visual Micro My code is as follow:

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

int led = 7;

byte mask = 0x80;

byte lastmask = 0x10;

byte incoming=0 ;

byte dataOuttest;

byte dataIntest;

int PinState = 0;

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, LOW);

delayMicroseconds(5);

digitalWrite(LatchOut, LOW);//

shiftOut(DataOut, ClockPin, LSBFIRST, mask);

digitalWrite(LatchOut, HIGH);//

digitalWrite(ClockPin, HIGH);

delay(100);

Serial.println(" ");

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

Serial.print(row);

Serial.print(" ");

Serial.print("Mask: ");

Serial.println(mask);

Serial.println(" ");

delay(100);

//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);

Serial.print("Col: ");

Serial.println(col);

Serial.print("InComing: ");

Serial.println(incoming);

/////if(incoming & mask)/////////////////

///{

/// byte keypress = keys[row][col];

/// Serial.print("KeyPRESS: ");

/// Serial.println(keypress); ////////////// here is my probs, dont know how to return the pressed key with my setup

/// }// end of if

delay(600);

} // end of col

if (mask == lastmask)

mask = 0x80;

else

mask = mask >> 1;

} // 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);

digitalWrite(led, HIGH);

}

void loop()

{

/* add main program code here */

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);

digitalWrite(led, HIGH);

}

void loop()

{

/* add main program code here */

KeyDown();

delay(300);

}

obulorn · Accepted Answer

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;
        
}






























@

shabaz · Answer

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.

shabaz · Answer

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.

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

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