Program To Display Letter A on 8*8 LED Matrix

Projects Programming
1

For The Project I have used 4017IC to control row moment and 74HC595 shift register to control column moment. I am using pin 1 to 8 of 4017 IC to run 8*8 led matrix

My question is that the program i have crafted is it correct. If yes can any one tell me why the 2 leds at the 8th row are dimmer than the 2,3,4,6,7 row which also have two leds on. Shouldn't their intensities be same.

My question is not regarding current sink or the current required to run 8 leds in a single row as i know i can used a array of 2803 transistor or BC547 transistors. Which i can add later i just wanna find the answer to above problem

int reg_clk=3;
int reg_latch=5;
int reg_data=6;
int row_clk=10;
int row_rst=11;
int current_row=8;

byte ba[8]={B10000001,B10111101,B10111101,B10111101,B10000001,B10111101,B10111101,B10111101};

void setup()
{
  Serial.begin(9600);
  pinMode(reg_clk,OUTPUT);
  pinMode(reg_latch,OUTPUT);
  pinMode(reg_data,OUTPUT);
  pinMode(row_clk,OUTPUT);
  pinMode(row_rst,OUTPUT);
  current_row=0;
  digitalWrite(row_rst,HIGH);
  //delay(10);
  digitalWrite(row_rst,LOW);



  //delay(2000);
  //Serial.println(ba[5]);
}

void loop()
{
  if(current_row<8)
  { 
  
    add_data();
    
    
  }
  else
  {
    ++current_row;
    if(current_row==10)
    {
      current_row=0;
    }
     digitalWrite(reg_latch,LOW);     
    digitalWrite(row_clk,HIGH); 
    digitalWrite(row_clk,LOW);
  //delay(1000);  
  }
}

void add_data()
{

    byte temp=ba[current_row];
    //Serial.println(temp);
    
    
    shiftOut(reg_data,reg_clk,LSBFIRST,temp);
    digitalWrite(row_clk,HIGH); 
    digitalWrite(reg_latch,HIGH);
    digitalWrite(reg_latch,LOW);
    digitalWrite(row_clk,LOW);
    
    
    //delay(1000);
       
  current_row++;
}

Markings.jpg

2

I am guessing the 4017IC is sourcing current, and the shift register is sinking it, yes?

Have you, by any chance, read the data sheet for your specific brand of 4017 chip - especially the bit about how much current a pin can source?

3

Yes 4017 is sourcing the current and shift register 595 sinking it and yes i have also read their datasheets.
The 4017 does not provide enough current to lit 8 leds.(At one given time max leds lit in a row = 8

But current source is enough just to lit them with lower intensity. I will later add transistors to provide alternate current source(2083 or BC547)

In 8*8 matrix if you see in row 2,3,4,6,7 two leds are lit. Similar is the case with 8th row two are lit but their intensity is lesser compared to the 2,3,4,6,7 rows. WHY??? That's what i want to know

My logic is to lit specific leds in each row one at a time and do it so fast that the 8 rows appear to lit together producing my "A" character design.

4

Why go from 0 to 9 when your data is only 8 bits wide?

    if(current_row==10)
    {
      current_row=0;
    }

HC595 is also insufficient to sink current. Look at TPIC6B595 instead.

5

The current_row variable helps to move from one row in the 8*8 matrix to the another. Since 4017 has 10 cycles to clock and i need only 8 (Pin 1 to 9) i need to increment current_row two times while clocking the 4017 IC and doing nothing.

Current_row variable helps to pick the 8 bits data from ba array and latch it onto the 595 IC which sinks the respective column. Whereas the 4017 IC on each cycle makes each row of 8*8 high one at a time.

6

thugsatbay:
Whereas the 4017 IC on each cycle makes each row of 8*8 high one at a time.

... with a maximum of (to quote the first data sheet I find) ...

Source or sink current per output pin, I O (V O > ?0.5 V or V O < V CC + 0.5 V) . . . . . . . . . . . . . . . . . . . . ±25 mA

So, 25mA shared between 2 LEDs is about 12.5mA each. Shared between 8 LEDs is a mere 3.125mA each. Of course, unless you have resistors on each sink that curent source limit is all that is standing between you and a blown LED array.

You need a much higher current source, and ideally a constant current sink. Personally I use an N/P-channel MOSFET pair (switched by a shift register, 4017, IO pin, whatever) to source the current, then an STP16CP05MTR (constant current LED driver) to sink it.