Week Z

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Multiplexed Displays

from Electronic Technologies for Art

Dot Matrix

Circuit

http://www.best-microcontroller-projects.com/support-files/led-dot-matrix-display.pdf

You will need:

  • 5 x 470 ohm resistors
  • 1 LN2803 (NPN transistor array)
  • 1 4017 (decade counter)

It will use 7 output pins on your controller: 5 for the column data, one as the clock for the counter, and one to reset the clock counter. Thats pretty good.

If you are going to drive two 5x7 arrays, you can use the same clock signal and reset for both decade counters, so you will only need 12 pins total, to draw any picture you want, 10x7 pixels wide. This is pretty cool.

  • Decade counter and single data output. You will see a moving line of lights.
  • Decade counter with 5 lines of output.

Arduino Code

plain multiplexer

draws a solid block of lights

/*
 * Multiplexer
 *
 * Driving a multiplexed 5X7 LED display.
 * 1 clock signal drives a decade counter
 * to select lines 1-7.  1 reset pin.
 * 5 data lines drive columns 1-5.
 */

int clockPin = 8; // CP input (pin 14) on 4017 decade counter. 
int resetPin = 9; // MR (pin 15) on 4017.
                     
void setup()                    // run once, when the sketch starts
{
  pinMode(clockPin, OUTPUT);
  pinMode(resetPin, OUTPUT);
  
  // set row pins to be outputs
  for(int j=0;j<7;j++)
    pinMode(j, OUTPUT);
  
}

void loop()                     
{
  
  for (int col=0; col<5; col++)
  {
    for(int row=0;row<7;row++)
      digitalWrite(row, HIGH);
    delay(1);
  
    // send the next clock pulse
    // (to move the decade counter
    digitalWrite(clockPin, HIGH);   
    digitalWrite(clockPin, LOW);
  };
  
  // reset the counter to the first column
  digitalWrite(resetPin, HIGH);
  digitalWrite(resetPin, LOW);
}


smiley

/*
 * Multiplexer
 *
 * Driving a multiplexed 5X7 LED display.
 * 1 clock signal drives a decade counter
 * to select lines 1-7.  1 reset pin.
 * 5 data lines drive columns 1-5.
 */

int clockPin = 8; // CP input (pin 14) on 4017 decade counter. 
int resetPin = 9; // MR (pin 15) on 4017.

boolean img[5*7] = { 0, 0, 0, 0, 0,
                     0, 1, 0, 1, 0,
                     0, 0, 0, 0, 0,
                     0, 0, 0, 0, 0, 
                     1, 0, 0, 0, 1, 
                     0, 1, 1, 1, 0, 
                     0, 0, 0, 0, 0 };
                     
void setup()                    // run once, when the sketch starts
{
  pinMode(clockPin, OUTPUT);
  pinMode(resetPin, OUTPUT);
  
  // set row pins to be outputs
  for(int j=0;j<7;j++)
    pinMode(j, OUTPUT);
  
}

void loop()                     
{
  
  for (int col=0; col<5; col++)
  {
    for(int row=0;row<7;row++)
      digitalWrite(row, img[col+row*5]);      
    delay(1);
  
    // send the next clock pulse
    // (to move the decade counter
    digitalWrite(clockPin, HIGH);   
    digitalWrite(clockPin, LOW);
  };
  
  // reset the counter to the first column
  digitalWrite(resetPin, HIGH);
  digitalWrite(resetPin, LOW);
}

See Also

Examples -> Library-Matrix