Overview
This tutorial demonstrates how to work with an LED matrix 8×8 display. The display utilizes two analog inputs to accomplish this task.
Sample Code
/*
Row-Column Scanning an 8x8 LED matrix with X-Y input
This example controls an 8x8 LED matrix using two analog inputs
created 27 May 2009
modified 30 Aug 2011
by Tom Igoe
This example works for the Lumex LDM-24488NI Matrix. See
http://sigma.octopart.com/140413/datasheet/Lumex-LDM-24488NI.pdf
for the pin connections
For other LED cathode column matrixes, you should only need to change
the pin numbers in the row[] and column[] arrays
rows are the anodes
cols are the cathodes
---------
Pin numbers:
Matrix:
* Digital pins 2 through 13,
* analog pins 2 through 5 used as digital 16 through 19
Potentiometers:
* center pins are attached to analog pins 0 and 1, respectively
* side pins attached to +5V and ground, respectively.
This example code is in the public domain.
http://www.arduino.cc/en/Tutorial/RowColumnScanning
see also http://www.tigoe.net/pcomp/code/category/arduinowiring/514 for more
*/
// 2-dimensional array of row pin numbers:
const int row[8] = {
2,7,19,5,13,18,12,16 };
// 2-dimensional array of column pin numbers:
const int col[8] = {
6,11,10,3,17,4,8,9 };
// 2-dimensional array of pixels:
int pixels[8][8];
// cursor position:
int x = 5;
int y = 5;
void setup() {
Serial.begin(9600);
// initialize the I/O pins as outputs:
// iterate over the pins:
for (int thisPin = 0; thisPin < 8; thisPin++) {
// initialize the output pins:
pinMode(col[thisPin], OUTPUT);
pinMode(row[thisPin], OUTPUT);
// take the col pins (i.e. the cathodes) high to ensure that
// the LEDS are off:
digitalWrite(col[thisPin], HIGH);
}
// initialize the pixel matrix:
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
pixels[x][y] = HIGH;
}
}
}
void loop() {
// read input:
readSensors();
// draw the screen:
refreshScreen();
}
void readSensors() {
// turn off the last position:
pixels[x][y] = HIGH;
// read the sensors for X and Y values:
x = 7 - map(analogRead(A0), 0, 1023, 0, 7);
y = map(analogRead(A1), 0, 1023, 0, 7);
// set the new pixel position low so that the LED will turn on
// in the next screen refresh:
pixels[x][y] = LOW;
}
void refreshScreen() {
// iterate over the rows (anodes):
for (int thisRow = 0; thisRow < 8; thisRow++) {
// take the row pin (anode) high:
digitalWrite(row[thisRow], HIGH);
// iterate over the cols (cathodes):
for (int thisCol = 0; thisCol < 8; thisCol++) {
// get the state of the current pixel;
int thisPixel = pixels[thisRow][thisCol];
// when the row is HIGH and the col is LOW,
// the LED where they meet turns on:
digitalWrite(col[thisCol], thisPixel);
// turn the pixel off:
if (thisPixel == LOW) {
digitalWrite(col[thisCol], HIGH);
}
}
// take the row pin low to turn off the whole row:
digitalWrite(row[thisRow], LOW);
}
}
The setup() Function
There are three primary things accomplished in the setup() function of this sketch.
1. Serial communication is established at a rate of 9600 baud
2. Pins are initialized to OUTPUT
3. The pixel matrix is initialized by setting each pixel row/column to HIGH
The loop() Function
The loop() function in this sketch performs two main tasks.
1. Read the analog sensors
2. Refresh and draw the screen with the updated readings
Refer to the following sections (i.e. readSensors() and refreshScreen()) for further information.
The readSensors() Function
The readSensors() function reads the analog sensors for the latest readings. These readings will later be used to display information on the display.
The refreshScreen() Function
The refreshScreen() function does just what it says. It refreshes the display connected to the Arduino board. It does this based on the information that is read from the analog sensor(s).
