This years grade 12 Computer Engineering summative challenge asked the students to control an 8 x 8 LED matrix using a 4017 decade counter to "scan" the columns and an Arduino to "sink" the rows. Examine the schematic below and you will see that control of any particular LED in the matrix is a matter of making the 4017 pin high and the Arduino pin low. The 4017 chip counts from one to ten and then resets but setting pin 15 high also causes a reset. Connecting pin 9 to 15 causes the ninth count to reset the 4017 back to 1. Our decade counter ends up counting one to eight. Clock pulses on pin 14 make the 4017 count up. The fastest possible digitalWrite(2, HIGH); digitalWrite(2, LOW) cycle from the Arduino is enough for the 4017 to respond.
The usual logic for LED control is to use the Arduino pins to "source" the LED - to go high or "on". An examination of most Logic and microprocessor circuitry specifications will show that these circuits have a higher capacity to "sink" current. That means you need to connect the LED anode to power and the cathode to the Arduino pin. Making the pin low is the same as ground so a zero on the pin will cause the LED to glow. This is a reversal in our usual logic where one = on and zero = off. In this case we need to keep the Arduino pins high and send them low to turn on the LED.
Parts
Arduino UNO
Breadboard
4017
BL-M07C881 - 8x8 LED matrix
8 x 300 ohm resistors (I used an 8 x 470 ohm DIP)
jumper wires (I cut most to length to keep it neat)
Here are the pin-outs for the LED matrix:
STEP 1: Wiring
Matrix 4017
5 -----------------> 3
6 -----------------> 2
7 -----------------> 4
8 -----------------> 7
13 ---------------> 6
14 ---------------> 5
15 ---------------> 1
16 ---------------> 10
Matrix Arduino via a current limiting resistor.
1 -----------------> 6
2 -----------------> 7
3 -----------------> 8
4 -----------------> 9
12 ---------------> 10
11 ---------------> 11
10 ---------------> 12
9 -----------------> 13
Don't forget to wire Arduino pin 2 to 4017 pin 14 for a clk input and pin 3 on the Arduino to to pin 6 on the 4017 to detect a count of 8. Wire 5V from the Arduino to pin 16 on the 4017 and tie the ground to 4017 pins 8 and 13.
Step 2 Testing
Use Blink but change the output pin to 2. Disconnect the wires going to the Arduino pins 6 to 13 . Blink will pulse the 4017 slowly. Connect any one of the 8 disconnected leads to ground. The LEDs on that row should light up one after another. If you reduce the delay the LEDs will light quicker and quicker. A very short delay will make it seem as though the entire row is lit. POV or Persistence of Vision makes it seem as though all 8 LEDs are on at the same time when really only one is on at any given time. You will use this later to minimize the current draw on your circuit.
/*
Blink
Turns on an LED on for one second, then off for one second, repeatedly.
This example code is in the public domain.
*/ // Pin 2 is our 4017 clock.int clk = 2;// the setup routine runs once when you press reset:void setup() { // initialize the digital pin as an output. pinMode(clk, OUTPUT); }// the loop routine runs over and over again forever:void loop() { digitalWrite(clk, HIGH); // turn the LED on (HIGH is the voltage level) delay(1000); // wait for a second digitalWrite(clk, LOW); // turn the LED off by making the voltage LOW delay(1000); // wait for a second}
Step 3 Programming
In the checkmark example below I used an array to 'map' which LEDs I wanted to come on.
/*
Test 4
Test 4 Checkmark
*/
int del = 0; // clk width
int chk = 0; // check for reset signal
int row = 1; // row
int ct = 0; //array counter
int pattern[] = {0,0,0,0,0,0,0,1,
0,0,0,0,0,0,1,0,
0,0,0,0,0,1,0,0,
1,0,0,0,1,0,0,0,
0,1,0,1,0,0,0,0,
0,0,1,0,0,0,0,0,
0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0};
int sensorPin = 3;
void setup() {
Serial.begin(9600);
Serial.println("Start");
// initialize the digital pins as an output.
pinMode(2, OUTPUT); //clk out
pinMode(3, INPUT); // reset sense
for (int i = 6; i <=13; i++){
pinMode(i, OUTPUT);
}
for (row = 6; row <=13; row++){
digitalWrite(row, HIGH);
}
reset();
} // setup
void loop() {
for (row = 6; row<=13; row++){
for(int i=1; i<=8; i++){
if(pattern[ct]==1){
digitalWrite(row, 0);
pulse();
delay(2);
digitalWrite(row, 1);
}
else{
pulse();
}
ct++;
}
}
ct=0;
}
void pulse(){
digitalWrite(2, HIGH);
delay(del);
digitalWrite(2, LOW);
delay(del);
// 8 pulses for 8 rows
}
void reset (){
for (int i = 1; i<=9; i++){
pulse();
Serial.println(i);
chk = digitalRead(sensorPin);
Serial.println(chk);
if (chk==1){
return;
} // if
} // for
} // function
If I were to do this again I would reverse the zeros and ones in pattern[] and then instead of using an if statement to check for a 1 I could have simply written the contents of the array out.
for(int i=1; i<=8; i++){
digitalWrite(row, pattern(ct));
pulse();
delay(2);
digitalWrite(row, 1);
}
ct++;
etc.
Another interesting experiment would be using
Arduino Port D (pins 0 to 7) to control all 8 rows with one command. I usually avoid using pins 0 and 1 but in this case it seems sensible to use them.
Step 4 Challenge
The challenge that earned top marks was to make a set of initials scroll across the matrix. In the example below I used a 2 dimensional array to 'map' the LEDs in a way that would make shifting them easier.
/*
Test 5
Scrolling Checkmark
Implements 2 dimensional array
*/
int del = 0; // clk width
int chk = 0; // check for reset signal
int row = 1; // row
int ct = 0; //array counter
int pattern[8][16] = {
{0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1},
{0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0},
{0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0},
{1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0},
{0,1,0,1,0,0,0,0,0,1,0,1,0,0,0,0},
{0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}
};
int ab=0;
int sensorPin = 3;
void setup() {
Serial.begin(9600);
Serial.println("Start");
// initialize the digital pins as an output.
pinMode(2, OUTPUT); //clk out
pinMode(3, INPUT); // reset sense
for (int i = 6; i <=13; i++){
pinMode(i, OUTPUT);
}
for (row = 6; row <=13; row++){
digitalWrite(row, HIGH);
}
reset();
} // setup
void loop() {
for(ct=0; ct<8 animation="" croll="" ct="" p=""> for (int draw = 0; draw<5 down="" draw="" p="" slow=""> for(int row=0; row<8 p="" row=""> for(int col=0; col<8 col="" p=""> if(pattern[row][col+ct]==1){
digitalWrite(row+6, 0);
pulse();
delay(2);
digitalWrite(row+6, 1);
}
else{
pulse();
}
}//col
} //row
}//draw
}// ct
} // main loop
void pulse(){
digitalWrite(2, HIGH);
delay(del);
digitalWrite(2, LOW);
delay(del);
// 8 pulses for 8 rows
}
/* The reset function is called once during setup.
It pulses the 4017 until it detects an output from
pin 6, indicating that the count is at 8 and the next pulse
will be column 1. */
void reset (){
for (int i = 1; i<=9; i++){
pulse();
Serial.println(i);
chk = digitalRead(sensorPin);
Serial.println(chk);
if (chk==1){ // 4017 pin 6 is high
return; // No need to continue
} // if
} // for
} // function
The array is twice as wide as the matrix to allow a frame 'buffer'. There are probably better ways to manipulate the array to do this.
