This is my first attempt at controlling an LED matrix. I’m using a 5x7 matrix with a SN74LS164N shift register. Code to scroll "HELLO WORLD!!! " is below.
I tried running dispDraw() on interrupts with code shamefacedly copied and pasted, but only the first row would draw. Could this have been because a new interrupt was “triggered” before a draw was finished? (I’m on a 328, BTW)
Mostly, I’d deeply appreciate any general feedback on glaring inefficiencies, things done properly, etc…, because I’m sort of shooting in the dark 
Also, if I’ve broken any etiquettes by the manner in which I’ve posted, or by my request, please do help me lose my ignorance.
Thanks very much in advance!
Datasheets:
(http://www.datasheetcatalog.org/datasheets2/15/157524_1.pdf)
(http://www.datasheetcatalog.org/datasheet2/8/0upt0oxpqizjodhogqshk59g1ucy.pdf)
int row[5] = { //PINS USED FOR EACH ROW
2, 3, 4, 5, 6};
int dataPin = 7;
int clockPin = 8;
int blankPin = 9; //UNUSED
int letter[][15] = { //3X5 FONT, DEFINED FROM UPPER LEFT CORNER, MOVING ROW BY ROW
{
0,1,0,1,0,1,1,1,1,1,0,1,1,0,1 } //A
,{
1,1,0,1,0,1,1,1,1,1,0,1,1,1,0 } //B
,{
0,1,0,1,0,1,1,0,0,1,0,1,0,1,0 } //C
,{
1,1,0,1,0,1,1,0,1,1,0,1,1,1,0 } //D
,{
1,1,1,1,0,0,1,1,0,1,0,0,1,1,1 } //E
,{
1,1,1,1,0,0,1,1,0,1,0,0,1,0,0 } //F
,{
0,1,1,1,0,0,1,0,1,1,0,1,0,1,1 } //G
,{
1,0,1,1,0,1,1,1,1,1,0,1,1,0,1 } //H
,{
1,1,1,0,1,0,0,1,0,0,1,0,1,1,1 } //I
,{
0,1,1,0,0,1,0,0,1,1,0,1,0,1,0 } //J
,{
1,0,1,1,0,1,1,1,0,1,0,1,1,0,1 } //K
,{
1,0,0,1,0,0,1,0,0,1,0,0,1,1,1 } //L
,{
1,0,1,1,1,1,1,1,1,1,0,1,1,0,1 } //M
,{
1,1,1,1,0,1,1,0,1,1,0,1,1,0,1 } //N
,{
0,1,0,1,0,1,1,0,1,1,0,1,0,1,0 } //O
,{
1,1,0,1,0,1,1,1,0,1,0,0,1,0,0 } //P
,{
0,1,0,1,0,1,1,0,1,0,1,1,0,0,1 } //Q
,{
1,1,0,1,0,1,1,1,0,1,0,1,1,0,1 } //R
,{
0,1,1,1,0,0,0,1,0,0,0,1,1,1,0 } //S
,{
1,1,1,0,1,0,0,1,0,0,1,0,0,1,0 } //T
,{
1,0,1,1,0,1,1,0,1,1,0,1,1,1,1 } //U
,{
1,0,1,1,0,1,1,0,1,1,0,1,0,1,0 } //V
,{
1,0,1,1,0,1,1,1,1,1,1,1,1,0,1 } //W
,{
1,0,1,1,0,1,0,1,0,1,0,1,1,0,1 } //X
,{
1,0,1,1,0,1,0,1,0,0,1,0,0,1,0 } //Y
,{
1,1,1,0,0,1,0,1,0,1,0,0,1,1,1 } //Z
,{
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 } //SPACE
,{
0,0,0,0,0,0,0,0,0,0,0,0,1,0,0 } //PERIOD
,{
1,0,0,1,0,0,1,0,0,0,0,0,1,0,0 } //EXCLAMATION POINT
};
int message[] = {
7,4,11,11,14,26,22,14,17,11,3,28,28,28,28,26}; //"HELLO WORLD!!! "
int messageLength = sizeof(message)/sizeof(int);
int messageIndex = 0; //TO TRACK WHICH LETTER IS CURRENTLY BEING DRAWN
int scrollSpeed = 10;
int chunkTick = 0; //WHICH OF THREE COLUMNS OF CURRENT LETTER (OR A SPACING COLUMN) IS BEING DRAWN
int disp[5][7] = { //ARRAY STORES CURRENT DISPLAY, INITIALIZED WITH HATCH TEST PATTERN
{
1,0,1,0,1,0,1 }
,{
0,1,0,1,0,1,0 }
,{
1,0,1,0,1,0,1 }
,{
0,1,0,1,0,1,0 }
,{
1,0,1,0,1,0,1 }
};
void setup() {
for (int i = 0; i < 5; i++) {
pinMode(row[i], OUTPUT);
digitalWrite(row[i], HIGH);
}
pinMode(dataPin, OUTPUT);
digitalWrite(dataPin, LOW);
pinMode(clockPin, OUTPUT);
digitalWrite(clockPin, LOW);
pinMode(blankPin, OUTPUT);
digitalWrite(blankPin, HIGH);
}
void loop() {
for (int i = 0; i < scrollSpeed; i++) { //THIS IS IN LIEU OF GETTING INTERRUPTS TO WORK. LOOKS FINE ON A SINGE 5X7 MATRIX
drawDisp();
}
switch (chunkTick) { //CHECKS TO SEE WHICH COLUMN OF LETTER NEEDS TO BE ADDED TO DISPLAY
case 0:
{
shiftDisp(); //MOVES DATA IN ARRAY "LEFT" ONE COLUMN
for (int i = 0; i < 5; i++) { //chunkTick IS 1, THEREFORE WRITE THE FIRST COLUMN OF A NEW LETTER TO THE FAR-RIGHT COLUMN OF DISP
disp[i][6] = letter[message[messageIndex]][3*i];
}
chunkTick++;
break;
}
case 1:
{
shiftDisp();
for (int i = 0; i < 5; i++) { //WRITE SECOND COLUMN OF A LETTER
disp[i][6] = letter[message[messageIndex]][3*i + 1];
}
chunkTick++;
break;
}
case 2:
{
shiftDisp();
for (int i = 0; i < 5; i++) { //THIRD COLUMN
disp[i][6] = letter[message[messageIndex]][3*i + 2];
}
chunkTick++;
messageIndex++; //INDICATE LETTER IS COMPLETE, MOVE TO NEXT
if (messageIndex >= messageLength) { //RESTART MESSAGE IF COMPLETE
messageIndex = 0;
}
break;
}
case 3:
{
shiftDisp();
for (int i = 0; i < 5; i++) { //BLANK COLOUMN TO SPACE LETTERS
disp[i][6] = 0;
}
chunkTick = 0;
break;
}
}
}
void shiftDisp() { //I KNOW THERE'S GOT TO BE A BETTER WAY TO DO THIS, BUT IF I'M ONLY DOING IT A FEW TIMES A SECOND...?
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 6; j++) {
disp[i][j] = disp[i][j+1];
}
}
}
void drawDisp() { //"OPTIMIZED" FOR WHEN I WAS TRYING TO RUN ON A TIMER INTERRUPT
for (int i = 0; i < 5; i++) {
PORTD ^= (1 << row[i]); //"SELECT" COLUMN BY BRINGING PIN LOW
PORTD |= (1 << dataPin); //WRITE ARBITRARY MSB, B/C MATRIX IS ONLY 7-WIDE
pulseClock();
for (int j = 0; j < 7; j++) {
PORTD &= ~(1 << dataPin); //COLUMN SELECT
PORTD |= (disp[i][j] << dataPin); //READ RESPECTIVE BIT FROM DISP[][] ARRAY
pulseClock(); //WRITE TO SHIFT REGISTER
}
delay(1);
PORTD ^= (1 << row[i]); //BRING ROW HIGH TO TURN OFF
}
}
pulseClock() {
PORTB |= (1 << (clockPin-8));
PORTB &= ~(1 << (clockPin-8));
}