I got a matrix keypad for a project. I'm trying to write my own keypad code to integrate into my other code. So I downloaded the keypad library from playground and peeked inside.
Here is initialization code for column and row pins. I've never used matrix keypads but the concept doesn't seem so hard. In this particular lib, column pins are pulled HIGH, and row pins are turned into inputs with internal pullup resistor. So when you scan columns, you pull each column pin LOW and read which row is LOW to find out the key pressed. Was the above an appropriate way to access matrix keypads?
What I don't understand about the lib's init code is that they put column init inside a for-loop for row init so the column gets initialized multiple times. No big deal but any reason I don't really know? Can someone provide an answer? Thanks.
void Keypad::initializePins(){
for (byte r=0; r<size.rows; r++){
for (byte c=0; c<size.columns; c++){
pinMode(columnPins[c],OUTPUT);
digitalWrite(columnPins[c],HIGH);
}
//configure row pin modes and states
pinMode(rowPins[r],INPUT);
digitalWrite(rowPins[r],HIGH);
}
}
Sensing code. They pull one column pin LOW and scan all row pins, then pull the column back to HIGH and move on to the next column.
char Keypad::getKey(){
char key = NO_KEY; // Assume that no key is pressed, this is the default return for getKey()
for (byte c=0; c<size.columns; c++){
digitalWrite(columnPins[c],LOW); // Activate the current column.
for (byte r=0; r<size.rows; r++){ // Scan all the rows for a key press.
// The user pressed a button for more then debounceTime microseconds.
if (currentKey == keymap[c+(r*size.columns)]){
// Button hold
if (((millis()-lastUpdate) >= holdTime) && digitalRead(rowPins[r]) == LOW){
transitionTo(HOLD);
}
// Button release
if (((millis()-lastUpdate) >= debounceTime) && digitalRead(rowPins[r]) == HIGH){
transitionTo(RELEASED);
currentKey = NO_KEY;
}
}
// Button pressed event. The user pressed a button.
else if (((millis()-lastUpdate) >= debounceTime) && digitalRead(rowPins[r]) == LOW){
digitalWrite(columnPins[c],HIGH); // De-activate the current column.
key = keymap[c+(r*size.columns)];
lastUpdate = millis();
goto EVALUATE_KEY; // Save resources and do not attempt to parse to keys at a time
}
}
digitalWrite(columnPins[c],HIGH); // De-activate the current column.
}
EVALUATE_KEY:
if (key != NO_KEY && key != currentKey){
currentKey = key;
transitionTo(PRESSED);
return currentKey;
}
else{
return NO_KEY;
}
}
I'll stay on digital matrix pad.