Page 102 - Programming the Photon Getting Started With the Internet of Things

void loop() {

if (digitalRead(D0) == HIGH) {
ledValue = ! ledValue;
digitalWrite(ledpin, ledValue);
}
}

Press the push button a few times and see what happens. You may notice that when you
push the button that the LED may not turn on or off as it should, but when you push it a

few more times, it does turn on or off. As previously explained, this is a perfect example
of how debouncing occurs. Try loading the following sketch with the addition of the
highlighted code in bold:

int ledpin = D0;
int ledValue = LOW;

void setup() {
pinMode (D1, INPUT);
pinMode (ledpin, OUTPUT);
}

void loop() {
if (digitalRead(D1) == HIGH) {

ledValue = ! ledValue;
digitalWrite(ledpin, ledValue);
delay (200);
}
}

Press the push button again a few times—notice anything different? This time it works
fine after inserting a short delay into the program. This is because as soon as the program
registers the first push of the switch, it delays the program before it checks again just in

case there is another bounce on the switch.

Sometimes when writing your code you may need to reverse a value from HIGH to
LOW. You can do this with Boolean logic using the ! or not operator:

ledValue = ! ledValue;

In your program you used this to reverse the value of the LED. You set the LED value as a
global variable at the start, which was LOW, so the equation is “ledValue is equal to not
LOW,” which becomes HIGH. So when we use digitalWrite your value used to light up

the LED is HIGH.