B-6 Loop Function

Next you'll add commands in your app code to turn the LED on and off in a repeating pattern.

Turn On LED

Your app can receive signals from inputs using the digitalRead() or analogRead() methods, depending on whether the values being received will be digital or analog.

Your app can send signals to outputs using the digitalWrite() or analogWrite() methods, depending on whether the values being sent will be digital or analog.

DIGITAL VS. ANALOG: Digital inputs and outputs use binary values (such as: HIGH vs. LOW, etc.). Analog inputs and outputs use a range of values (such as: 0-255, etc.)

The LED can be controlled as a digital output that is either "on" or "off".

You'll need to send an "on" signal to the LED pin. Add this code to your app by inserting it within the loop() function (between the curly braces):

digitalWrite(LED, HIGH);

The digitalWrite() method requires two parameters inside its parentheses (in this order):

1. The I/O pin number, which can be the actual pin number (such as: D7, etc.) or a variable that stores a pin number. In this case, the variable LED is listed (which has a value equal to D7).

2. The signal value, which can be HIGH or LOW. Your Photon uses this value to send an electrical signal through the pin: HIGH is a signal of 3.3 volts which represents "on," while LOW is a signal of 0 volts which represents "off." In this case, the signal was set to HIGH because you want to turn on the LED light.

Add Time Delay

You'll want to leave the LED turned on for a short amount of time before you send the "off" signal.

Because the Photon's app code runs very fast, there will be certain situations where you'll want to insert delays into the code, in order to allow time for certain events to occur. Typically, these delays are intended to give people time to perceive the event and/or respond to the event.

Your app can use the delay() method to insert a time delay. It acts like a timer that makes the app wait before performing the next line of code.

You'll need to add a delay after the LED has been turned on. Add this code to your app by inserting it (as a separate line of code) within the loop() function (after the digitalWrite() statement):

delay(1000);

The delay() method requires one parameter inside its parentheses:

• The time value, which can be an integer number (whole number) or a variable that stores an integer. The value represents the number of milliseconds for the delay (1000 ms = 1 second). In this case, the delay was set to 1000 ms (1 second).

Turn Off LED

Next, you'll send an "off" signal to the LED pin. Add this code to your app by inserting it (as a separate line of code) within the loop() function (after the delay() statement):

digitalWrite(LED, LOW);

You can see that the second parameter in this digitalWrite() statement was set to LOW, which represents "off" for a digital output.

Add Another Delay

When all the code within the loop() function has been performed, the loop() will automatically repeat itself. Since the first line of code in your loop() turns on the LED, you'll want to add another delay to leave the LED turned off for a short amount of time before the loop() repeats itself.

Add this code to your app by inserting it within the loop() function (after the second digitalWrite() statement):

delay(1000);

Now, the code within your loop() function should perform these tasks (in order):

1. Turn On LED light

2. Wait 1 second

3. Turn Off LED light

4. Wait 1 second

5. Repeat

REPEATING LOOP: You don't need to add a command to make the loop() function repeat – it automatically repeats itself after its last line of code has been performed.