Two LEDs Taking Turns

Part of the First Circuits section of Coddy's Arduino journey. Lesson 5 of 22.

Each LED needs its own pin, its own pinMode() and its own resistor. Here the red LED is on pin 8 and the green one on pin 9.

To make them take turns, turn one on and the other off, wait, then swap:

digitalWrite(8, HIGH);  // red on
digitalWrite(9, LOW);   // green off
delay(1000);

The board runs one line at a time, but very fast: two digitalWrite() lines in a row happen a few millionths of a second apart, so to your eye they change together.

The order of the lines is the order things happen. Read your loop() from top to bottom and say what each LED is doing at every delay().

Challenge

Easy

Make the two LEDs take turns, 500 ms each:

make pins 8 and 9 outputs
red on and green off, wait 500 ms
red off and green on, wait 500 ms

One LED should always be on, never both. Press Run, then Check.

Try it yourself

void setup() {
  // make pins 8 and 9 outputs
}

void loop() {
  // red on, green off, wait

  // red off, green on, wait
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in First Circuits

1Hello, Board

Blink an LED Setup and Loop Change the Blink Speed An LED of Your OwnTwo LEDs Taking TurnsComments in Your Sketch

4Decisions

Decisions with if Choosing with if and else Comparing Values Combining Conditions Read a Button

2Talking to Your Computer

Hello, Serial Monitor Print Versus Println Printing Numbers Your First Variable Counting Up When an Int Runs Out

3Math on the Board

Named Constants Arithmetic Operators Integer Division Decimals with float A Blink That Speeds Up

Practice on your own: Arduino playground