Open the editorEditor
Ready-to-teach lab

Arduino button and LED lab: digital input

In this Arduino button and LED lab a sketch reads a push button on pin 2 and lights an LED on pin 13 while it is held, which is the first time a program reacts to the world.

Ages 11 and up, after blink. About 40 minutes. Students read and change an Arduino sketch.

Open this labAssign to my class
The lesson

Objective and parts

By the end, students can

  • Read a digital input with digitalRead.
  • Explain what INPUT_PULLUP does and why a pressed button reads LOW.
  • Turn a reading into a decision, first in one line and then with if and else.

Parts, already on the bench

  • An Arduino Uno
  • One push button, from pin 2 to ground
  • One LED with a 220 ohm resistor on pin 13

Nothing to hand out or collect: the circuit opens built and wired.

Steps

What students do

Each step is short enough to read out. Students work in the simulator beside this page.

Open this lab
  1. Open the lab and press Run. Hold the button down with the mouse: the LED lights while it is held.
  2. Open the code and find the line that reads the button, and the line that sets the LED from it.
  3. Swap HIGH and LOW in the digitalWrite line. Predict what the button does now, then run it.
  4. Put it back. Rewrite that line as an if and an else that do the same job.
  5. Now make the LED blink quickly while the button is held, and stay off otherwise.
  6. Harder: make one press turn the LED on and the next press turn it off.
Questions

Questions for students

Hand these out as they are. The expected answers are under the list, for you.

  1. The button is not pressed. What does digitalRead(2) return, and why?
  2. Why does pressing the button make the pin read LOW?
  3. What would the pin read with plain INPUT and no resistor at all?
  4. For the toggle, why is it not enough to check whether the button is down?
Answer key for the teacher
  1. HIGH. INPUT_PULLUP connects the pin to 5 V through a resistor inside the chip, so an open button reads HIGH.
  2. The button connects the pin straight to ground, which wins over the weak pull-up.
  3. Nothing reliable. The pin would float and pick up noise, reading HIGH or LOW at random.
  4. loop() runs thousands of times during one press. The sketch has to remember the last reading and act only when it changes from up to down.
Go further

For students who finish early

  • Count the presses and print the count to the serial monitor.
  • Add a second button that turns the LED off.
Your class

Give this lab to every student

Assign to my class puts this circuit on each student’s class page as a starter. They change their own copy and hand it in, and the work comes back to you in one list.

The class tools are free for 30 days for one class of up to 20 students, with no card. Opening and running the lab needs no account and stays free.

Assign to my classStart a free class
More labs

The other labs in the set

Ohm's lawCircuits. 40 min.Series and parallelCircuits. 45 min.Voltage dividerCircuits. 40 min.LED and resistorCircuits. 30 min.RC circuitElectronics. 50 min.Transistor switchElectronics. 45 min.Logic gatesElectronics. 40 min.Arduino blinkArduino. 35 min.Traffic lightArduino. 45 min.Ultrasonic distanceArduino. 45 min.Servo sweepArduino. 40 min.All labsThe whole set on one page.