The button: let Arduino decide

1Get the parts ready

• the circuit from guide no. 34 (Arduino, breadboard, LED with the 220 Ω resistor)
• a 4-pin pushbutton, the small square kind
• three more jumper wires

2Fit the button and the wires

The button sits across the center channel, like a bridge. Compared with guide no. 34 the ground connection changes: GND goes to the long row at the top marked − (the − rail), and from there two short jumpers bring the minus to the LED and to the button.

Orange wire: pin 13 → resistor (as before). Blue wire: pin 2 → column of the button's left pin. Black wires: GND → − rail; − rail → short leg of the LED; − rail → right pin of the button.

3Write the sketch

// The button: as long as you hold it down the LED stays on and the computer says so.
#include <Arduino.h>

const int LED = 13;          // with the ESP32 write 23
const int BUTTON = 2;        // with the ESP32 write 27

void setup() {
  pinMode(LED, OUTPUT);
  pinMode(BUTTON, INPUT_PULLUP);     // input: at rest it reads HIGH
  Serial.begin(115200);              // opens communication with the computer
  Serial.println("Ready! Press the button");
}

void loop() {
  if (digitalRead(BUTTON) == LOW) {     // LOW = pressed
    digitalWrite(LED, HIGH);
    Serial.println("Pressed");
  } else {                              // otherwise: released
    digitalWrite(LED, LOW);
  }
  delay(200);                           // a short pause
}

4Upload and open the Serial Monitor

Upload as in guide no. 34 (right-pointing arrow). Then open the Serial Monitor: it is the magnifying glass icon at the top right. At the bottom of the monitor, choose the speed 115200, the same as in the sketch.

5Bonus: one press on, one press off

Now the button becomes a switch, like a light switch. You need a variable that remembers whether the LED is on.

// One press switches on, one press switches off: the button becomes a switch.
#include <Arduino.h>

const int LED = 13;          // with the ESP32 write 23
const int BUTTON = 2;        // with the ESP32 write 27
bool ledOn = false;          // remembers whether the LED is on

void setup() {
  pinMode(LED, OUTPUT);
  pinMode(BUTTON, INPUT_PULLUP);
}

void loop() {
  if (digitalRead(BUTTON) == LOW) {            // you pressed it
    ledOn = !ledOn;                            // the exclamation mark flips it: on becomes off and vice versa
    digitalWrite(LED, ledOn ? HIGH : LOW);
    delay(300);                                // pause: one press counts only once
    while (digitalRead(BUTTON) == LOW) {}      // wait until you let go of the button
  }
}

6Challenge yourself

7And with the ESP32?

Same circuit, but: LED on pin 23, button on pin 27, ESP32 GND to the − rail. In the sketch change the two lines: const int LED = 23; and const int BUTTON = 27;. Board to choose: ESP32 Dev Module.