Push Button

What it is

A 12 mm tactile switch, a 10 kΩ pull-down resistor, and a red LED that lights while the button is down. Released, the pull-down holds SIGNAL at 0 V and your board reads LOW. Pressed, the switch connects SIGNAL to VCC and your board reads HIGH. The front of the board says ACTIVE HIGH, and the back says WORKS ONLY WHILE PRESSED: let go and it is LOW again.

Reading it is one call to digitalRead. Reading it correctly takes one more idea. A mechanical contact does not close once: it bounces, making and breaking a few times in the first milliseconds of a press, and a sketch reading the pin in a fast loop sees every one. A counter wired naively to this button goes up by two or three now and then, which is exactly the kind of bug that looks like bad hardware. The handbook below fixes it in a few lines.

VCC is the voltage your pin sees

The switch joins SIGNAL straight to VCC, so whatever is on VCC is what your pin receives when the button is down:

Never 5V beside a 3.3 V board. With VCC unconnected, the button does nothing and the light never comes on. The LED currents are worked out from a red LED's typical forward voltage, about 2.0 V, rather than measured.

Which pin is which

Button side up, header at the bottom, reading left to right:

The back prints TK04 PUSH BUTTON and WORKS ONLY WHILE PRESSED instead of pin names. Turned over, the square pad is on the right, and it is still GND.

Wiring, in three lines

1. GND to your board's GND.
2. VCC to 5V on an Uno, 3V3 on an ESP32, ESP32-S3 or Pico.
3. SIGNAL to a digital pin: D2 on an Uno, GPIO 25 on an ESP32, GPIO 4 on an ESP32-S3, GP15 on a Pico.

Leave NC unconnected. Set the pin to INPUT, not INPUT_PULLUP: the pull-down is already on the board.

Example

// The GPIO number SIGNAL is wired to.
// Uno: 2. ESP32: 25. ESP32-S3: 4. Pico: 15.
const int BUTTON_PIN = 4;

void setup() {
  Serial.begin(115200);
  pinMode(BUTTON_PIN, INPUT);   // the block has its own pull-down
}

void loop() {
  if (digitalRead(BUTTON_PIN) == HIGH) {   // HIGH is pressed
    Serial.println("pressed");
  } else {
    Serial.println("released");
  }
  delay(200);
}

from machine import Pin
import time

# The GPIO number SIGNAL is wired to. ESP32: 25. ESP32-S3: 4. Pico: 15.
button = Pin(4, Pin.IN)       # no pull: the block has its own

while True:
    if button.value() == 1:   # 1 is pressed
        print("pressed")
    else:
        print("released")
    time.sleep_ms(200)

Where to start

The handbook below is nine short articles, each with a working figure. The first read is the whole build in three wires and a few lines.

If your counter goes up by more than one per press, read why one press counts as several and then debouncing with millis().

And before plugging it into an ESP32, VCC sets the voltage is the one page that protects the board.