1x4 membrane keypad (4 keys) with ESP32

Supply 3.3 V Bus GPIO

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
COM	Ground	GND	Common line to GND. On some keypads the common is pin 2: check with a multimeter
K1	Output (the part drives it)	D25	Key 1: to a GPIO with INPUT_PULLUP, reads LOW when pressed
K2	Output (the part drives it)	D26	Key 2
K3	Output (the part drives it)	D27	Key 3
K4	Output (the part drives it)	D32	Key 4

Suggested wiring for the 30-pin ESP32 DevKit, avoiding flash, input-only and strapping pins. BoardPilot checks it for you as you wire.

void setup() {
  Serial.begin(115200);
  pinMode(25, INPUT);  // K1
}

void loop() {
  Serial.println(digitalRead(25));
  delay(100);
}

Arduino reference, pinMode INPUT_PULLUP
Common 1x4 membrane keypad, 5-pin ribbon: one common line and one line per key. Pin order varies

Part data: CC BY 4.0, free to reuse with credit to BoardPilot.