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ESP32-S3 · Keypad

ESP32-S3 Keypad Simulator: Wiring, Code and a Live Circuit

This is a 4x4 membrane keypad wired to an ESP32-S3 DevKitC-1 and scanned live with the Keypad library: open it in the editor, press a key, and the serial monitor prints it.

Eight wires and nothing else: the rows go to 4, 5, 6, 7 and the columns to 15, 16, 17, 18.

Run it in the editorRead the code
  • 3.3 V logic
  • Library: Keypad.h
  • 8 pins, no resistors
  • Debounced in the library
ESP32-S3 · Keypadlive0.000 s 0.00x
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The circuit itself, running on the simulator with the sketch below. Press what can be pressed; click anything else to open it in the editor.

Wiring the Keypad to the ESP32-S3

Every connection in the circuit above, with the board’s own pin names.

Keypad pinESP32-S3 pinWhy
R1, R2, R3, R4GPIO 4, GPIO 5, GPIO 6, GPIO 7The rows: the library drives one low at a time.
C1, C2, C3, C4GPIO 15, GPIO 16, GPIO 17, GPIO 18The columns: inputs with pull-ups, read for each row.

A membrane keypad has no power pin: it is sixteen switches at the crossings of four row wires and four column wires. Eight pins of the ESP32-S3 scan it, using the chip’s internal pull-ups, so no resistors are needed.

Pins to leave alone on the ESP32-S3

GPIO 19 and 20 are the USB port’s data lines, GPIO 35 to 37 belong to the PSRAM on octal-PSRAM boards such as the N8R8, and GPIO 0, 3, 45 and 46 are strapping pins.

On a real bench

The DevKitC-1 has two USB sockets: UART for uploading and the serial monitor, USB for the S3’s own USB device. Plug into UART while you work with the Keypad. The board is wide, so a single breadboard leaves only one row free on one side.

The code

The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.

4x4 keypad on ESP32-S3
#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'},
};
byte rowPins[ROWS] = {4, 5, 6, 7};   // R1 to R4
byte colPins[COLS] = {15, 16, 17, 18};   // C1 to C4

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  Serial.begin(115200);
  Serial.println("Press a key");
}

void loop() {
  char key = keypad.getKey();   // 0 when nothing new was pressed
  if (key) {
    Serial.print("Key: ");
    Serial.println(key);
  }
}

makeKeymap(keys) tells the library which character sits at each crossing. rowPins and colPins list the board pins in the order of the keypad’s connector, R1 to R4 and C1 to C4.

getKey() scans the matrix: it pulls each row low in turn and reads the four columns, so a column that reads low is a key held in that row. It returns the key once, when it is first pressed, with a debounce built in, and 0 otherwise.

Serial.begin(115200) opens the serial monitor. Serial is UART0 on the board’s UART socket, at 115200 baud in this sketch.

Common mistakes with the Keypad on the ESP32-S3

Rows and columns swapped

Swap the two arrays and every key prints its mirror across the diagonal, so 2 prints 4. If the wrong keys come out in a pattern, swap rowPins and colPins.

Pins listed in the wrong order

The connector order is R1 to R4 then C1 to C4 on most keypads, left to right with the keys facing you. List the pins in exactly that order or keys move around.

Running out of pins

A 4x4 keypad takes eight pins, which on the ESP32-S3 leaves little room. An I2C port expander such as the PCF8574 scans it over two wires instead.

Questions and answers

Can I simulate a keypad with an ESP32-S3 DevKitC-1?

Yes. The circuit at the top of this page is an ESP32-S3 DevKitC-1 with a 4x4 keypad, running in your browser on a simulated ESP32-S3 (Xtensa LX7). Click a key to press it; the simulated keypad connects that row to that column the way the membrane does. Press Run it in the editor to change the wiring or the code; it is free and needs no account.

Can I detect two keys at once?

Keypad.h has getKeys() for that, and up to about three keys work. More can ghost: a missing key appears to be pressed because of the paths through the others.

How do I make a password lock?

Collect the keys into a string until # is pressed, compare it with the code, and drive a relay or a servo when it matches. The keypad lock project does exactly that.

Does a 4x3 keypad work the same way?

Yes, with COLS set to 3, three column pins and a 4 by 3 keys array. The simulator has a 4x3 keypad part too.

Build your own Keypad project

Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.

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