Raspberry Pi Pico Keypad LED Project – Blue LEDs for Numbers, Red LEDs for Letters

🧰

Components Required

🍓

Raspberry Pi Pico

⌨️

4×4 Matrix Keypad (16 keys)

💙

8× Blue LEDs (numbers 1–9)

❤️

4× Red LEDs (letters A–D)

〰️

Resistors (1× per LED, 220Ω)

🔌

Jumper Wires + USB Cable

⚡

How It Works

Number Keys 1–8

Each number key turns on its corresponding blue LED individually.

Key "9" — All Blue ON

Press 9 to light all 8 blue LEDs simultaneously.

Key "0" — Reset Blue

Pressing 0 turns off all blue LEDs at once.

Keys A, B, C, D

Each alphabet key lights up its matching red LED.

Key "*" — All Red ON

Press * to turn on all 4 red LEDs at once.

Key "#" — Reset Red

Pressing # clears all red LEDs simultaneously.

📍

GPIO Pin Mapping

🔵 Blue LEDs (GP2–GP11)

LED1(8)→GP11, LED2(7)→GP10
LED3(6)→GP9,  LED4(5)→GP8
LED5(4)→GP7,  LED6(3)→GP6
LED7(2)→GP5,  LED8(1)→GP4

🔴 Red LEDs (GP2–GP3, GP27–GP28)

LED9(A) →GP3
LED10(B)→GP2
LED11(C)→GP28
LED12(D)→GP27

⌨️ Keypad Rows (GP20–GP26)

R1→GP26, R2→GP22
R3→GP21, R4→GP20

⌨️ Keypad Cols (GP16–GP19)

C1→GP19, C2→GP18
C3→GP17, C4→GP16

📋

Step-by-Step Instructions

Connect the 4×4 Keypad

The keypad has 8 pins — 4 rows and 4 columns. Connect all 8 pins to GPIO pins on the Pi Pico using green jumper wires. Row pins connect to GP26, GP22, GP21, GP20. Column pins connect to GP19, GP18, GP17, GP16. Add pull-down resistors on row lines to prevent floating signals.

Connect the Blue LEDs (Numbers 1–8)

Arrange 8 blue LEDs in a row. Place a 220Ω resistor in series with each LED to limit current. Wire the anodes (+) to GP4 through GP11 on the Pico. These LEDs represent keys 1–8. LED for key 8 connects to GP11, key 7 to GP10, and so on down to key 1 at GP4.

Connect the Red LEDs (A, B, C, D)

Place 4 red LEDs next to the blue row with 220Ω resistors in series. Wire LED-A to GP3, LED-B to GP2, LED-C to GP28, and LED-D to GP27. Connect all cathodes (−) to GND.

Connect Power and Ground

Connect the pull-down resistors for the keypad rows to the 3.3V pin (3V3) on the Pi Pico via a shared rail. Connect all LED cathodes and common grounds to any GND pin on the Pico.

Upload the Code

Copy the Arduino/C++ code below and upload it to your Raspberry Pi Pico using the Arduino IDE with the Pico board package installed. The Keypad.h library handles matrix scanning automatically.

Configure the Reset Keys

The code handles two special reset functions: pressing 0 turns off all 8 blue LEDs, and pressing # turns off all 4 red LEDs. Press 9 to light all blue LEDs, and * to light all red LEDs.

Test and Run

Power the Pico via USB. Press number keys 1–8 to toggle blue LEDs on. Press A–D to toggle red LEDs. Use 0 and # to reset each group. You can also test the full circuit online using the Wokwi simulation link below.

💻

Arduino Code

C++ / Arduino

#include <Keypad.h>

const uint8_t LEDS = 12;
const uint8_t ROWS = 4;
const uint8_t COLS = 4;

char keys[ROWS][COLS] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { '*', '0', '#', 'D' }
};

// Pins for LED1–LED12 (blue: 0–7, red: 8–11)
uint8_t ledPins[LEDS] = { 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 28, 27 };
uint8_t rowPins[ROWS] = { 26, 22, 21, 20 }; // R1–R4
uint8_t colPins[COLS] = { 19, 18, 17, 16 }; // C1–C4

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

void setup() {
  for (uint8_t l = 0; l < LEDS; l++) {
    pinMode(ledPins[l], OUTPUT);
    digitalWrite(ledPins[l], LOW);
  }
}

void loop() {
  char key = keypad.getKey();

  if (key != NO_KEY) {
    switch (key) {
      case '1': digitalWrite(ledPins[0], HIGH); break;
      case '2': digitalWrite(ledPins[1], HIGH); break;
      case '3': digitalWrite(ledPins[2], HIGH); break;
      case '4': digitalWrite(ledPins[3], HIGH); break;
      case '5': digitalWrite(ledPins[4], HIGH); break;
      case '6': digitalWrite(ledPins[5], HIGH); break;
      case '7': digitalWrite(ledPins[6], HIGH); break;
      case '8': digitalWrite(ledPins[7], HIGH); break;
      case '9': // All blue LEDs ON
        for (uint8_t l = 0; l < 8; l++) digitalWrite(ledPins[l], HIGH);
        break;
      case '0': // Reset all blue LEDs
        for (uint8_t l = 0; l < 8; l++) digitalWrite(ledPins[l], LOW);
        break;
      case 'A': digitalWrite(ledPins[8],  HIGH); break;
      case 'B': digitalWrite(ledPins[9],  HIGH); break;
      case 'C': digitalWrite(ledPins[10], HIGH); break;
      case 'D': digitalWrite(ledPins[11], HIGH); break;
      case '*': // All red LEDs ON
        for (uint8_t l = 8; l < 12; l++) digitalWrite(ledPins[l], HIGH);
        break;
      case '#': // Reset all red LEDs
        for (uint8_t l = 8; l < 12; l++) digitalWrite(ledPins[l], LOW);
        break;
    }
  }
  delay(10);
}

🗺️

Wokwi Diagram JSON

How to use: Copy this JSON and paste it into the diagram.json file inside your Wokwi project. It defines all components, their positions, and every wire connection.

diagram.json

{
  "version": 1,
  "author": "Anderson Costa",
  "editor": "wokwi",
  "parts": [
    { "type": "wokwi-pi-pico", "id": "pico", "top": 118, "left": 348, "rotate": 90, "attrs": {} },
    { "type": "wokwi-resistor", "id": "rp1", "top": 349.55, "left": 19.2, "attrs": { "value": "1000" } },
    { "type": "wokwi-resistor", "id": "rp2", "top": 368.75, "left": 19.2, "attrs": { "value": "1000" } },
    { "type": "wokwi-resistor", "id": "rp3", "top": 426.35, "left": 19.2, "attrs": { "value": "1000" } },
    { "type": "wokwi-resistor", "id": "rp4", "top": 397.55, "left": 19.2, "attrs": { "value": "1000" } },
    { "type": "wokwi-membrane-keypad", "id": "keypad1", "top": -30.8, "left": -13.6, "attrs": {} },
    { "type": "wokwi-led", "id": "led1",  "top": 20, "left": 420, "attrs": { "color": "blue", "label": "8" } },
    { "type": "wokwi-resistor", "id": "r1",  "top": 90, "left": 415, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led2",  "top": 20, "left": 400, "attrs": { "color": "blue", "label": "7" } },
    { "type": "wokwi-resistor", "id": "r2",  "top": 90, "left": 395, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led3",  "top": 20, "left": 380, "attrs": { "color": "blue", "label": "6" } },
    { "type": "wokwi-resistor", "id": "r3",  "top": 90, "left": 375, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led4",  "top": 20, "left": 360, "attrs": { "color": "blue", "label": "5" } },
    { "type": "wokwi-resistor", "id": "r4",  "top": 90, "left": 355, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led5",  "top": 20, "left": 340, "attrs": { "color": "blue", "label": "4" } },
    { "type": "wokwi-resistor", "id": "r5",  "top": 90, "left": 335, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led6",  "top": 20, "left": 320, "attrs": { "color": "blue", "label": "3" } },
    { "type": "wokwi-resistor", "id": "r6",  "top": 90, "left": 315, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led7",  "top": 20, "left": 300, "attrs": { "color": "blue", "label": "2" } },
    { "type": "wokwi-resistor", "id": "r7",  "top": 90, "left": 295, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led8",  "top": 20, "left": 280, "attrs": { "color": "blue", "label": "1" } },
    { "type": "wokwi-resistor", "id": "r8",  "top": 90, "left": 275, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led9",  "top": 20, "left": 440, "attrs": { "color": "red",  "label": "A" } },
    { "type": "wokwi-resistor", "id": "r9",  "top": 90, "left": 435, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led10", "top": 20, "left": 460, "attrs": { "color": "red",  "label": "B" } },
    { "type": "wokwi-resistor", "id": "r10", "top": 90, "left": 455, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led11", "top": 20, "left": 480, "attrs": { "color": "red",  "label": "C" } },
    { "type": "wokwi-resistor", "id": "r11", "top": 90, "left": 475, "rotate": 90, "attrs": { "value": "220" } },
    { "type": "wokwi-led", "id": "led12", "top": 20, "left": 500, "attrs": { "color": "red",  "label": "D" } },
    { "type": "wokwi-resistor", "id": "r12", "top": 90, "left": 495, "rotate": 90, "attrs": { "value": "220" } }
  ],
  "connections": [
    [ "pico:GP0", "$serialMonitor:RX", "", [] ],
    [ "pico:GP1", "$serialMonitor:TX", "", [] ],
    [ "keypad1:C4", "pico:GP16", "green", [ "v15", "h132" ] ],
    [ "keypad1:C3", "pico:GP17", "green", [ "v25", "h182" ] ],
    [ "keypad1:C2", "pico:GP18", "green", [ "v35", "h204" ] ],
    [ "keypad1:C1", "pico:GP19", "green", [ "v45", "h222" ] ],
    [ "keypad1:R4", "pico:GP20", "green", [ "v55", "h240" ] ],
    [ "keypad1:R3", "pico:GP21", "green", [ "v65", "h260" ] ],
    [ "keypad1:R2", "pico:GP22", "green", [ "v75", "h286" ] ],
    [ "keypad1:R1", "pico:GP26", "green", [ "v85", "h299" ] ],
    [ "r1:1",  "led1:A",  "green", [ "h0" ] ],
    [ "r2:1",  "led2:A",  "green", [ "h0" ] ],
    [ "r3:1",  "led3:A",  "green", [ "h0" ] ],
    [ "r4:1",  "led4:A",  "green", [ "h0" ] ],
    [ "r5:1",  "led5:A",  "green", [ "h0" ] ],
    [ "r6:1",  "led6:A",  "green", [ "h0" ] ],
    [ "r7:1",  "led7:A",  "green", [ "h0" ] ],
    [ "r8:1",  "led8:A",  "green", [ "h0" ] ],
    [ "r9:1",  "led9:A",  "green", [ "h0" ] ],
    [ "r10:1", "led10:A", "green", [ "h0" ] ],
    [ "r11:1", "led11:A", "green", [ "h0" ] ],
    [ "r12:1", "led12:A", "green", [ "h0" ] ],
    [ "pico:GND.4", "led1:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led2:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led3:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led4:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led5:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led6:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led7:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led8:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led9:C",  "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led10:C", "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led11:C", "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GND.4", "led12:C", "black", [ "v-25", "h-22", "v-77", "h6" ] ],
    [ "pico:GP4",  "r1:2",  "green", [ "v-28", "h10",  "v-20" ] ],
    [ "pico:GP5",  "r2:2",  "green", [ "v-36", "h8"  ] ],
    [ "pico:GP6",  "r3:2",  "green", [ "v-26", "h7"  ] ],
    [ "pico:GP7",  "r4:2",  "green", [ "v-36", "h-3" ] ],
    [ "pico:GP8",  "r5:2",  "green", [ "v-33", "h-13"] ],
    [ "pico:GP9",  "r6:2",  "green", [ "v-23", "h-14", "v-11", "h-10" ] ],
    [ "pico:GP10", "r7:2",  "green", [ "v-22", "h-16", "v-9" ] ],
    [ "pico:GP11", "r8:2",  "green", [ "v-12", "h-17", "v-24", "h-18" ] ],
    [ "pico:GP3",  "r9:2",  "green", [ "v-20", "h10",  "v-20", "h20",  "v-13" ] ],
    [ "pico:GP2",  "r10:2", "green", [ "v-15", "h20",  "v-15", "h20",  "v-22" ] ],
    [ "pico:GP28", "r11:2", "green", [ "v155", "h104" ] ],
    [ "pico:GP27", "r12:2", "green", [ "v165", "h152" ] ],
    [ "rp1:2", "keypad1:R1", "green", [ "h8.4", "v-48" ] ],
    [ "rp2:2", "keypad1:R2", "green", [ "h18",  "v-67.2" ] ],
    [ "rp4:2", "keypad1:R3", "green", [ "h27.6","v-96" ] ],
    [ "rp3:2", "keypad1:R4", "green", [ "h37.2","v-124.8" ] ],
    [ "rp1:1", "rp2:1", "red", [ "v0" ] ],
    [ "rp2:1", "rp4:1", "red", [ "v0" ] ],
    [ "rp4:1", "rp3:1", "red", [ "v0" ] ],
    [ "rp3:1", "pico:3V3", "red", [ "v19.2", "h417.15" ] ]
  ],
  "dependencies": {}
}

🗂️

LED Mapping Summary

Key Pressed	LED Color	Action
1 – 8	Blue	Lights matching blue LED
9	Blue	All 8 blue LEDs ON
0	Blue	Reset — all blue OFF
A, B, C, D	Red	Lights matching red LED
*	Red	All 4 red LEDs ON
#	Red	Reset — all red OFF

🚀

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