Arduino UNO Q - Keypad 4x4
Want to add a full 16-key membrane keypad to your Arduino UNO Q project? In this tutorial, you will learn how to read all 16 keys and build a password entry system — with Telegram alerts too.
In this tutorial, you will learn:
- What a 4x4 keypad is and how it works
- How to wire the 4x4 keypad to Arduino UNO Q
- How to program the MCU (C/C++ Arduino code) to detect key presses
- How to verify a password entered on the keypad
- How to program both the Linux side (Python) and MCU side (C/C++) to read the keypad via Bridge
- How to send Telegram notifications when a key is pressed on Arduino UNO Q
- How to use OpenClaw on Arduino UNO Q with the 4x4 keypad
Hardware Preparation
Or you can buy the following kits:
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables .
Additionally, some of these links are for products from our own brand, DIYables .
Overview of the 4x4 Keypad
A 4x4 keypad has 16 membrane buttons arranged in 4 rows and 4 columns — including digits 0–9, letters A–D, and symbols * and #.
Pinout
A 4x4 keypad has 8 pins, divided into rows and columns:
- 4 pins for rows: R1, R2, R3, R4
- 4 pins for columns: C1, C2, C3, C4
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
| Keypad Pin | Arduino UNO Q MCU |
|---|---|
| R1 (Row 1) | D9 |
| R2 (Row 2) | D8 |
| R3 (Row 3) | D7 |
| R4 (Row 4) | D6 |
| C1 (Col 1) | D5 |
| C2 (Col 2) | D4 |
| C3 (Col 3) | D3 |
| C4 (Col 4) | D2 |
Arduino UNO Q Code
The Arduino UNO Q has two processors working together:
- The STM32 MCU reads the keypad matrix directly using the DIYables_Keypad library
- The Qualcomm MPU runs Debian Linux and handles Wi-Fi, Python, and cloud connectivity
- In this section, only the MCU is programmed — the Linux side stays idle. A later section shows how both processors work together via Bridge.
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
*/
// COPYRIGHT newbiely.com
// AUTHOR: newbiely
// This code is made available for public use without restriction.
// For complete instructions, tutorials, and further information, visit:
// https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
#include <DIYables_Keypad.h>
const int ROW_NUM = 4;
const int COLUMN_NUM = 4;
char keys[ROW_NUM][COLUMN_NUM] = {
{ '1', '2', '3', 'A' },
{ '4', '5', '6', 'B' },
{ '7', '8', '9', 'C' },
{ '*', '0', '#', 'D' }
};
byte pin_rows[ROW_NUM] = { 9, 8, 7, 6 }; // Arduino UNO Q MCU pins for rows
byte pin_column[COLUMN_NUM] = { 5, 4, 3, 2 }; // Arduino UNO Q MCU pins for columns
DIYables_Keypad keypad = DIYables_Keypad(makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM);
void setup() {
Serial.begin(115200);
delay(1500);
Serial.println("Arduino UNO Q Keypad 4x4 ready");
}
void loop() {
char key = keypad.getKey();
if (key) {
Serial.print("Key pressed: ");
Serial.println(key);
}
}
Detailed Instructions
First time with Arduino UNO Q? Follow the Getting Started with Arduino UNO Q tutorial to get your development environment ready before proceeding.
- Connect: Wire the 4x4 keypad to the Arduino UNO Q MCU as shown in the wiring diagram above.
- Open Arduino App Lab: Launch Arduino App Lab and wait until it detects your Arduino UNO Q.
- Create a new App: Click the Create New App button.
- Give the App a name, for example: Keypad4x4
- Click Create to confirm.
- Paste the sketch: Copy the MCU code above and paste it into sketch/sketch.ino. Keep other files as default.
- Install the library: Click the Add sketch library button (the open book icon with a + sign) in the left sidebar.
- Search for DIYables_Keypad created by DIYables.io and click the Install button.
Bricks
No bricks added...
Sketch Libraries
No sketch libra...
Files
python
sketch
.gitignore
README.md
app.yaml
sketch.ino
- Upload: Click the Run button in Arduino App Lab.
- Open the Serial Monitor and press keys on the keypad. You will see each key printed.
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] Arduino UNO Q Keypad 4x4 ready
[2026-04-29 09:00:05] Key pressed: 1
[2026-04-29 09:00:08] Key pressed: A
[2026-04-29 09:00:11] Key pressed: #
Keypad and Password
A common use of a 4x4 keypad is entering a password. Two special keys are used:
- * — clears the current input and starts over
- # — confirms the entry and checks the password
All other keys build up the password string one character at a time.
The logic:
- Press any key → append it to the input buffer
- Press * → clear the input buffer
- Press # → compare input to the stored password, then clear the buffer
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
*/
#include <DIYables_Keypad.h> // DIYables_Keypad library
const int ROW_NUM = 4; //four rows
const int COLUMN_NUM = 3; //three columns
char keys[ROW_NUM][COLUMN_NUM] = {
{'1','2','3'},
{'4','5','6'},
{'7','8','9'},
{'*','0','#'}
};
byte pin_rows[ROW_NUM] = {9, 8, 7, 6}; //connect to the row pinouts of the keypad
byte pin_column[COLUMN_NUM] = {5, 4, 3}; //connect to the column pinouts of the keypad
DIYables_Keypad keypad = DIYables_Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM );
const String password = "1234"; // change your password here
String input_password;
void setup(){
Serial.begin(9600);
Serial.println("Keypad 3x4 password");
input_password.reserve(32); // maximum input characters is 33, change if needed
}
void loop(){
char key = keypad.getKey();
if (key){
Serial.println(key);
if(key == '*') {
input_password = ""; // clear input password
} else if(key == '#') {
if(password == input_password) {
Serial.println("password is correct");
// DO YOUR WORK HERE
} else {
Serial.println("password is incorrect, try again");
}
input_password = ""; // clear input password
} else {
input_password += key; // append new character to input password string
}
}
}
※ NOTE THAT:
Change the password variable to your desired password before uploading. You may use any combination of digits 0–9, letters A–D, and * or # in the password.
Bridge: Linux + MCU
This section shows how to program both processors of the Arduino UNO Q so the Linux side can read keypad presses remotely:
- The 4x4 keypad is connected to the MCU (STM32) — the MCU polls it via keypad.getKey() in loop()
- The MPU cannot read keypad pins directly — it must request the last pressed key from the MCU via Bridge.call()
- The MPU has Wi-Fi — running full Debian Linux, it can react to key presses and send alerts over the Internet
- Arduino_RouterBridge enables RPC communication between the two processors
- ⚠️ /dev/ttyHS1 (Linux) and Serial1 (MCU) are RESERVED by the router — never open them in user code
In short: MCU polls the keypad → MPU reads the last key via Bridge → MPU can react to key presses from anywhere over the Internet.
Note: In the Bridge sketch, keypad.getKey() is called inside the Arduino loop() to continuously detect key presses — this is required and does not interfere with Bridge communication.
MCU Code (Bridge)
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
*/
// COPYRIGHT newbiely.com
// AUTHOR: newbiely
// This code is made available for public use without restriction.
// For complete instructions, tutorials, and further information, visit:
// https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
#include <DIYables_Keypad.h>
#include "Arduino_RouterBridge.h"
const int ROW_NUM = 4;
const int COLUMN_NUM = 4;
char keys[ROW_NUM][COLUMN_NUM] = {
{ '1', '2', '3', 'A' },
{ '4', '5', '6', 'B' },
{ '7', '8', '9', 'C' },
{ '*', '0', '#', 'D' }
};
byte pin_rows[ROW_NUM] = { 9, 8, 7, 6 };
byte pin_column[COLUMN_NUM] = { 5, 4, 3, 2 };
DIYables_Keypad keypad = DIYables_Keypad(makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM);
char last_key = 0;
String get_key(String arg) {
char key = last_key;
last_key = 0;
if (key == 0)
return "none";
return String(key);
}
String get_status(String arg) {
if (last_key == 0)
return "No key pressed";
return "Last key: " + String(last_key);
}
void setup() {
Bridge.begin();
Monitor.begin();
Bridge.provide("get_key", get_key);
Bridge.provide("get_status", get_status);
Monitor.println("Arduino UNO Q Keypad 4x4 Bridge ready");
}
void loop() {
char key = keypad.getKey();
if (key) {
last_key = key;
Monitor.println("Key pressed: " + String(key));
}
}
Python Code (Bridge)
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
*/
# COPYRIGHT newbiely.com
# AUTHOR: newbiely
# This code is made available for public use without restriction.
# For complete instructions, tutorials, and further information, visit:
# https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
from arduino.app_utils import *
import time
def loop():
result = Bridge.call("get_key")
if result != "none":
print(f"Key pressed: {result}")
else:
print("No key pressed")
time.sleep(0.2)
App.run(user_loop=loop)
Detailed Instructions
- Connect: Wire the 4x4 keypad to the Arduino UNO Q as shown in the wiring diagram.
- Open Arduino App Lab: Launch Arduino App Lab and wait for the board to be detected.
- Create a new App: Click Create New App, name it Keypad4x4Bridge, then click Create.
- Paste the MCU sketch: Copy the MCU Bridge code above and paste it into sketch/sketch.ino.
- Paste the Python code: Copy the Python Bridge code above and paste it into the Python file in the App.
- Upload: Click the Run button in Arduino App Lab.
- Press keys on the keypad and watch the Python console.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] Arduino UNO Q Keypad 4x4 Bridge ready
[2026-04-29 09:00:05] Key pressed: A
[2026-04-29 09:00:08] Key pressed: #
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:03] No key pressed
[2026-04-29 09:00:05] Key pressed: A
[2026-04-29 09:00:07] No key pressed
[2026-04-29 09:00:08] Key pressed: #
Telegram
Get Telegram notifications when a key is pressed on the 4x4 keypad — useful for remote access systems, event triggers, or PIN-code alerts.
MCU sketch: Keep the same MCU sketch from the previous Bridge section.
Python Code (Telegram)
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
*/
# COPYRIGHT newbiely.com
# AUTHOR: newbiely
# This code is made available for public use without restriction.
# For complete instructions, tutorials, and further information, visit:
# https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-keypad-4x4
from arduino.app_utils import *
import requests
import time
TELEGRAM_BOT_TOKEN = "YOUR_TELEGRAM_BOT_TOKEN"
CHAT_ID = "YOUR_CHAT_ID"
last_update_id = 0
def get_updates():
global last_update_id
url = f"https://api.telegram.org/bot{TELEGRAM_BOT_TOKEN}/getUpdates"
params = {"offset": last_update_id + 1, "timeout": 5}
try:
response = requests.get(url, params=params, timeout=10)
data = response.json()
if data["ok"]:
return data["result"]
except Exception as e:
print(f"Error getting updates: {e}")
return []
def send_message(chat_id, text):
url = f"https://api.telegram.org/bot{TELEGRAM_BOT_TOKEN}/sendMessage"
payload = {"chat_id": chat_id, "text": text}
try:
requests.post(url, data=payload, timeout=10)
except Exception as e:
print(f"Error sending message: {e}")
def loop():
global last_update_id
# Poll keypad and notify on key press
result = Bridge.call("get_key")
if result != "none":
msg = f"Key pressed: {result}"
print(msg)
send_message(CHAT_ID, msg)
# Handle incoming Telegram commands
updates = get_updates()
for update in updates:
last_update_id = update["update_id"]
if "message" not in update:
continue
message = update["message"]
chat_id = message["chat"]["id"]
text = message.get("text", "").strip()
print(f"Received: {text}")
if text == "/start":
send_message(chat_id,
"Arduino UNO Q Keypad 4x4 Bot\n"
"/key - Read the last key pressed\n"
"/status - Get keypad status")
elif text == "/key":
result = Bridge.call("get_key")
if result != "none":
send_message(chat_id, f"Key pressed: {result}")
else:
send_message(chat_id, "No key pressed")
elif text == "/status":
result = Bridge.call("get_status")
send_message(chat_id, result)
else:
send_message(chat_id, "Unknown command. Send /start for help.")
time.sleep(0.2)
App.run(user_loop=loop)
Detailed Instructions
- Replace YOUR_TELEGRAM_BOT_TOKEN with your actual bot token from BotFather.
- Replace YOUR_CHAT_ID with your Telegram chat ID.
- Paste this Python code into your App's Python file (keep the same MCU sketch).
- Click the Run button. Press keys on the keypad — your Telegram chat will receive alerts automatically.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:15:00] Waiting for Telegram messages...
[2026-04-29 09:15:05] Key pressed: B
[2026-04-29 09:15:20] Received: /key
[2026-04-29 09:15:35] Key pressed: D
Telegram
12:45
Welcome to Telegram!
ArduinoBot
10:19
Chatting with Arduino...
BotFather
Yesterday
Your bot has been created.
ArduinoBot
bot
OpenClaw
...OPENCLAW
OpenClaw support for Arduino UNO Q Keypad 4x4 is coming soon.
...OPENCLAW
Project Ideas
You can build many creative projects using the 4x4 keypad with Arduino UNO Q:
- Remote PIN Code Lock: User enters a PIN on the keypad; the MCU validates it and controls a relay or solenoid lock, while the MPU sends a Telegram alert on success or failure
- Function Key Controller: Use keys A–D as function shortcuts — each triggers a different IoT action (e.g., A = lights on, B = lights off, C = fan on, D = alarm)
- Calculator Interface: Build a simple calculator where the user enters two numbers and an operator via the keypad, and the result appears on the Serial Monitor or LCD
- Telegram-Triggered Keypad Logger: All key presses are automatically forwarded to a Telegram group for remote monitoring of a physical location
- Multi-User Access System: Assign different PINs to different users — the MPU logs each successful login with a username and timestamp via Telegram
Challenge Yourself
Ready to go further with the 4x4 keypad on Arduino UNO Q? Try these challenges:
- Easy: Modify the MCU sketch to turn an LED on when key A is pressed and off when key B is pressed.
- Medium: Implement a full password system in Python: accumulate key presses received via Bridge, check the input when # arrives, and send a Telegram message with "Access granted" or "Access denied".
- Advanced: Build a multi-user keypad access system — store two different PINs in Python; when either PIN is entered correctly on the keypad, the MCU activates a relay and the MPU logs the event with a timestamp and sends a Telegram notification identifying which PIN was used.