Arduino - Keypad - Servo Motor

In this tutorial, we are going to learn how to use a keypad, servo motor, and Arduino together:

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×Servo Motor
1×5V Power Adapter
1×DC Power Jack
n×Jumper Wires
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About Keypad and Servo Motor

If you do not know about keypad and servo motor (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

Arduino keypad servo motor wiring diagram

Image is developed using Fritzing. Click to enlarge image

Arduino Code - rotates Servo Motor if the password is correct

The below code turns the servo motor to 90° for 5 seconds if the password is correct. After 5 seconds, it turns the servo motor to 0°.

/* * Created by * * This example code is in the public domain * * Tutorial page: */ #include <Keypad.h> #include <Servo.h> #define ROW_NUM 4 // four rows #define COLUMN_NUM 4 // four columns #define SERVO_PIN A0 // // the Arduino pin, which connects to the servo motor Servo servo; // servo motor 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}; //connect to the row pinouts of the keypad byte pin_column[COLUMN_NUM] = {5, 4, 3, 2}; //connect to the column pinouts of the keypad Keypad keypad = Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM ); const String password_1 = "ABC1234"; // change your password here const String password_2 = "5642B"; // change your password here const String password_3 = "9765"; // change your password here String input_password; int angle = 0; // the current angle of servo motor unsigned long lastTime; void setup() { Serial.begin(9600); input_password.reserve(32); // maximum password size is 32, change if needed servo.attach(SERVO_PIN); servo.write(0); // rotate servo motor to 0° lastTime = millis(); } void loop() { char key = keypad.getKey(); if (key) { Serial.println(key); if (key == '*') { input_password = ""; // reset the input password } else if (key == '#') { if (input_password == password_1 || input_password == password_2 || input_password == password_3) { Serial.println("The password is correct, rotating Servo Motor to 90°"); angle = 90; servo.write(angle); lastTime = millis(); } else { Serial.println("The password is incorrect, try again"); } input_password = ""; // reset the input password } else { input_password += key; // append new character to input password string } } if (angle == 90 && (millis() - lastTime) > 5000) { // 5 seconds angle = 0; servo.write(angle); Serial.println("Rotating Servo Motor to 0°"); } }

Quick Steps

  • Connect Arduino to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • On Arduino IDE, Go to Tools Manage Libraries
  • Arduino add library
  • Search “keypad”, then find the keypad library by Mark Stanley, Alexander Brevig
  • Click Install button to install keypad library.
  • Arduino keypad library
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
  • Arduino IDE Upload Code
  • Press 12345#
  • Press 5642B#
  • See the result on Serial Monitor and the state of servo motor
  • COM6
    The password is incorrect, try again The password is correct, rotating Servo Motor to 90° Rotating Servo Motor to 0°
    Autoscroll Show timestamp
    Clear output
    9600 baud  

Code Explanation

Authorized passwords are pre-defined in the Arduino code.

A string is used to store the password inputted by users, called input_password. In keypad, two keys (* and #) are used for special purposes: clear password and terminate password. When a key on keypad is pressed:

  • If the pressed key is not one of two special keys, it is appended to the input_password
  • If the pressed key is *, input_password is clear. You can use it to start or re-start inputing the password
  • If the pressed key is #:
    • The input_password is compared with the pre-defined passwords. If it matched with one of the pre-defined passwords, rotate the servo motor to 90°.
    • Regardless the password is correct or not, the input_password is clear for the next input

Video Tutorial

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