ESP32 C3 Super Mini - Keypad - Electromagnetic Lock
Build a simple password door lock with an ESP32 C3 Super Mini, a 3x4 keypad and an electromagnetic lock. When the password is correct, the ESP32 C3 Super Mini opens the lock through a relay. A second sketch opens it for 5 seconds and then locks it again, without using the delay() function.
In this tutorial, you'll learn:
- How to wire a keypad, a relay and an electromagnetic lock to the ESP32 C3 Super Mini
- How to read a password from the keypad
- How to accept multiple passwords in one sketch
- How to unlock the door when the password is correct
- How to lock the door again after 5 seconds, without delay()
Hardware Preparation
Or you can buy the following kits:
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
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Overview of Keypad and Electromagnetic Lock
A keypad is an input pad that sends key presses to the board, and an electromagnetic lock is a magnet that holds a door closed while it has power.
Key Features:
- Keypad: 12 keys in 4 rows and 3 columns, with no power pin.
- Electromagnetic lock: No moving parts. It locks with magnetic force.
- Relay: Lets the 3.3V GPIO pin switch the 12V lock power safely.
- Fail-safe: The electromagnetic lock opens when its power is cut.
Technical Specifications:
- Keypad pins: 7 (R1, R2, R3, R4, C1, C2, C3).
- Lock power: 12V in this tutorial, from the power adapter.
- Relay module power: 5V from the board.
- Control logic: Pin HIGH = lock powered = door locked. Pin LOW = lock not powered = door unlocked.
Pinout:
- R1 to R4 pins: The 4 row pins of the keypad.
- C1 to C3 pins: The 3 column pins of the keypad.
- Relay IN pin: The control signal from the ESP32 C3 Super Mini.
- Relay COM and NO pins: The switch that carries the 12V lock power.
- Lock wires: Two wires that take the 12V power.
New to these parts? Learn more about their pinouts, how they work and how to program them here:
- ESP32 C3 Super Mini - Keypad tutorial
Wiring Diagram
Connect the keypad to 7 GPIO pins, and connect the lock through the relay.
- Note: Never connect the electromagnetic lock directly to a GPIO pin. Always use the relay.
- Note: Disconnect all power before you change any wire.
- Note: Check that your power adapter matches the voltage and current of your lock.
- Note: Do not use GPIO8 (built-in LED), GPIO9 (boot pin), GPIO20 or GPIO21 (Serial Monitor UART).
This image is created using Fritzing. Click to enlarge image
| Component Pin | ESP32 C3 Super Mini Pin |
|---|---|
| Keypad R1 | GPIO2 |
| Keypad R2 | GPIO3 |
| Keypad R3 | GPIO4 |
| Keypad R4 | GPIO5 |
| Keypad C1 | GPIO6 |
| Keypad C2 | GPIO10 |
| Keypad C3 | GPIO1 |
| Relay IN | GPIO7 |
| Relay VCC | 5V |
| Relay GND | GND |
The 12V side does not touch the board:
| Lock Circuit Pin | Connect To |
|---|---|
| Relay COM | 12V Power + |
| Relay NO | Lock Wire 1 |
| Lock Wire 2 | 12V Power - |
※ NOTE THAT:
The relay stays on GPIO7, the same pin as the electromagnetic lock tutorial. So the keypad columns here are GPIO6, GPIO10 and GPIO1, which is a little different from the keypad tutorial.
WARNING
The ESP32 C3 Super Mini works at 3.3V logic only. Never connect a keypad pin to 5V or to 12V. It can damage the board.
ESP32 C3 Super Mini Code - Unlock the Electromagnetic Lock if the Password Is Correct
This sketch opens the electromagnetic lock when you type a correct password.
What This Code Does:
- Locks the door at startup by setting GPIO7 HIGH.
- Saves 3 passwords: 1234, 56789 and 901234.
- Adds each pressed key to a String called the input password.
- Checks the input password when you press "#".
- Sets GPIO7 LOW to unlock the door if the password is correct.
/*
* This ESP32 C3 Super Mini code was developed by newbiely.com
*
* This ESP32 C3 Super Mini code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/esp32-c3/esp32-c3-super-mini-keypad-electromagnetic-lock
*/
#include <Keypad.h>
#define RELAY_PIN 7 // The ESP32 C3 SuperMini pin GPIO7 connected to the relay
#define ROW_NUM 4 // keypad four rows
#define COLUMN_NUM 3 // keypad three columns
char keys[ROW_NUM][COLUMN_NUM] = {
{'1', '2', '3'},
{'4', '5', '6'},
{'7', '8', '9'},
{'*', '0', '#'}
};
byte pin_rows[ROW_NUM] = {2, 3, 4, 5}; // The ESP32 C3 SuperMini pin GPIO2, GPIO3, GPIO4, GPIO5 connected to the row pins
byte pin_column[COLUMN_NUM] = {6, 10, 1}; // The ESP32 C3 SuperMini pin GPIO6, GPIO10, GPIO1 connected to the column pins
Keypad keypad = Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM );
const String password_1 = "1234"; // change your password here
const String password_2 = "56789"; // change your password here
const String password_3 = "901234"; // change your password here
String input_password;
void setup() {
Serial.begin(115200);
input_password.reserve(32); // maximum password size is 32, change if needed
pinMode(RELAY_PIN, OUTPUT); // initialize pin as an output.
digitalWrite(RELAY_PIN, HIGH); // lock the electromagnetic lock
}
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 => unlock");
digitalWrite(RELAY_PIN, LOW);
} 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
}
}
}
Detailed Instructions
- New to ESP32 C3 Super Mini? Complete our Getting Started with ESP32 C3 Super Mini tutorial first to set up your development environment.
- Wire the parts: Follow the wiring diagram and the tables above.
- Connect the board: Plug the ESP32 C3 Super Mini into your PC with a USB Type-C cable.
- Open the IDE: Start the Arduino IDE on your PC.
- Select the board: Make sure ESP32 C3 Super Mini is selected in Tools > Board.
- Select the port: Pick the COM port of your board in Tools > Port.
- Open Library Manager: Click the Libraries icon on the left bar of the Arduino IDE.
- Search for the library: Type keypad, then find the Keypad library by Mark Stanley, Alexander Brevig.
- Install the library: Click the Install button.
- Search for Keypad created by Mark Stanley, Alexander Brevig and click the Install button.
1
void setup() {
- Copy the code: Copy the code above and open it in the Arduino IDE.
- Upload the code: Click the Upload button to send the code to the ESP32 C3 Super Mini.
- Open Serial Monitor: Set the baud rate to 115200.
- Try a wrong password: Press 8123 and then press #.
- Try the right password: Press 1234 and then press #.
- Check the result: Read the Serial Monitor and look at the state of the electromagnetic lock.
- Pro Tip: This sketch never locks the door again by itself. Press the reset button on the board to lock it again.
8
Serial.println("Hello World!");
Message (Enter to send message to 'ESP32C3 Dev Module' on 'COM15')
New Line
9600 baud
8
1
2
3
#
The password is incorrect, try again
1
2
3
4
#
The password is correct => unlock
Code Explanation
The authorized passwords are saved in the code, and the typed keys are kept in a String called the input password.
- Normal key: The key is added to the end of the input password.
- "*" key: The input password is cleared. Use it to start or restart typing.
- "#" key: The input password is compared with the saved passwords.
- Match: The ESP32 C3 Super Mini sets the relay pin LOW, and the electromagnetic lock opens.
- After "#": The input password is cleared for the next try, whether it was correct or not.
ESP32 C3 Super Mini Code - Unlock the Electromagnetic Lock for a Period of Time
This sketch opens the electromagnetic lock for 5 seconds when the password is correct, and then locks it again.
What This Code Does:
- Uses the same keypad code and the same 3 passwords as the first sketch.
- Controls the relay on GPIO7 with the ezOutput library.
- Starts a 5-second pulse with relay.pulse() when the password is correct.
- Keeps reading the keypad during those 5 seconds, because it does not use delay().
- Sets the unlock time with UNLOCK_TIME, in milliseconds.
/*
* This ESP32 C3 Super Mini code was developed by newbiely.com
*
* This ESP32 C3 Super Mini code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/esp32-c3/esp32-c3-super-mini-keypad-electromagnetic-lock
*/
#include <Keypad.h>
#include <ezOutput.h>
#define UNLOCK_TIME 5000 // in milliseconds
#define RELAY_PIN 7 // The ESP32 C3 SuperMini pin GPIO7 connected to the relay
#define ROW_NUM 4 // keypad four rows
#define COLUMN_NUM 3 // keypad three columns
char keys[ROW_NUM][COLUMN_NUM] = {
{'1', '2', '3'},
{'4', '5', '6'},
{'7', '8', '9'},
{'*', '0', '#'}
};
byte pin_rows[ROW_NUM] = {2, 3, 4, 5}; // The ESP32 C3 SuperMini pin GPIO2, GPIO3, GPIO4, GPIO5 connected to the row pins
byte pin_column[COLUMN_NUM] = {6, 10, 1}; // The ESP32 C3 SuperMini pin GPIO6, GPIO10, GPIO1 connected to the column pins
Keypad keypad = Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM );
ezOutput relay(RELAY_PIN);
const String password_1 = "1234"; // change your password here
const String password_2 = "56789"; // change your password here
const String password_3 = "901234"; // change your password here
String input_password;
void setup() {
Serial.begin(115200);
input_password.reserve(32); // maximum password size is 32, change if needed
relay.high(); // lock the electromagnetic lock
}
void loop() {
relay.loop(); // MUST call the loop() function first
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 => unlock");
relay.high(); // set high before making a low pulse
relay.pulse(UNLOCK_TIME); // deactivate the electromagnetic lock during UNLOCK_TIME duration
} 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
}
}
}
Detailed Instructions
- Install the library: Open the Library Manager, search for ezOutput, then click Install.
- Search for ezOutput created by ArduinoGetStarted.com and click the Install button.
1
void setup() {
- Upload the code: Copy the code above, paste it into the Arduino IDE, and click Upload.
- Open Serial Monitor: Set the baud rate to 115200.
- Test it: Press 1234 and then press #.
- Watch the lock: The door opens, and it locks again after 5 seconds.
- Pro Tip: The ezOutput library manages the time without blocking the code. Change UNLOCK_TIME to keep the door open for longer.
8
Serial.println("Hello World!");
Message (Enter to send message to 'ESP32C3 Dev Module' on 'COM15')
New Line
9600 baud
5
6
7
8
#
The password is incorrect, try again
5
6
7
8
9
#
The password is correct => unlock
Application/Project Ideas
A keypad and an electromagnetic lock on the ESP32 C3 Super Mini can protect many real doors.
- Home Door Lock: Open a front or back door with a PIN code.
- Office Access: Give each person their own password for one room.
- Tutorial Security: Keep tools and machines behind a locked door.
- Storage Cabinet: Lock a cabinet or a tool locker with a small electromagnetic lock.
- Exit Timer: Open a door for a few seconds, and then lock it again by itself.
Challenge Yourself
Try these small projects to improve your ESP32 C3 Super Mini keypad electromagnetic lock.
- Easy: Change the passwords to your own codes and test them.
- Easy: Change UNLOCK_TIME so the door stays open for 10 seconds.
- Medium: Add a buzzer that beeps when the password is wrong.
- Medium: Block the keypad for 30 seconds after three wrong tries.
- Advanced: Save the passwords in flash memory, and add a key sequence to change them.
- Advanced: Use the WiFi of the ESP32 C3 Super Mini to send you an alert after many wrong tries.