ESP32 - Button Control Electromagnetic Lock

The tutorial uses electromagnetic lock to unlock/lock the door, The code will includes two main parts:

When button is pressed, unlock the door for 10 seconds and then lock the door.

Hardware Required

1×ESP-WROOM-32 Dev Module
1×Micro USB Cable
1×Electromagnetic Lock
1×Relay
1×12V Power Adapter
1×Button
1×Breadboard
n×Jumper Wires
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About Button and Electromagnetic Lock

If you do not have knowledge of electromagnetic lock and button (pinout, how they work, how to connect them to ESP32, how to program for them...), learn about them in the following tutorials:

Wiring Diagram

ESP32 Button Electromagnetic Lock Wiring Diagram

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ESP32 Code - Button Controls Electromagnetic Lock Without Debouncing

/* * Created by esp32io.com * * This example code is in the public domain * * Tutorial page: https://esp32io.com/tutorials/esp32-button-controls-electromagnetic-lock */ // constants won't change const int BUTTON_PIN = 22; // ESP32 pin GIOP22 connected to button's pin const int RELAY_PIN = 27; // ESP32 pin GIOP27 connected to relay's pin // variables will change: int lastButtonState; // the previous state of button int currentButtonState; // the current state of button void setup() { Serial.begin(9600); // initialize serial pinMode(BUTTON_PIN, INPUT_PULLUP); // set ESP32 pin to input pull-up mode pinMode(RELAY_PIN, OUTPUT); // set ESP32 pin to output mode digitalWrite(RELAY_PIN, HIGH); // lock the door currentButtonState = digitalRead(BUTTON_PIN); } void loop() { lastButtonState = currentButtonState; // save the last state currentButtonState = digitalRead(BUTTON_PIN); // read new state if(lastButtonState == HIGH && currentButtonState == LOW) { Serial.println("The button is pressed"); digitalWrite(RELAY_PIN, LOW); // unlock the door in 10 seconds delay(10000); // 10 seconds digitalWrite(RELAY_PIN, HIGH); // lock the door again } }

Quick Steps

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE
  • Connect the ESP32 board to your PC via a micro USB cable
  • Open Arduino IDE, select the right ESP32 board and COM port
  • Copy the above code and paste it to Arduino IDE
  • Click Upload button on Arduino IDE to compile and upload code to ESP32 board
  • Put the armature plate close to electromagnet.
  • Press button one time.
  • See the attraction between armature plate and electromagnet during 10 seconds.

Code Explanation

Read the line-by-line explanation in comment lines of code!

※ NOTE THAT:

In practice, the above code does not work correctly sometimes. To make it always work correctly, we need to debounce for the button. Debouncing for the button is not easy for beginners. Fortunately, thanks to the ezButton library, We can do it easily.

ESP32 Code - Button Controls Electromagnetic Lock With Debouncing

Why do we need debouncing? ⇒ see ESP32 - Button Debounce tutorial

/* * Created by esp32io.com * * This example code is in the public domain * * Tutorial page: https://esp32io.com/tutorials/esp32-button-controls-electromagnetic-lock */ #include <ezButton.h> // constants won't change const int BUTTON_PIN = 22; // ESP32 pin GIOP22 connected to button's pin const int RELAY_PIN = 27; // ESP32 pin GIOP27 connected to relay's pin ezButton button(BUTTON_PIN); // create ezButton object that attach to pin 7; void setup() { Serial.begin(9600); // initialize serial pinMode(RELAY_PIN, OUTPUT); // set ESP32 pin to output mode button.setDebounceTime(50); // set debounce time to 50 milliseconds digitalWrite(RELAY_PIN, HIGH); // lock the door } void loop() { button.loop(); // MUST call the loop() function first if(button.isPressed()) { Serial.println("The button is pressed"); digitalWrite(RELAY_PIN, LOW); // unlock the door in 10 seconds delay(10000); // 10 seconds digitalWrite(RELAY_PIN, HIGH); // lock the door again } }

Quick Steps

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE
  • Install ezButton library. See How To
  • Copy the above code and paste it to Arduino IDE
  • Click Upload button on Arduino IDE to compile and upload code to ESP32 board
  • Put the armature plate close to electromagnet.
  • Press button one time.
  • See the attraction between armature plate and electromagnet during 10 seconds.

※ NOTE THAT:

In the above code, we used the delay function. Therefore, we do not need to debouncing for button. However, We still provide the code with debouncing just in case you want to do more tasks without using delay function. See How to use millis() instead of delay()

Video Tutorial

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Button and Electromagnetic Lock on Commercial Products

※ NOTE THAT:

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