ESP32 - Button Control Electromagnetic Lock

This tutorial instructs you how to use ESP32 with the button and electromagnetic lock. In detail, we will learn how to use the button to control electromagnetic lock without debouncing and with debouncing. Each time button is pressed, unlock the door for 10 seconds and then lock the door.

Hardware Used In This Tutorial

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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Introduction to Button and Electromagnetic Lock

We have specific tutorials about electromagnetic lock and button. Each tutorial contains detailed information and step-by-step instructions about hardware pinout, working principle, wiring connection to ESP32, ESP32 code... Learn more about them at the following links:

Wiring Diagram

wiring diagram between esp32 button electromagnetic lock

This image is created using Fritzing. Click to enlarge image

ESP32 Code - Button Controls Electromagnetic Lock Without Debouncing

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-button-controls-electromagnetic-lock */ #define BUTTON_PIN 22 // ESP32 pin GIOP22 connected to button's pin #define RELAY_PIN 27 // ESP32 pin GIOP27 connected to relay's pin // The below are variables, which can be changed 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 Instructions

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
  • Do the wiring as above image.
  • Connect the ESP32 board to your PC via a micro USB cable
  • Open Arduino IDE on your PC.
  • Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
  • Copy the above code and paste it to Arduino IDE.
  • Compile and upload code to ESP32 board by clicking Upload button on Arduino IDE
  • Put the armature plate close to electromagnet.
  • Press button one time.
  • See the attraction between armature plate and electromagnet during 10 seconds.

Line-by-line Code Explanation

The above ESP32 code contains line-by-line explanation. Please read the comments in the code!

In practice, we need to debounce for the button. The next part will show how to debounce for the button.

ESP32 Code - Button Controls Electromagnetic Lock With Debouncing

Why need to debounce for the button? ⇒ see ESP32 - Button Debounce tutorial

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-button-controls-electromagnetic-lock */ #include <ezButton.h> #define BUTTON_PIN 22 // ESP32 pin GIOP22 connected to button's pin #define 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 Instructions

  • 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.
  • Compile and upload code to ESP32 board by clicking Upload button on Arduino IDE
  • Put the armature plate close to electromagnet.
  • Press button one time.
  • See the attraction between armature plate and electromagnet during 10 seconds.

※ NOTE THAT:

Since the above code used the delay() function, we do not need to do debouncing for the button. However, We still provide the code with debouncing in case you modify this code and do not use the delay() function

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