ESP32 Relay Web Server

Contributors: Elias The Sparkiest
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The goal of this project is to have a website hosted on an ESP32 that controls any relay controlled device connected to a local network and keeps a dynamically updated state of those devices. The website must look good but more importantly, be responsive. The goal of this tutorial is to be instructive in the topics associated with each component that make up the project. Clearly it will outline the steps to get the project up and running, but it will also delve into each concept with some depth to give you more information on how this project works; with some attempt to keep you, the reader, from falling asleep. Through out this tutorial "device" is synonymous with "relay" because a relay will be controlling the device.

This is a continuation of the Infrared tripwires to automate light switching and The ESP32 Web Server blog posts. After achieving the primary goal outlined above, there will be another section added to go over how to integrate the IR tripwires as a "user" controlling the relays. Let's go over what each individual piece of the project looks like.

How - ESP32 and SPIFFS

Using an ESP32 or ESP8266 and utilizing the SPIFFS Filesystem (SPI Flash File System) library, the ESP module suddenly has a file system! This opens up many possibilities because we can now store and open webpage files, small images, and files for tracking states of the devices. This tutorial uses an ESP32 in place of an ESP8266 because of it's larger memory capacity. More memory increases our file size capabilities and gives the micro-controller longer life because we're not butting up against its maximum storage capacity.

Responsiveness - ESPAsync and Websockets

The ESPAsync Library includes example code which provides the basis for the tutorial's source code. The ESPAsync library, as the name suggests, manages asynchronous web requests. This is important; the website needs to handle a case in which two people are on the webpage at the same time, or when someone trips the IR tripwire while someone is on the webpage. Because the website is asynchronous by design that means it will queue requests in the background without explicit code in the Arduino sketch and can change the state of the relay and the website's indicators as requested.

"State Machine" - ArduinoJson and JSON files

The state of each device will be kept in a JSON file within the SPIFFS file system. The JSON file will be very simple:

    "relay_states": [0,0,0,0]
    "password" : "password"


Alternatively a simple text file could do the same thing. So why a JSON file? JSON being a markup language is designed to organize data into parsable objects which makes the interaction with JSON files more intuitive. In addition WiFi network names and passwords can also be saved within other files without having to modify the Arduino Sketch. To parse the JSON file we'll leverage the very well written and very well documented ArduinoJson Library.

The Feel - BootStrap, CSS and Javascript

The web page's theme and its' scalability from desktop to mobile phone will be made possible with Bootstrap - a toolkit for HTML, JS, and CSS. The tutorial will outline how to keep the file size small and get the most out of the simplicity of the Bootstrap toolkit.