How to set up an Access Point, and what it is good for
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src/main.cpp
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src/main.cpp
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//--------------------------------------------------------------------------------------------------------------------------//
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// Handling Interrupts correctly
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// Setting up an Access Point hosted by the ESP32
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//--------------------------------------------------------------------------------------------------------------------------//
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// What are Interrupts? //
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// You can see them as certain parts of a programm reacting to a condition at ANY time and place your programm is currently in.
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// You use them to time reads for example, or for signals, etc etc.
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// What is the difference between an Access Point and using the ESP as a client? //
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// Well, there's a big difference as to how either work, and what is needed. As an Access Point, you can create your own little "network" hosted
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// over the small WLAN module on the developing board. That let's you access a website on the ESP for example, without
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// having to go over any of your internet provider's servers since it's purely local.
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// When hosting an Access Point, you CANNOT log into another Wlan network. Clients (for example your phone) can log into the one on the ESP though.
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// If you want to use an async Webserver, that works better with the use of a router inbetween, and has more advantages all in all.
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// If no internet connection is required and it's for little displayment, a local Access Point should be enough.
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#include <Arduino.h>
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// Load Wifi library //
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#include <WiFi.h>
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// Set your network credentials (you are entirely free to choose anything) //
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const char* _ssid = "ESP32-Access-Point"; // for example
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const char* _password = "1234IamAPassword"; // that's a bad example, but you get the gist
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// Set up instance and the right port (default: 80) //
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WiFiServer server(80);
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// String to save the http adress in //
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String _http = "";
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// State variable for the example following in the loop() function later //
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String _output_state = "off";
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void setup()
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{
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// Initializing the timer //
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void IRAM_ATTR onTimer();
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Serial.println("Setting up access point...");
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WiFi.softAP(_ssid, _password);
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IPAddress _IP = WiFi.softAPIP(); // You can see what is hosted on the ESP over this IP address.
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Serial.print("AP IP Address: ");
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Serial.println(_IP);
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hw_timer_t *My_timer = 0;
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My_timer = timerBegin(0, 80, true);
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timerAttachInterrupt(My_timer, &onTimer, true);
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timerAlarmWrite(My_timer, 5000, true);
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timerAlarmEnable(My_timer);
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// This is crutial and has to be in the setup.
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// You can change the frequency as to when it gets called (Check it out online), as well as the reason.
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// You can attach a timer to a Pin for example as well.
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// That would look something like this:
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//
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// pinMode(SWITCH_PIN, INPUT_PULLUP);
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// attachInterrupt(digitalPinToInterrupt(SWITCH_PIN), switchChanged, CHANGE);
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// But it's not necessary if you're using Interrupts as a timer.
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server.begin(); // starts WiFi server.
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}
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void loop()
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{
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// Listen for any incoming clients, you can also create a thread extra for this if little processing power is needed //
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WiFiClient _client = server.available();
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// If that is the case, make sure to keep the service running. It should not be stopped or interrupted at all if the programm is still running,
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// I'd advice to use an exeption / interrupt that is listening in on whether or not a new client or http request has been received.
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// Be careful with that in general if you try it.
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}
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// Handling the function //
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void IRAM_ATTR onTimer()
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if(_client)
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{
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// This function is called when the interrupt has been triggered.
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String _current_line = "";
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while(_client.connected()) // As long as the client is connected...
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{
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if(_client.available()) // Checks whether or not there is bites to read from.
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{
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char _c = _client.read(); // reads a single bite.
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_http += _c; // assembling the full http request one by one.
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// Keep your operations in here as SIMPLE as possible, and as quick as possible.
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// DO NOT do heavy processing on this threat, or perform long lasting operations.
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// ^ That includes any sort of printing or writing to a file for example.
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// Also refrain from using while(1) AT ALL COSTS. Short lasting while loops are fine, but also make sure they don't take too long to break out again.
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if(_c != 10) // Listen in for LF (new line / line feat) since that is
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// a signal for the end of the request.
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// (Side note: Using '\n' here should technicall work here, but can create some errors.)
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// (Use 10 (ASCII) instead to avoid any misleading errors.)
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{
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// Send a response here, since every request needs a response.
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// If something went wrong, be sure to send an error message instead of nothing.
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// Replying: //
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if(_current_line.length() == 0)
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{
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// HTTP headers always start a certain way. So be sure to keep the following format.
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_client.println("HTTP/1.1 200 OK");
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_client.println("Content-type:text/html");
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_client.println("Connection: close");
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_client.println();
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// And there you go, a correct response that a client can work with!
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// Now you can technically compute whatever changes the client might have requested,
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// whether that was a press of a button or a press on a link. Any action needs to be responded to,
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// or else one might end up in the void of white like a blank page, or nothing happens.
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// The following is an example of how you would process requests with a html button.
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// NOTE! This is html code written inside a C/C++ code. It's far from optional, and SPIFFS is therefor recommended if a
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// seperate html & css file is prefered. You can read about that in the tutorial branch to the Async Server.
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// For now, this is purely for demonstration.
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// Handling the change of the example button //
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if (_http.indexOf("GET Button on") >= 0)
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{
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Serial.println("Button turned on");
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_output_state = "on";
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// digitalWrite(PIN, HIGH); // == how you would pull a Pin up when the button activates.
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}
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else if (_http.indexOf("GET Button off") >= 0)
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{
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Serial.println("Button turned off");
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_output_state = "off";
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// digitalWrite(PIN, LOW); // again for example.
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}
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// That is basically it for now regarding simple interrupts.
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// It's useful regarding sending data only like every 5 minutes, or every 10 milliseconds for example. Use it carefully, and happy coding. :D
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// Displaying the site //
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_client.println("<!DOCTYPE html><html>");
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_client.println("<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">");
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_client.println("<link rel=\"icon\" href=\"data:,\">");
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// Set up a button //
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_client.println("<style>html { font-family: Helvetica; display: inline-block; margin: 0px auto; text-align: center;}");
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_client.println(".button { background-color: #4CAF50; border: none; color: white; padding: 16px 40px;");
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_client.println("text-decoration: none; font-size: 30px; margin: 2px; cursor: pointer;}");
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_client.println("</style></head>"); // closes the style tag.
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if (_output_state=="off")
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{
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_client.println("<p><a href=\"Button on\"><button class=\"button\">ON</button></a></p>");
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}
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else
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{
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_client.println("<p><a href=\"Button off\"><button class=\"button button2\">OFF</button></a></p>");
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}
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// End the HTTP response with a LF as well //
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_client.println();
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break;
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}
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else // received a LF, clear the current line for input.
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{
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_current_line = "";
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}
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} // end of if()
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else if(_c != 13) // Handles the exeption for if you got anything but a carriage return.
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// NOTE! Technically, '\r' should also work, but like '\n', it can cause issues.
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// (Once more use 13 (ASCII) instead)
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{
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_current_line += _c;
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}
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} // end of if()
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} // end of while()
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// Clear the request variable for later use //
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_http = "";
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// Close the connection to the client //
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_client.stop();
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Serial.println("Client disconnected.");
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Serial.println();
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// For every time the loop repeats, a new client and a new http request is being processed.
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}
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}
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// As said, the example is a tedious an impractical way to host reactive html code.
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// Yet, it's enough for simple and fast displaying of values over a local WiFi Webserver.
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// Still, since it needs an entire thread to run, it's far from the ideal way.
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