Arduino-esp32 course – Espressif is on the www WebServer vs HttpClient – Chapter 4

As a preamble I wanted to make clear that is not my intention to teach C or C++ here, since they are very good online resources for that, and more to make my point in some easy ways to get the most of espressif/arduino-esp32 Framework.

In chapter 2 it was explained how to connect the ESP32 to WiFi so I thought it would be great to make an additional chapter that makes use of the connection in both directions:

  1. WebServer class – the ESP32 will listen on a port and reply or react to your query
    Additionally, we will use the ESPmDNS class to enable multicast DNS
  2. HttpClient class – it will send a GET or POST request to an endpoint

For the HttpClient I will make a special endpoint that it will be available in a subdomain of fasani.de and it will just answer with the time (HH:MM). Please note that after chapter 3 I will only focus on ESP32 since it was already explained how you can write code that works in both Espressif chips ESP8266 or ESP32 using Platformio environments and #ifdef conditionals.

1. WebServer example: ESP32 listens on port 80

The first example will be very simple and to the point. We will just take as a base what we wrote in chapter 2 to connect to WiFi and we will extend it using WebServer class. Once the ESP32 is online and we got the IP Address in the Serial output we will hit the route: http://ESP_IP_ADDRESS/switch

And in this route, using WebServer event handlers, we are going to toggle a GPIO high and low. Pretty simple, but powerful since if instead of a LED, we could use a relay that turns a 220v light or any other device On/Off via WiFi, so you can control it from any other terminal connected to the same WiFi Network. Using your imagination, you may build multiple endpoints that perform different things using predefined routes and modifying this example.

#include "Arduino.h"
#include <WiFi.h>
#include <ESPmDNS.h>  // multicast DNS
#include <WebServer.h>
#define LED_GPIO 25   // Update to a internal LED or just connect one with a resistance in that GPIO
int lostConnectionCount = 0;
char apName[] = "fasani";
bool switchState = false;
WebServer server(80); // port where we start the server

// Callback see defineServerRouting
void onServerSwitch(){
   switchState = !switchState;
   digitalWrite(LED_GPIO, switchState);
   String switchStatus = "OFF";
   if (switchState) {
     switchStatus = "ON";
   }
   server.send(200, "text/html", switchStatus);
}

void onServerNotFound(){
  Serial.println("404");
  server.send(200, "text/html", "404 this route is not defined on "We could not read the time.\nPlease check in the browser that the given url: %d is correct anddefineServerRouting()");
}

// ROUTING Definitions. Add your server routes here
void defineServerRouting() {
  server.on("/switch", HTTP_GET, onServerSwitch);
  server.onNotFound(onServerNotFound);
}

/** Callback for receiving IP address from AP */
void gotIP(system_event_id_t event) {
  Serial.println("Online. Local IP address:");
  Serial.println(WiFi.localIP().toString());

  MDNS.begin(apName);
  MDNS.addService("http", "tcp", 80);
  Serial.println(String(apName)+".local mDns started");
  defineServerRouting();
  server.begin();

  Serial.println("Server started");
}

/** Callback for connection loss */
void lostCon(system_event_id_t event) {
  ++lostConnectionCount;
  Serial.printf("WiFi lost connection try %d to connect again\n", lostConnectionCount);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  if (lostConnectionCount==4) {
    Serial.println("Cannot connect to the internet. Check your WiFI credentials");
  }
}

void setup() {
  Serial.begin(115200);
  Serial.println("setup() started let's connect to WiFI");
  pinMode(LED_GPIO,OUTPUT);
  Serial.printf("WiFi name: %s\nWiFi pass: %s\n", WIFI_SSID, WIFI_PASS);
// Start our connection attempt
  WiFi.begin(WIFI_SSID, WIFI_PASS);
// Event driven WiFi callbacks
// Setup callback function for successful connection
  WiFi.onEvent(gotIP, SYSTEM_EVENT_STA_GOT_IP);

// Setup callback function for lost connection
  WiFi.onEvent(lostCon, SYSTEM_EVENT_STA_DISCONNECTED);
}

void loop() {
  // Run our server engine
  server.handleClient();
}

Note: Only Linux and Mac support mDNS out of the box. If you use windows you will need to install additional software for that. Now since we use a multicast DNS server if we are using a client that supports it once we upload that code to an ESP32 we could access it from this 2 URLs:

  1. http://ESP_IP_ADDRESS/switch
  2. http://fasani.local/switch

Please note that even that WordPress makes the links above are not clickable and I also used fasani as ApName as shameless self-promotion. Please feel free to change it to your own updating the apName char variable.

This little program will just connect to WiFi, start a mDNS server and a WebServer in port 80, define the route /switch and simply turn a GPIO High and give 3.3v (ON) or Low 0v (OFF) to a GPIO. I just added a function where the routes are defined, since I’m a web developer, and I would like to emulate how other Web frameworks do to keep the routing in a single place. It’s useful, both for the program and for the documentation, to have a single function to place all the actions that your Firmware will support. This example is very simple but it has potential since you can expand it with as many actions you want, and not only turn High or Low a Gpio but also change variables using your server routes, or any other thing you desire.

2. HttpClient: The ESP32 will make a GET request

For this I prepared a very simple endpoint:

http://fs.fasani.de/time.php -> Will return the time in Europe/Berlin as default
http://fs.fasani.de/time.php?tz=America/Los_Angeles will return the time of that timezone

Of course you can use any timezone you want. The source of time.php is just 4 lines and you can put it in any server that supports PHP no matter what version:

<?php
$tz = isset($_GET['tz'])?$_GET['tz']:'Europe/Berlin';
date_default_timezone_set($tz);
echo date("H:i");

So this example will be even easier than number 1. It will simply connect to WiFi and query this URL to print in the Serial output the current time. The applications can be endless, for example, you can return only the hour as an integer, and your program can decide to turn on something depending on the hour.

#include "Arduino.h"
#include <WiFi.h>
#include <HTTPClient.h>
int lostConnectionCount = 0;
HTTPClient http;
String url = "http://fs.fasani.de/time.php?tz=Europe/Berlin";

void gotIP(system_event_id_t event) {
  Serial.println("Online. Local IP address:");
  Serial.println(WiFi.localIP().toString());
  http.begin(url);
  int httpCode = http.GET();  //Make the request
  Serial.printf("http status:%d\n", httpCode);

  if (httpCode == 200) { 
     String response = http.getString();
     Serial.printf("The time now is: %s\n", response);
  } else {
    Serial.printf("We could not read the time.\nPlease check in the browser that the given url: %s is correct and replies with an HTTP 200 OK status", url);
  }
}

void lostCon(system_event_id_t event) {
  ++lostConnectionCount;
  Serial.printf("WiFi lost connection try %d to connect again\n", lostConnectionCount);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  if (lostConnectionCount==4) {
    Serial.println("Cannot connect to the internet. Check your WiFI credentials");
  }
}

void setup() {
  Serial.begin(115200);
  Serial.println("setup() started let's connect to WiFI");
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  WiFi.onEvent(gotIP, SYSTEM_EVENT_STA_GOT_IP);
  WiFi.onEvent(lostCon, SYSTEM_EVENT_STA_DISCONNECTED);
}

void loop() {
}

I hope this two easy examples will serve you to build more powerful things on top. I will be monitoring the commentaries if you want to achieve things that are not explained here.
In the next chapters we will explore more possibilities, based on my last 2 years journey, but also on your feedback.

Arduino-esp32 course – General-purpose input/output (GPIO) – Chapter 3

I want to state here that I’m not an electronics engineer and I know the basics only after years of tinkering and because I use to soldier PCBs for my father since I’m 8 or so. So if there is anything that is not correctly explained just comment and I will try to document it better.
The ESP8266 has 17 GPIO pins (0-16), however, you can only use 11 of them, because 6 pins (GPIO 6 – 11) are used to connect the flash memory chip.
The ESP32 chip has 40 physical GPIO pins. Not all of them can be used and some of them are only input GPIOs meaning you cannot use them for output communication (Refer to your board tech specs fot that) According to Espressif documentation on the ESP32:

  • GPIO 6-11 are usually used for SPI flash.
  • GPIO 34-39 can only be set as input mode and do not have software pullup or pulldown functions.

Electronics ABC
pull-up resistor connects unused input pins to the dc supply voltage, (3.3 Vcc in ESP32) to keep the given input HIGH
pull-down resistor connects unused input pins to ground, (GND 0V) to keep the given input LOW.
Analog-to-Digital Converter (ADC)
The Esp32 integrates 12-bit ADCs and supports measurements on 18 channels (analog-enabled pins). The Ultra low power (ULP-coprocessor) in the ESP32 is also designed to measure voltages while operating in sleep mode, which allows for low power consumption.
Digital-to-Analog Converter (DAC)
Two 8-bit DAC channels can be used to convert two digital signals to two analog voltage outputs. These dual DACs support the power supply as an input voltage reference and can drive other circuits. Dual channels support independent conversions.

A detailed walkthrough over GPIOs and electronics is out-of-scope in this blog post series since it’s a thema on it’s own and I think a engineer could be the best suited to expand on this properly. There are many instructables and videos about it if you are interested in researching more.

So now back to ESP32 Arduino framework coding, let’s use this GPIO information, to declare one as output and blink a LED.

#include "Arduino.h"
// HINT: Many ESP32 boards have an internal LED on GPIO5
// If it's on another PIN just change it here:
int ledGpio = 5; 

void setup() { 
  Serial.begin(115200);
  Serial.println("Hello blinking LED");
  pinMode(ledGpio, OUTPUT);
} 
void loop() { 
  digitalWrite(ledGpio, HIGH); 
  delay(500); 
  digitalWrite(ledGpio, LOW); 
  delay(200); 
}

As a good reference here is the pinMode entry in Arduino documentation. modes can be:

  • INPUT
  • OUTPUT
  • INPUT_PULLUP

This very short program will just set the GPIO5 in output mode and in the loop just turn it HIGH(1) and send 3.3V to the GPIO or LOW(0). Keep in mind that the ESP32 can draw a max. consumtion of about 10 mA per GPIO so always use a resistance (10K or similar) if you connect your own LED or you may damage the board.
Now seeing that the GPIO state is 1 or 0, we can also write this program in a shorter way, let’s give it a second round:

include "Arduino.h"
int ledGpio = 25;
bool ledState = 0; // New bool variable
void setup() {
  pinMode(ledGpio, OUTPUT);
}
void loop() {
  digitalWrite(ledGpio, ledState);
  ledState = !ledState;
  delay(20);
}

We are just doing one digitalWrite per loop now and right after that just redeclaring the variable using the logical NOT operator. That way it will flip between 0 and 1, turning the LED on and off quite fast since we added just a 20 millis delay. So fast is almost always on!
So now we are in this point we can start with the next topic that is called pulse width modulation or PWM.

PWM provides the ability to ‘simulate’ varying levels of power by oscillating the output from the microcontroller. By varying (or ‘modulating’) the pulsing width we can effectively control the light output from the LED, hence the term PWM or Pulse Width Modulation. Arduino also had PWM pins with a scale from 0 – 255 so we could have 255 brightness level on a LED.

This PWM image is from Arduino tutorial – credits: https://www.arduino.cc/en/tutorial/PWM

ESP32 / ESP8266 PWM example for one Channel

// Since someone asked about a modern AnalogWrite PWM example
// Just try to compile this one
include "Arduino.h"

// use first channel of 16 channels (started from zero)
define LEDC_CHANNEL_0 0
// use 13 bit precission for LEDC timer
define LEDC_TIMER_13_BIT 13
// use 5000 Hz as a LEDC base frequency
define LEDC_BASE_FREQ 5000
// fade LED PIN (replace with LED_BUILTIN constant for built-in LED)
define LED_PIN 25
bool brightDirection = 0;
int ledBright = 0;

void setup() {
  Serial.begin(115200);
  Serial.println("Hello PWM LED");
  // Setup timer and attach timer to a led pin
  ledcSetup(LEDC_CHANNEL_0, LEDC_BASE_FREQ, LEDC_TIMER_13_BIT);
  ledcAttachPin(LED_PIN, LEDC_CHANNEL_0);
}
// Arduino like analogWrite: value has to be between 0 and valueMax
void ledcAnalogWrite(uint8_t channel, uint32_t value, uint32_t valueMax = 255) {
  // calculate duty, 8191 from 2 ^ 13 - 1
  uint32_t duty = (8191 / valueMax) * min(value, valueMax);
  ledcWrite(channel, duty);
}

void loop() {
  // set the brightness on LEDC channel 0
  ledcAnalogWrite(LEDC_CHANNEL_0, ledBright);
  if (ledBright == 255 || ledBright == 0) {
    brightDirection = !brightDirection;
  }
  if (brightDirection) {
    ++ledBright;
  } else {
    --ledBright;
  }
  delay(15);
  Serial.println(ledBright);
}

The ESP32 has a PWM controller with 16 independent channels that can be configured to generate PWM signals with different properties. Just wanted to mention this possibility but I’m not going to extend myself in this topic since they are hundred of pages that explain it much better than I could do. Please check https://randomnerdtutorials.com/esp32-pwm-arduino-ide to have a nice PWM example.

Keep tuned and follow this blog to get more. In next chapter we are going to explore I2C communication and connect a thermometer to our ESP32 to display via Serial the room temperature.

PlatformIO: An alternative to Arduino IDE and a complete ecosystem for IoT

PlatformIO Logo

As an introduction I would like to make clear that I’m not a C++ advanced coder or IoT professional, I do this just because it’s a challenge, and because it’s a lot of fun compared to my 9 hrs/5 days a week web developer doing PHP and Admin panels for clients in Germany. Two months ago I started tinkering with SPI Cameras and the Espressif systems boards and that’s how this open source project was born. So far I was using Arduino since I do not need a super IDE, sometimes I also edit the code with vi or gedit instead of open a monster IDE that will eat your CPU alive. But gladly this is not the case. I was since long looking for a competitive alternative to Arduino when this github issue on the FS2 Camera Project called my interest:

tablatronix commented 8 days ago

I had to manually install this button library as it is not in platformio , is it in arduinos?

And that’s how after a few clicks I discovered Plaftormio.org that according to their home page it’s an open source IoT ecosystem. But what interested me more than this is the subtitle:  “Cross-platform IDE and unified debugger. Remote unit testing and firmware updates

So instead of answering tablatronix issue, I started installing this new IDE, that happened in a breeze.
1. First thing is to install the VS CODE Version. I choosed the Visual Studio code option since it has more features. Microsoft’s Visual Studio Code is the base and PlatformIO is built on the top of this.

2. Go to “Extensions” and install PlatformIO IDE “Development environment for IoT, Arduino, Espressif (ESP8266/ESP32)”

platformio IDE extensions is marked in RED just before PlatformIO logo

3. In my case since I used Arduino IDE before, go to PlatformIO alien face logo and select “Import project from Arduino”. Then select the folder where your Arduino project is and PlatformIO will create a Workspace for you with all the necessary structure.

4. Adjust serial monitor baud rate.  If you are using Espressif chips edit platformio.ini and add the following line at the end:

monitor_baud = 115200

This will make your serial work in the right baud rate for ESP8266 /ESP32 (Serial is the plug icon in the bottom just before the Terminal > icon)

5. FS Data. If you are using SPIFFS that in Arduino is the /data folder inside your sketch you will notice that in PlatformIO this folder needs to be at the root level. So you can simply move it one directory above. To upload SPIFFS data use the following command in the terminal:

pio run --target uploadfs
IMPORTANT: As difference with Arduino if you try to save a file in /1.JPG here you will get it saved on:
/spiffs/1.JPG so create this folder on /data or you will get; VFSFileImpl(): fopen(/spiffs/1.jpg) failed

6. Libraries in PlatformIO live inside a folder on your project called .piolibdeps Thanks god, they are not distributed on 3 different parts, like it happens with Arduino (Some in Arduino/libraries, some in Programs/Arduino/libraries and so on) but are there available for you in just one place :)
To install a new library is very easy, just go to PlatformIO.org/lib and type the name of the library to search. If found copy the resultant line in the Terminal just like point 5 and the IDE will look this up for you and download it using github to the  .piolibdeps folder.

pio lib install "WifiManager"

Sometimes you will need a library in a special branch and there is also an easy way to do this. Just use :

pio lib install <repository#tag> 

// Install development version of WifiManager library
pio lib install https://github.com/tzapu/WiFiManager.git#development

7. If you use Arduino before it’s possible that you used some of it’s constants. So if your sketch compiles, but it does not runs like expected try to add this include line at the beginning

#include <Arduino.h>
Including Arduino.h at the beginning of the sketch

As a footer note I must make clear that it takes some time to get accustomed to the new IDE. But it comes with a great benefit as it shows you much better C++ warnings, it’s prettier to use, and has the advantage that you can Ctrl+Click and navigate between different classes. Something that it was not possible to do with my old IDE. And the most beautiful update is that all libraries are in a single place per Project, like it should be, leaving you a clear idea of how much code and dependencies you are adding into your sketch.

In FS2 project porting it to the ESP8266 Wemos board this happened like a breeze. And it was just the fact of upgrading my code to use OneButton library. adding the include Arduino.h and that is. After uploading SPIFFS data and the new code, the camera was ready to be used. Now it’s not always that easy. trying to compile the same code to an Heltec ESP32 board, I got SPI communication issues with the camera and I’m still fighting with it.

UPDATE: I found what is going on here, and it’s that there are some problems with my sketch that uses I2C and wire library to comunicate with the Camera on the Heltec ESP32 environment. Error message is:
i2cCheckLineState(): Bus Invalid State, TwoWire() Can’t init. I solved it updating the platformio.ini configuration file to use:
board = lolin_d32
So using this board it compiles and works correctly. No idea why it does not using heltec_wifi_lora_32 I will have to research more.

Additional links of interest:

Source filter: src_filter
This option allows to specify which source files should be included/excluded from build process. It could be useful to keep the same core for ESP8266 and ESP32 but including different files to support both. So far I’ve been using 2 different branches something that is hard to maintain for obvious reasons.

Library dependencies: lib_deps declaration in platformio.ini
Like composer for PHP, this IDE offers a way to declarate your libs in the ini file. To check how a professional software for 3D-printing does take a look in Marlin configuration file. This is a very important point to keep in mind since after the lib_deps list is correctly added and tested, people testing your code just need to hit “build” to download them, saving a huge amount of time. This are FS2 library dependencies.

FS2 Camera project

If you are interested to build your own WiFi Camera for around 40€ of components and maybe 5€ of 3D-printed case, then check this project on github:

https://github.com/martinberlin/FS2

I’m giving out in december ten free 3D-printed cases, if you are interested on getting one and putting together a WIFi Camera please choose between Black PLA, black PETG or RED transparent and comment in this post. You can send me the address later per private message or in twitter. Thanks for your interest!