ESP32

ESP32 Diagram

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ESP32 Capacity

- WiFi 2.4Ghz	- Analog GPIO
- Bluetooth	- Touch sensor
- 240Mhz dual core	- Hall sensor
- Digital GPIO	- I2C, SPI, SD, UART,...

GPIOs digital specificities

GPIO	INPUT	OUTPUT	Comments
0	Y	Y	Pullup auto
1	N	Y	TX0 UART PC
2	Y	Y	Pulldown auto
3	Y	N	RX0 UART PC
4 - 5	Y	Y
6 - 11	N	N	internal flash
12	Y	Y	Pulldown auto
13 - 14	Y	Y
15	Y	Y	Pullup auto
16 - 33	Y	Y
34 - 39	Y	N	No pullup/pulldown
EN	N	N	ESP32 Reset

Structure

// Initialization function
void setup() {}

// Run function 
void loop() {}

Digital IO

pinMode(pin, [INPUT, OUTPUT, INPUT_PULLDOWN, INPUT_PULLUP]);
int digitalRead(pin);
digitalWrite(pin, value);

value can be HIGH or LOW

Analog IO

// return value between 0 - 4095
int analogRead(pin);

// return value in millivolts
int analogReadMilliVolts(pin);

// fake analog => PWM; 0 - 255
analogWrite(pin, value);

Advanced IO

// generate square wave at freq
tone(pin, freq, duration_ms?);
// stop generating wave
noTone(pin);

// shift each bit of value to dataPin at clkPin speed
// if value = 22 (0010110) and bitOrder MSBFIRST then
// dataPin will take value 0, 0, 1, 0, 1, 1, 0 at rhythm
// of clkPin
shiftOut(dataPin, clkPin, [MSBFIRST, LSBFIRST], value);

Time

unsingned long millis(); // overflow: 50days
unsigned long micros(); // overflow 70min
delay(ms);
vTaskDelay(ms); // use if multi-threading
delayMicroseconds(us)

Serial

void setup() {
  Serial.begin(baudrate); // usually 115200
}

void loop() {
  if (Serial.available() == 0) {
    String message = Serial.readString();
    // can be read byte by byte with Serial.read();
    message.trim();
  }
  Serial.print("Hello");
  Serial.println(" World");
  // Not mandatory, wait for transmission finish
  Serial.flush();
}

External interrupts

attachInterrupt(pin, function, [LOW, CHANGE, RISING, FALLING]);
detachInterrupt(pin);
noInterrupts(); // disable all interruptions
interrupts(); // re-enable all interruptions

Mutli threading

/!\ do not overload core 0, this core control WiFi

// core: 0 or 1
TaskHandle_t taskRef;
xTaskCreatePinnedToCore(taskFunc, threadName, stackSize, 
                        parameters, priority, &taskRef, core);
vTaskDelete(taskRef);

// example :
TaskHandle_t myThreadTask;
xTaskCreatePinnedToCore(myThread, "My thread", 10000, 
                        NULL, 2, &myThreadTask, 0);

void myThread(void* parameter) {
    doSomething();
    vTaskDelay(200);
    doSomethingElse();
    vTaskDelete(myThreadTask);
}

WIFI

Connect to wifi AP

#include <WiFi.h>
#define SSID zenika
#define PWD zenika

void setup() {
  Serial.begin(115200);
  WiFi.begin(SSID, PWD);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
  Serial.print("Connected. IP: ");
  Serial.println(WiFi.localIP());
}

HTTP

HTTP Client request with HTTPClient lib

#include <HTTPClient.h>
String serverUrl = "http://192.168.0.88:3000/ping";

void setup() {
  // WiFi connection [...]
}

void loop() {
  if(myConditionToSendRequest) {
    HTTPClient http;
    String serverPath = serverUrl + "?name=Zenika";
    http.begin(serverPath);
    int httpResponseCode = http.GET();
    if (httpResponseCode > 0) {
      Serial.print("HTTP Response code: ");
      Serial.println(httpResponseCode);
      String response = http.getString();
      Serial.println(response);
    } else {
      Serial.print("Error code: ");
      Serial.println(httpResponseCode);
    }
    // Free resources
    http.end();
  }
}

Web server

#include <WebServer.h>

WebServer server(3000);

void handlePingRequest() {
  server.send(200, "text/html", "OK");
  digitalWrite(LED_BUILTIN, HIGH);
  delay(1000);
  digitalWrite(LED_BUILTIN, LOW);
}

void setup() {
  // WiFi connection [...]
  server.on("/ping", handlePingRequest);
  server.begin();
}

void loop() {
  server.handleClient();
}

Note that server.handleClient(); is mandatory to tell the lib to check network stack request buffer.

Otherwise, request from clients will not be accept.

The longer the delay between handleClient the longer the request connection will take.