01_Blink.md

LED Blink - The ESP-Arduino Hello World (01_Blink)

This is a traditional Hello World sample for the ESP8266 board and Arduino framework. The sample turns on/off a LED using a GPIO pin and prints the famous Hello World!.

Objectives

• Learn to use PlatformIO.
• Understand the basic program structure.
• Learn how to connect ESP8266 and how to upload a program (flash).
• Learn how to use GPIO pins to drive a LED.

Hardware

First lets connect the hardware...

Connections of ESP8266 pins:

• RST of ESP8266 connected via a push switch to LOW.
  • When the button gets pressed it will restart our program (and the chip).
• EN is connected to HIGH to enable the chip.
  • The chip enters sleep mode if connected to LOW (or not connected at all).
  • Sleep mode is used to lower the power consumption.
• GND and 3V3 is connected to GND and voltage 3.3V respectively.

The sample program will blink a LED. The LED's cathode (shorter leg) is connected to GND and the anode is connected via a 220Ω resistor to the GPIO pin #13. The resistor is needed to limit the current on the LED (not to burn it).

Software

The structure of the project files comes from the Platform IO. The underlying programming language is C++. The most interesting part of the sample is located in the main program file src\Main.cpp:

// reference the arduino framework
#include <Arduino.h>

// the LED's GPIO pin number
#define LED 13

void setup()
{
  // initialize serial communication
  Serial.begin(115200);

  Serial.println("");
  Serial.println("Hello World!");
  Serial.println("");

  // initialize LED digital pin as an output.
  pinMode(LED, OUTPUT);
}

void loop()
{
  // turn the LED on (HIGH is the voltage level)
  digitalWrite(LED, HIGH);
  // wait for a second
  delay(1000);
  // turn the LED off by making the voltage LOW
  digitalWrite(LED, LOW);
   // wait for a second
  delay(1000);
}

The name of the main file can be whatever you like, but it needs to have a meaningful C++ extension (e.g. .cpp or .c) and has to be located under src folder.

Some explanation on the code...

Any program should have exactly one setup() and loop() functions defined. The setup() is executed only once - when the chip starts (when powered or reset); after that loop() is executed repeatedly.

The #include <Arduino.h> brings in all the Arduino framework functions.

The Serial enables us to send (and recieve) some characters into the Serial Monitor. This is useful to output diagnostic information to debug our program.

Lets run the program:

• Compile using PlatformIO
• Put the ESP into UART Boatloader mode
  • Set GPIO0 to PullDown
  • Press RESET button briefly
• Upload program using PlatformIO
• Open Serial Monitor in PlatformIO
• Set GPIO0 to loose (or PullUp)
• Press RESET button briefly

When all is successful the LED will blink and the output from the Serial Monitor will have the Hello World! line:

Arduino Reference

• pinMode(pin, mode)
• digitalWrite(pin, value)
• delay(ms)
• setup()
• loop()
• Serial.begin()
• Serial.print()

Worth reading (at home)

• Diode and LED Polarity
• Serial Reference

Exercise

1. Connect the hardware parts and upload the program to ESP.
   • Connect the USB-TTL converter.
   • Open the 01_blink project in PlatformIO.
   • Build / Upload (ensure ESP is in upload mode).
2. Modify the program to make the LED emit SOS signal (...---...)

• Change & upload the program.

3. Blink 3 LEDs one after another

• Connect 2 more LEDs (green and yellow) to GPIO pins #16 and #12.
• Change and upload the program.