LEDAndNeopixels < IoT_Course

Lecture 2: LEDs and NeoPixel

CSC 321: Embedded Sysytem

First Semeter 2020/2021

The ESP32-WROVER-B MCU

Slide 1 of 32

CPU Pinout

Please note: The pin numbers IOxx on the ESP32 correspond to the GPIO pin numbers

Datasheet: https:// www.espressif.com /sites/default/files/documentation/esp32-wrover-b_datasheet_en.pdf

Slide 2 of 32

Meaning of pins on ESP32

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How to program the processor

	Several development tools are available: ESP_IDF: The official Espressif development tool. Includes a gcc compiler for the ESP8266 and the ESP32 Please see: https://docs.espressif.com/projects/esp-idf/en/latest The Arduino IDE Needs extensions for these processors and the different CPU boards see: https://docs.espressif.com/projects/esp-idf/en/latest MicroPython see: https://micropython-docs-esp32.readthedocs.io/en/esp32_doc

Several development tools are available:

ESP_IDF: The official Espressif development tool.
Includes a gcc compiler for the ESP8266 and the ESP32

Please see:
https://docs.espressif.com/projects/esp-idf/en/latest

The Arduino IDE
Needs extensions for these processors
and the different CPU boards

see:

https://docs.espressif.com/projects/esp-idf/en/latest

MicroPython

see:
https://micropython-docs-esp32.readthedocs.io/en/esp32_doc

Slide 4 of 32

Flashing the code

Slide 5 of 32

esptool

esptool is called from the Makefiles in ESP-IDF
esptool is used when we upload code from the Arduino IDE to the processor flash
esptool is used with Micropython IDE on uPyCraft/Thonny

installs Micropython onto the processor flash

In the above cases the use of esptool is hidden to us.

We can however also execute esptool directly.

Slide 6 of 32

How to write a Micropython program?

First we need a Micropython interpreter!

You find the sources here:

https://github.com/micropython/micropython/

In the repository you find ports for the ESP8266 and the ESP32.

In order to compile the code you need the ESP-IDF and its cross compilers

The code compiles into a binary file (firmware-combined.bin) which contains a boot loader and the interpreter.

This binary must be uploaded and flashed.

For documentation of the ESP32port of Micropython look at

http://docs.micropython.org/en/latest/esp32/tutorial/intro.html

Slide 7 of 32

How to communicate with the Micropython interpreter?

We use a serial connection passing through the micro USB connection.

As soon as we connect the processor card to the PC we see the serial port to connect for communication

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What is REPL?

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The communication tools: minicom

You see the command prompt and you can interact with Micropython.

But … how to upload scripts?

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The command line tool ampy

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IDE for Micropython: uPyCraft

Slide 12 of 32

Slide 13 of 32

Thonny

Slide 14 of 32

Thonny

Thonny is a complete Integrate Development Environment (IDE)

which lets you

Access the REPL
Create directories on the Micropython file system
Upload scripts
Syntax check scripts
Run scripts
Install Micropython on your processor board

Slide 15 of 32

Thonny

Thonny is an IDE for Python which has provisions for Micropython.

Under Tools → Options button you can select the type of

Python interpreter you intend to use.

Slide 16 of 32

Flashing Micropython

Compiling a new version of Micropython is substantially much easier with Thonny.

You still need to install esptool first. You just select your port and firmware then install.

Slide 17 of 32

!IoT Hello World program

A “Hello World” program, just printing “Hello World” on the screen

does not look very exciting.

However, this is generally used to verify that the infrastructure

Compiler, linker, downloader, flash program

are working correctly

In embedded systems printing can be quite complex

and a blinking LED is used instead.

Slide 18 of 32

Switching on and off a LED

The ESP32-WROVER-B have a “user LED” connected to GPIO 19.

How do we control this LED?

Define that the LED is connected to GPIO 19
Program this pin as output
Write a logic 1 to the pin to switch it on
Write a logic 0 to the pin to switch it off
The logic state may be inverted if the LED is active low

Slide 19 of 32

Micropython hardware functions

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The machine.Pin class

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Switch the LED on, version 1

Slide 22 of 32

Switch the LED on, version 2

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The blinking LED

Now we put the code into a script and run it

Slide 24 of 32

Changing the light intensity

The LED is connected to a digital line which can only be set to 0 or Vcc.

How can we change the light intensity and dim the LED?

The light intensity depends on the average current flowing through the LED.

The answer is PWM: pulse width modulation.

Slide 25 of 32

PWM in Micropython

Slide 26 of 32

Our PWM implementation

Slide 27 of 32

The WS2812B LED

A more complex LED:

rgb LED used in LED chains.
each ws18b12 contains the 3 colored LEDs and a controller.
Can be cascaded and individually addressed, depending on its position in the chain
Needs precise timing
To use it we pass through the neopixel library built into micropython

Slide 28 of 32

!WS2812B timing

For all the details on the ws2812b look at

https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf

24 bit of colour data puts 2e24 colours at your disposal

Coding of a single bit

The control word:

Slide 29 of 32

Cascading the WS2812B

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Using the neopixel library

Slide 31 of 32

… and our code

We have a single neopixel connected to

GPIO pin 4 (ESP8266)

GPIO pin 21 (ESP32)

This code works on both CPUs!

Slide 32 of 32

-- Isaac Armah-Mensah - 2021-02-28

Comments

I	Attachment	History	Action	Size	Date	Who
png	MPY1.png	r1	manage	423.0 K	2021-03-02 - 08:20	IsaacArmahMensah
jpg	esp32board.jpg	r1	manage	279.8 K	2021-03-02 - 00:20	IsaacArmahMensah
png	esp32board.png	r1	manage	2095.9 K	2021-02-28 - 01:28	IsaacArmahMensah
png	esptool.png	r2 r1	manage	385.0 K	2021-02-28 - 16:01	IsaacArmahMensah
png	interpret.png	r1	manage	105.0 K	2021-03-02 - 00:42	IsaacArmahMensah

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Topic revision: r5 - 2021-03-02 - IsaacArmahMensah