Slide 1: Setting up and IoT

Session 2: Micropython and

Hardware access

Uli Raich

Formally CERN, Geneva, Switzerland

Slide 2: The WeMos D1 mini CPU card

ESP8266 cost: 2.21 Euros	ESP32 cost: 4.1o Euros

Slide 3: CPU Pinout

ESP8266	ESP32

to the GPIO pin numbers

The pins in the white fields go to the WeMos D1 mini bus

and are also available on the ESP8266

The other pins are only accessible on the ESP32 CPU card

The pin numbers Dx do not correspond to GPIO pin numbers!

Please refer to the next slide for correspondence

Slide 4: CPU pinouts for reference

Slide 5: Meaning of pins on ESP8266

GPIO: General Purpose Input Output. Drives a single digital line which can be programmed input or output SCL/SDA: The I2C bus:a 2 wire bus interfacing sensors or actuators to the CPU SCL,MISO,MOSI,SS: SPI the Serial Peripheral Interface. Used fast communication with external device

Slide 6: Meaning of pins on ESP32

Slide 7: How to program the processor

Flashing the code

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

We can however also execute esptool directly.

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 ESP8266 port of Micropython look at

https://docs.micropython.org/en/latest/esp8266/tutorial/index.html

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

UART bridge and a new device: dev/ttyUSB0 is created.

This device is used to communicate with the Micropython REPL.

You see the command prompt and you can interact with Micropython. But … how to upload scripts?

What is REPL?

The communication tools: minicom

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

But … how to upload scripts?

The command line tool ampy

IDE for Micropython: uPyCraft

uPyCraft

uPyCraft is a rather 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

Flashing Micropython

This has already been done for you! However, it is easy if you want to do it

at home with a new processor board.

Compiling a new version of Micropython is substantially harder but also perfectly possible.

uPyCraft(2)

uPyCraft is based on QT4 and is available for Linux, Windows and Mac.

It is written in PyQt4 the Python language binding to Qt4.

I tried to correct as much as I could to make the PyQt5 version usable on Linux:

https://github.com/uraich/uPyCraft-Qt5

Thonny

Thonny (2)

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.

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.

Switching on and off a LED

The ESP8266 and the ESP32 have a “user LED” connected to GPIO 2.

How do we control this LED?

• Define that the LED is connected to GPIO 2
  
  
• 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

Micropython hardware functions

The machine.Pin class

Switch the LED on, version 1

Switch the LED on, version 2

The blinking LED

Now we put the code into a script and run it

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.

PWM in Micropython

Our PWM implementation

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
  
  

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:

Using the neopixel library

… and our code

We have a single neopixel connected to

GPIO pin 4 (ESP8266)

or

GPIO pin 21 (ESP32)

This code works on both CPUs!

The I2C bus

I2C stands for Inter-Integrated-Circuit. It was invented by Philips Semiconductor

in 1982. Slow, short distance.

Quite a number of sensors in the "WeMos D1 sensor shield collection use the I2C bus

• SHT30 temperature and humidity sensor
• DS1307 real time clock
• The BMP180 barometric pressure and temperature sensor
  
  
• The SSD1306 OLED (Organic Light Emitting Diode) display

The physical bus

The CPU (master) connects to the sensors (slaves) through

2 digital lines:

• SCL: the clock
• SDA: the data

I2C start and stop sequence

When the master want to talk to the slave it issues a start sequence

It terminates the transfer with a stop sequence

I2C addressing

When talking to a slave the master sends a seven bit address

followed by a read/write bit

This allows to access at most 128 devices

I2C data transfer

Data is transmitted 8 bits at a time followed by an acknowledge bit.

If acknowledge is low, transfer ok, otherwise: send stop sequence

I2C write cycle

• Send start sequence
• Send I2C address and R/W bit low
• Send internal register number
• Send data byte
• Optionally send further data bytes
• Send stop sequence

I2C read cycle

• Send start sequence
• Send slave address with R/W low
• Send address of internal register
• Send a start sequence again
• Send slave address with R/W high
• Read data byte
• Send stop sequence

I2C in Micropython

Scanning the I2C bus

The SHT30 digital temperature and relative humidity sensor

data sheet

A look at the SHT30 driver

https://afnog.iotworkshop.africa/pub/AFNOG/HardwareAccessAndMicropython/sht30.py.txt

Reading out the SHT30

Results from the SHT30

Where to find the demo code

While for the course we only use the CPU and 2 sensor shields:

• ESP8266 CPU (a more powerful ESP32 CPU exists)
• SHT30 temperature and humidity sensor

https://github.com/uraich/MicroPython_IoTDemos

WeMos D1 mini sensor and actuator shields (1)

Pushbutton	WS2812 cascadable rgb LED	SSD1306 OLED display
DS118B20 temperature sensor	DHT11 temperature and relative humidity sensor	8x8 LED Matrix

Wemos D1 mini sensor and actuator shields (2)

Passive Buzzer	Data Logger	SHT30 temperature and humidity sensor
triple base		my prototype board: LED + photo resistor

Cost

Pinouts of shields

Documentation for the demo programs

Demo programs for all the shields are available on github:

https://github.com/uraich/MicroPython_IoTDemos

A short description of every program can be found in the README

The data logger

The data logger features a DS1307 Real Time Clock (RTC) backed up by a battery An SD card socket also provided. This allows to store large amounts of data locally The RTC keeps the time and measurements can be supplied with a time tag Programs to set and read the RTC are provided. One of the programs setting the RTC gets the time from and NTP server such that manual specification of the current date and time are not needed.

https://github.com/uraich/MicroPython_IoTDemos/tree/master/drivers/ds1307

The push button shield

DS18B20 shield

SSD1306 48x64 OLED display

This one is also an I2C device

It provides 48*64 pixels and allows to

• Write a few characters of text
• Do simple graphics

framebuf class included in Micropython such that all

drawing methods of the framebuf are available for drawing:

https://docs.micropython.org/en/latest/library/framebuf.html

For an example see:

https://github.com/uraich/MicroPython_IoTDemos/tree/master/drivers/oled

The DHT11 shield

	The DHT11 is a digital temperature and relative humidity sensor. It uses a proprietary protocol of communication with its controlling host implemented in the dht.DHT11 class

The LED matrix

The LED matrix has 8x8 LEDs on it, which can individually be switched on or off. In addition to the mled class which takes care of the communication between the host and the device and which has classes to clear the display, set a pixel on or off and to change the brightness, I wrote a class matrix which takes a number 0..64 and lights this number of LEDs starting from bottom left

The buzzer

This shield implements a passive buzzer. A passive buzzer takes a frequency(an active buzzer takes a signal level) and produces a sound at this frequency. This means that the frequency can be changed and a tune can be played. In https://github.com/uraich/MicroPython_IoTDemos/tree/master/drivers/buzzer you will find a program interpreting songs on RTTTL (Ring Tone Text Transfer Language) and playing these on the buzzer A small song library is also provided

The prototype module

This is a home build module featuring a photo-resistor measuring the light intensity impinging on it. It provides an analogue value converted to digital by the ADC on the WeMos D1 CPU Please note that the ESP8266 has a single 10 bit ADC while the ESP32 has 3 12 bit ADCs. A MUX provides up to 18 analogue channels The light intensity can be changed with an LED

The triple base

This module allows to easily stack a rather larger number of shields to a sandwich.

Make sure however that the GPIO lines used by the modules do not clash

Exercises

Now it is up to

You

to do the work!

The exercises are here:

https://afnog.iotworkshop.africa/do/view/AFNOG/Session2

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Uli Raich - 2019-05-13

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