Setting up and IoT

Session 2: Micropython and

Hardware access

Uli Raich

Formally CERN, Geneva, Switzerland

Slide 1 of 64

The WeMos D1 mini CPU card

ESP8266

cost: 2.21 Euros

ESP32

cost: 4.1o Euros

Slide 2 of 64

CPU Pinout


ESP8266	ESP32

Please note: The pin numbers IOxx on the ESP32 correspond

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 3 of 64

CPU pinouts for reference

Slide 4 of 64

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

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 5 of 64

Meaning of pins on ESP32

Slide 6 of 64

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 7 of 64

Flashing the code

Slide 8 of 64

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

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 9 of 64

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

Slide 10 of 64

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?

Slide 11 of 64

What is REPL?

Slide 12 of 64

The communication tools: minicom

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

But … how to upload scripts?

Slide 13 of 64

The command line tool ampy

Slide 14 of 64

IDE for Micropython: uPyCraft

Slide 15 of 64

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

Slide 16 of 64

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.

Slide 17 of 64

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.

The Linux version did not work for me when running Ubuntu 18.04 or later.

I found a version based on PyQt5 (new version of QT) which was even worse.

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

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

Slide 18 of 64

Thonny

Slide 19 of 64

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.

Slide 20 of 64

!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 21 of 64

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

Slide 22 of 64

Micropython hardware functions

Slide 23 of 64

The machine.Pin class

Slide 24 of 64

Switch the LED on, version 1

Slide 25 of 64

Switch the LED on, version 2

Slide 26 of 64

The blinking LED

Now we put the code into a script and run it

Slide 27 of 64

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 28 of 64

PWM in Micropython

Slide 29 of 64

Our PWM implementation

Slide 30 of 64

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 31 of 64

!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 32 of 64

Cascading the WS2812B

Slide 33 of 64

Using the neopixel library

Slide 34 of 64

… 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 35 of 64

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

Slide 36 of 64

The physical bus

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

2 digital lines:

SCL: the clock
SDA: the data

Slide 37 of 64

!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

Slide 38 of 64

!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

Slide 39 of 64

!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

Slide 40 of 64

!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

Slide 41 of 64

!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

Slide 42 of 64

!I2C in Micropython

Slide 43 of 64

Scanning the I2C bus

Slide 44 of 64

The SHT30 digital temperature and relative humidity sensor

The SHT30 is a digital temperature and humidity sensor based on the I2C bus

Here is its data sheet.

Temperature precision: +- 0.3 °C

Relative humidity: +- 3 %

Works on 2.4V – 5.5 V

Slide 45 of 64

A look at the SHT30 driver

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

Slide 46 of 64

Reading out the SHT30

Slide 47 of 64

Results from the SHT30

Slide 48 of 64

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
Ws2812B rgb LED (neopixel) there are many more available on the market.

We have a dozen such shields here for demo.

All demo programs can be found at:

https://github.com/uraich/MicroPython_IoTDemos

Slide 49 of 64

!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

Slide 50 of 64

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

Slide 51 of 64

Cost

Slide 52 of 64

Pinouts of shields

Slide 53 of 64

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

Slide 54 of 64

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.

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

Slide 55 of 64

The push button shield

Slide 56 of 64

!DS18B20 shield

Slide 57 of 64

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

The ssd1306 class inherits from the

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

Slide 58 of 64

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

Slide 59 of 64

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 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

Slide 60 of 64

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

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

Slide 61 of 64

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

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

Slide 62 of 64

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

Slide 63 of 64

Exercises

Now it is up to

You

to do the work!

The exercises are here:

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

Slide 64 of 64

Uli Raich - 2019-05-13

Comments

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png	lsusb.png	r1	manage	73.3 K	2019-05-14 - 11:48	UliRaich
png	minicom.png	r1	manage	17.2 K	2019-05-14 - 11:42	UliRaich
png	neopixel.png	r1	manage	165.5 K	2019-05-14 - 12:46	UliRaich
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png	protoBoard.png	r1	manage	882.8 K	2019-05-14 - 15:13	UliRaich
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png	pwm.png	r1	manage	51.4 K	2019-05-14 - 12:27	UliRaich
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png	tripleBase.png	r1	manage	196.1 K	2019-05-14 - 15:11	UliRaich
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png	wemosButton.png	r1	manage	113.3 K	2019-05-14 - 14:55	UliRaich
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png	wemosSHT30.png	r1	manage	102.9 K	2019-05-14 - 15:11	UliRaich
png	wemosWS2812.png	r1	manage	144.2 K	2019-05-14 - 14:55	UliRaich
png	ws2812Bits.png	r1	manage	11.9 K	2019-05-14 - 12:42	UliRaich
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png	ws2812ControlWord.png	r1	manage	7.6 K	2019-05-14 - 12:42	UliRaich

This topic: AFNOG > WebHome > AFNOGWorkshop2019 > AFNOG-2019Slides > WorkshopSlides > HardwareAccessAndMicropython
Topic revision: r7 - 2019-06-11 - UliRaich

Session 2: Micropython andHardware accessUli RaichFormally CERN, Geneva, Switzerland

Now it is up to

You

to do the work!

Comments

Session 2: Micropython and

Hardware access

Uli Raich

Formally CERN, Geneva, Switzerland