Session 2: Micropython and
Hardware access
Uli Raich
Formally CERN, Geneva, Switzerland
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Slide 1 of 35
The WeMos D1 mini CPU card
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ESP8266 cost: 2.21 Euros |
ESP32 cost: 4.1o Euros |
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Slide 2 of 35
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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
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Slide 3 of 35
CPU pinouts for reference
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Slide 4 of 35
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 |
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Slide 5 of 35
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Slide 6 of 35
How to program the processor
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Slide 7 of 35
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Slide 8 of 35
- 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 when the Micropython IDE 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.
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Slide 9 of 35
How to write a Micropython program?
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Slide 10 of 35
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?
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Slide 11 of 35
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Slide 12 of 35
The communication tools: minicom
You see the command prompt and you can interact with Micropython.
But … how to upload scripts?
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Slide 13 of 35
The command line tool ampy
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Slide 14 of 35
IDE for Micropython: uPyCraft
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Slide 15 of 35
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
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Slide 16 of 35
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.
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Slide 17 of 35
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
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
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Slide 18 of 35
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Slide 19 of 35
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.
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Slide 20 of 35
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.
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Slide 21 of 35
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
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Slide 22 of 35
Micropython hardware functions
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Slide 23 of 35
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Slide 24 of 35
Switch the LED on, version 1
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Slide 25 of 35
Switch the LED on, version 2
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Slide 26 of 35
Now we put the code into a script and run it
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Slide 27 of 35
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.
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Slide 28 of 35
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Slide 29 of 35
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Slide 30 of 35
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
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Slide 31 of 35
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Slide 32 of 35
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Slide 33 of 35
Using the neopixel library
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Slide 34 of 35
We have a single neopixel connected to
GPIO pin 4 (ESP8266)
or
GPIO pin 21 (ESP32)
This code works on both CPUs!
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Slide 35 of 35
Uli Raich - 2019-05-13
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