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→MicroPython How To
This section of the tutoriel contains small portion of code explaining how to use digital pins, analog pins, buses and all the fundamentals to control the board with Python code.
This section of the tutoriel contains small portion of code explaining how to use digital pins, analog pins, buses and all the fundamentals to control the board with Python code.
Everything you learned about python language like variables, loops, conditionals, object programming, ... does applies to MicroPython.
Everything you learned about Python 3 language like variables, loops, conditionals, object programming, ... does applies to MicroPython.
A large part of standard Python libraries have been ported to MicroPython (partially or completely). Keep in mind that MicroControler doesn't have as much power and as much memory than a regular computer. So choice has been made: no gregorian calandar, no numpy (it exists some port anyway), no TKinter.
A large part of standard Python libraries have been ported to MicroPython (partially or completely). Keep in mind that MicroControler doesn't have as much power and as much memory than a regular computer. So choice has been made: no gregorian calandar, no numpy (it exists some port anyway), no TKinter.
Here some fundamentals about the Python language himself:
=== Needs some helps about python? ===
* [https://www.pythoncheatsheet.org/#Python-Basics www.Python'''Cheat'''Sheet.org] - Anyone can forget how to make loop, list, sclice, math operator...
[[Fichier:ENG-CANSAT-PICO-HowTo-Help-Me.png]]
This tutorial is not a training course about Python. Anyway, Python is quite easy to learn and do not requires lot of efforts.
Here follows some fundamentals help links about the Python language himself:
* [https://www.w3schools.com/python/ '''W3Schools''' on Python] : one of the best ressource for learning online (should I say "my favorite one).
* [https://www.pythoncheatsheet.org/#Python-Basics '''P'''ython'''C'''heat'''S'''heet.org] : Anyone can forget how to make loop, list, dictionary, tuple, list slice, math operator, generator...
* [https://www.pythonsheets.com/ pythonsheets.com] : more advanced cheat sheet.
== Print and Waits ==
== Print and Waits ==
Everything you will {{fname|print()}} will be sent to REPL (so over the USB-Serial line) and being visible in Thonny.
Everything you will {{fname|print()}} will be sent to REPL (so over the USB-Serial line) and being visible in Thonny.
This is incredibly useful to debug your software!
<syntaxhighlight lang="python">
<syntaxhighlight lang="python">
</syntaxhighlight>
</syntaxhighlight>
You can also sleep for milliseconds with {{fname|sleep_ms(x)}}
You can also sleep for milliseconds with {{fname|sleep_ms(x)}}.
[[Fichier:ENG-CANSAT-PICO-HowTo-print.png]]
== Control an output ==
== Control an output ==
That method returns a 16 bits value, so a number between 0 and 65535.
That method returns a 16 bits value, so a number between 0 and 65535.
{{ambox|text=Even if the {{fname|read_u16()}} returns a 16 bits values, the effective ADC resolution is still 12 bits. The MicroPython internal will just upscale the ADC value from 0..4095 to returned value 0..65535 by applying a multiplier.}}
{{ambox|text=Even if the {{fname|read_u16()}} returns a 16 bits values, the effective ADC resolution is still 12 bits. The MicroPython internal will just upscale the ADC value from 0..4095 to returned value 0..65535 by applying a multiplier.
The effective ADC reading precision is 3.3V/4095 = 0.000805V (0.8mv) }}
[[Fichier:ENG-CANSAT-FEATHER-PICO-HowTo-25.png]]
[[Fichier:ENG-CANSAT-FEATHER-PICO-HowTo-25.png]]
=== UART Bus ===
=== UART Bus ===
The onboard LED is tied to the GPIO 25. Here how to control it.
The UART is often compared to a serial port (which is in facts very similar to).
It allows to send and receives data from a device using the same interface like modem, GPS, terminal. UART/Serial ports are used to creates point to point communication.
When wiring an UART, the RX & TX connection must be cross-over like the wiring to GPS here below (see the [https://github.com/mchobby/esp8266-upy/tree/master/gps-ultimate gps-ultimate MicroPython library])
[[Fichier:ENG-CANSAT-PICO-HowTo-UART.png|480px]]
{{ambox|text=It is advised to use the UART(0) on GP0 & GP1. Indeed, UART(1) overlaps the SPI(0) used for Radio module. Alternative UART(1) position overlaps the I2C(0) bus. See the [[ENG-CANSAT-PICO-USER-GUIDE|Pinout]] for details.}}
<syntaxhighlight lang="python">
from machine import UART, Pin
# UART(0) on GP0 & GP1
uart = UART( 0, baudrate=9600)
# UART(1) on GP4 & GP5
uart = UART( 1, baudrate=9600, timeout=3000)
# Alternate position for UART(1) by using Bus Fabric feature
uart = UART( 1, rx=Pin(9), tx=Pin(8), baudrate=9600 )
</syntaxhighlight>
Outside of connecting device (like GPS) to the UART, you can also use an UART to get the REPL over it (exactly like USB connexion but over an UART. This may be kindly useful to bring a REPL connectivity over mobile network/device.
The following snip of code duplicates the REPL over the {{fname|UART(0)}} .
<syntaxhighlight lang="python">
<syntaxhighlight lang="python">
from machine import Pin
from machine import UART
from os import dupterm
uart = UART(0, baudrate=19200, bits=8, parity=None, stop=1)
os.dupterm( uart, 1 ) # Pico Firmware must be recompile with dupterm()
</syntaxhighlight>
</syntaxhighlight>
The {{fname|UART}} class is [https://docs.micropython.org/en/latest/library/machine.UART.html fully described into MicroPython documentation].
The {{fname|dupterm()}} function is [https://docs.micropython.org/en/latest/library/os.html#terminal-redirection-and-duplication described here into the MicroPython documentation].
{{underline|Tips & Tricks:}}
* One of the key parameter of UART is the {{fname|timeout}} parameter which indicates the timeout (in ms) to receive the end-of-line on {{fname|UART.readline()}} .
* See this [https://forums.raspberrypi.com/viewtopic.php?t=304410 Raspberry-Pi forum thread] to compile a dupterm() enabled firmware for Pico.
=== SPI Bus ===
=== SPI Bus ===
The onboard LED is tied to the GPIO 25. Here how to control it.
An SPI bus is high speed full duplex bus.
* High speed means several mega-hertz (can be up to +20 MHz).
* Full duplex means communicates in both direction at the same time.
Thanks to its high throughput, the SPI bus are used for display, data acquisition, data transmission, etc.
{{ambox|text=The Cansat RFM69 Radio module of Cansat kit do use {{fname|SPI(0)}} bus to exchange data with the MicroControler.}}
SPI bus are short (below 10cm) and uses '''3 wires for the data bus + a "Slave Select" wire per device''':
* MOSI: Master Out Slave In. Communication from the microcontroler to the device.
* MISO: Master In Slave Out. Communication from the device to the microcontroler.
* SCLK: Clock signal giving the rythme to the data transfer.
* SS: Slave Select (activated at LOW) used to activate the device on the bus. It is also used to start "transaction" with the device.
[[Fichier:ENG-CANSAT-PICO-HowTo-SPI.png]]
The following snip of code creates an instance of the {{fname|SPI(0)}} bus
<syntaxhighlight lang="python">
<syntaxhighlight lang="python">
from machine import Pin
from machine import Pin, SPI
ss = Pin( 5, Pin.OUT, value=1 ) # Slave Select in deactivated state by default.
# SPI(0) : GP4=Miso, GP5=/SS, GP6=Sck, GP7=Mosi
# reducing clock speed to 400 KHz
spi = SPI( 0, baudrate=400000 )
</syntaxhighlight>
</syntaxhighlight>
{{underline|Tips & Tricks:}}<br />Under MicroPython the SS pin is not "hardware" tied to a given SPI bus. User can freely choose any pin as "Slave Select" pin.
== Additional tutorials ==
== Additional tutorials ==