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ENG-CANSAT-PICO-MISSION1-CAPTURE (voir la source)

Version du 26 novembre 2022 à 14:43

11 787 octets ajoutés ,  26 novembre 2022 à 14:43
→‎Wire the radio module
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|-
 
|-
 
| MOSI
 
| MOSI
−
| GP7 (Miso)
+
| GP7 (Mosi)
 
|-
 
|-
 
| MISO
 
| MISO
−
| GP4 (Mosi)
+
| GP4 (Miso)
 
|-
 
|-
 
| SCK
 
| SCK
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The Pico pad on the board are large enough to quickly solder the TMP36 on the board. The TMP36 can also bee soldered under the board.
 
The Pico pad on the board are large enough to quickly solder the TMP36 on the board. The TMP36 can also bee soldered under the board.
   −
[[Fichier:ENG-CANSAT-PICO-TMP36-10.png|320px]]
+
[[Fichier:ENG-CANSAT-PICO-TMP36-10.png|560px]]
    
=== Wire the radio module ===
 
=== Wire the radio module ===
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Finally wire the RFM69HCW radio as follows
 
Finally wire the RFM69HCW radio as follows
   −
[[Fichier:ENG-CANSAT-PICO-RFM69HCW-to-Cansat-Pico-Base.jpg|640px]]
+
[[Fichier:ENG-CANSAT-PICO-RFM69HCW-to-Cansat-Pico-Base-fixed.jpg|640px]]
    
{| class="wikitable"  
 
{| class="wikitable"  
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| keep the same pin as receiver.<br />Otherwise use UEXT 10 (=gp10)
 
| keep the same pin as receiver.<br />Otherwise use UEXT 10 (=gp10)
 
|-
 
|-
−
| MOSI
+
| MISO
 
| 7
 
| 7
 
|  
 
|  
 
| GP4 = MISO
 
| GP4 = MISO
 
|-
 
|-
−
| MISO
+
| MOSI
 
| 8
 
| 8
 
|  
 
|  
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| PICO 3.3V
 
| PICO 3.3V
 
|}
 
|}
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== Download the code ==
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The code is available for download on the [https://github.com/mchobby/cansat-belgium-micropython GitHub associated to this wiki].
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{{download-box|Téléchargez Mission1 Cansat Emitter script (cansat.py)|https://github.com/mchobby/cansat-belgium-micropython/blob/main/mission1/cansat.py}}
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Without any comments, extra lines and print statement (used to debug), the script makes 33 lines long for the full fledged features.
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As showned in the following picture, the intermediate script testing runs for about 80.000 iterations and message sending without an issue.
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[[Fichier:ENG-CANSAT-PICO-MISSION1-CAPTURE-10.png]]
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== About testing ==
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Now, we will move forward in several steps.
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# Getting data from sensors + send them it over the REPL/Shell connection (to confirm good working) + transmit over radio
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# Testing the radio reception
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# Going autonomous + add the Lipo
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The code proposed here under has been tested up to 80000 iterations without issue, time when we decided to ends the test :-) .
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Once the script uploaded to your Pico, open the REPL/Shell over the USB-serial (with Thonny, Putty, MPRemote). The script can be started from REPL with {{fname|import cansat}} .
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You should see the following messages appears on the Serial Monitor.
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[[Fichier:ENG-CANSAT-PICO-MISSION1-CAPTURE-20.png]]
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Where we could see the transmitted messages with the iteration counter, timing and data.
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{{ambox|text=The '''ACK'''nowledgement feature is disabled to avoids unnecessary latency when waiting back for ACK response (which may never comes back in the case of a CanSat in high altitude). }}
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== Structuring the data ==
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The radio module only sends buffer of binary data to the receiver. This is a bit rough but efficient.
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So to transport the data to the receiver, we need to transform the values (float, integer) into their string representation.
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When having multiple data in their string representation is not enough, they must also been organized.
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'''The final format must be easy to parse and very compact''' (smaller is the radio message and higher is the chance for him to get to the ground without error).
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We propose the following format:
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<nowiki>:data1,data2,data3,data4;</nowiki>
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where:
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* ''':''' is the begin of data stream
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* ''';''' is the end of data stream
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* ''',''' is the separator between data items (like CSV format).
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* '''datax''' are the string representation of the various data. The characters ;:, are forbidden in this area.
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It is recommend to include the following:
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* '''counter''' as data1. {{fname|counter}} is a simple numeric variable incremented of one unit after each transmission. This would allow the receiver to detect lost message (since it would exist holes in the numbering of received messages).
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* '''time_sec''' as data2. This would help to create timing chart or time based data analysis. We suggest to use the {{fname|time.time()}} function which count the number of seconds since the last microcontroler reset.
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As explained later in the code the {{fname|msg}} variable contains the message to be transmitted to the ground. The python language offers facilities to format string and transform typed data to their string representation.
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<syntaxhighlight lang="python">
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msg = ":%i,%i,%6.2f,%5.2f,%5.2f;" % (counter,time.time()-ctime,hpa,temp,t)
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print( msg )
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# Send over RFM69HCW module
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rfm.send( bytes(msg , "utf-8") )
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</syntaxhighlight>
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The {{fname|":%i,%i,%6.2f,%5.2f,%5.2f;"}} string formating use {{fname|%i}} to format an integer and {{fname|%6.2f}} or {{fname|%5.2f}} to format floating point value. The parameter to be formatted are given with the tuple (having 5 entries) just being the {{fname|%}} sign.
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As the {{fname|rfm.send()}} only acept {{fname|bytes}}/binary data, the {{fname|msg}} is transformed into an array of bytes with {{fname|bytes()}} . {{fname|bytes()}} array can only contains ASCII bytes < 127, any other character/byte must be appropriately encoded! This is why the call to {{fname|bytes(msg , "utf-8")}} mentions the source string encoding (which is [https://fr.wikipedia.org/wiki/UTF-8 UTF-8] nowadays).
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== LEDs and Error management ==
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Being able to understand rapidly what's happening inside your object is essential to rapidly fix the issue.
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The best is to figure out what's happening is to use LED, blink status, heartbeat.
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By doing so, no need to attach an USB cable and opens a terminal over the USB-Serial to figure out the status of the object.
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[[Fichier:ENG-CANSAT-PICO-MISSION1-CAPTURE-25.png|360px]]
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The [https://github.com/mchobby/cansat-belgium-micropython/tree/main/mission1 cansat2.py] script do re-enforce error controls with {{fname|try...except}} statements in the script and showing various onboard LED patterns in case of error.
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Error Code are reported as quick serie of blink following by slow blink... counting the slow blink gives the error code number.
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{| class="wikitable" border="1"
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|-
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| align="center" | LED operation
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| align="center" | Description
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| align="center" | Fix the issue
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|- style="font-size: 90%"
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| align="left" | OFF (continuously)
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| align="left" | No code is running/started.
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| align="left" | Check that cansat code is called/executed from main.
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|- style="font-size: 90%"
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| align="left" | Short blink
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| align="left" | The radio is emitting data.
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| align="left" | The software is running properly and emitting data.
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|- style="font-size: 90%"
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| align="left" | Error 1
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| align="left" | RFM69 Radio module initialisation error
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| align="left" | Double check the RFM69 wiring.<br />Check wiring vs pins declaration (in code)
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|- style="font-size: 90%"
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| align="left" | Error 2
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| align="left" | BMP280 initialisation error
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| align="left" | Double check the BMP280 wiring.
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|- style="font-size: 90%"
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| align="left" | Error 3
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| align="left" | BMP280 read data error.
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| align="left" | Double check stability of I2C bus.
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|- style="font-size: 90%"
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| align="left" | Error 4
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| align="left" | Main application loop crash unexpectedly
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| align="left" | Check error description description in the REPL console.
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|}
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== The code explained ==
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Here some explanation about the {{fname|cansat.py}} script used in the CanSat.
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This MicroPython script would:
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* Initialize the buses and hardware
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* Collect the sensor data
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* Send it over the USB-serial connection
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* Send it over the radio link
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First, the script will includes all the needed libraries.
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<syntaxhighlight lang="python">from machine import SPI, I2C, Pin, ADC
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from rfm69 import RFM69
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from bme280 import BME280, BMP280_I2CADDR
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import time
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</syntaxhighlight>
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This section is immediately followed by the various CONSTANT used in the script.
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<syntaxhighlight lang="python">FREQ          = 433.1
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ENCRYPTION_KEY = b"\x01\x02\x03\x04\x05\x06\x07\x08\x01\x02\x03\x04\x05\x06\x07\x08"
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NODE_ID        = 120 # ID of this node
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BASESTATION_ID = 100 # ID of the node (base station) to be contacted
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</syntaxhighlight>
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{{dbox-orange|Don't forget to update the radio frequency '''FREQ''' and the '''ENCRYPTION_KEY''' encryption key. }}
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=== Creating ressources ===
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Then we create the needed buses resources to access the various sensor.
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<syntaxhighlight lang="python">spi = SPI(0, baudrate=50000, polarity=0, phase=0, firstbit=SPI.MSB)
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nss = Pin( 5, Pin.OUT, value=True )
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rst = Pin( 3, Pin.OUT, value=False )
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i2c = I2C(0)
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</syntaxhighlight>
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Next we create the RFM69 radio object (named {{fname|rfm}}) and the BMP280 radio object (named {{fname|bmp}}).
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<syntaxhighlight lang="python"># RFM Module
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rfm = RFM69( spi=spi, nss=nss, reset=rst )
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rfm.frequency_mhz  = FREQ
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rfm.encryption_key = ( ENCRYPTION_KEY )
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rfm.node          = NODE_ID # This instance is the node 120
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rfm.destination    = BASESTATION_ID # Send to specific node 100
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# BMP280 (uses the BME280)
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bmp = BME280( i2c=i2c, address=BMP280_I2CADDR )
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</syntaxhighlight>
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At the end of initialization section, we do creates the instances for the analog reading (the TMP36, named {{fname|adc}}) and LED controling (named {{fname|led}}).
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<syntaxhighlight lang="python"># TMP36 analog pin
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adc = ADC(Pin(26))
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# Onboard LED
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led = Pin(25, Pin.OUT)
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</syntaxhighlight>
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=== Information logging ===
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Just before the main loop, the script print the essential data.
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<syntaxhighlight lang="python"># Main Loop
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print( 'Frequency    :', rfm.frequency_mhz )
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print( 'encryption    :', rfm.encryption_key )
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print( 'NODE_ID      :', NODE_ID )
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print( 'BASESTATION_ID:', BASESTATION_ID )
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print( '***HEADER***' )
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print( ":iteration_count,time_sec,pressure_hpa,tmp36_temp,bmp280_temp;" )
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print( '***DATA***' )
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</syntaxhighlight>
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=== Main Loop execution ===
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The main loop is composed of an infinite {{fname|while}} loop.
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<syntaxhighlight lang="python"># Iteration counter
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counter = 1
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# ctime contains the time (in seconds) when the script was stared
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ctime = time.time() # Now
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while True:
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    # Main Loop body
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    ...
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    ...
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    ...
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    counter += 1    # increment iteration counter
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    time.sleep(0.4) # wait 0.4 second between iterations
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</syntaxhighlight>
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The '''Mainloop body''' executes the following steps:
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# Reading the sensors data
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# Preparing the message
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# Sending message
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## Switch on the onboard LED
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## Log message
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## Send message
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## Turn of the LED
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{{underline|'''Reading sensor data:'''}}
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Reading the BMP280 sensor data relies on the {{fname|bme280.py} library previously detailled.
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Reading the temperature from TMP36 relies on analog reading and some conversion calculation.
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<syntaxhighlight lang="python"># read BMP280
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t,hpa,rh =  bmp.raw_values # Temp, press_hPa, humidity
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# Read tmp36 (analog)
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value = adc.read_u16()
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mv = 3300.0 * value / 65535
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temp = (mv-500)/10
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</syntaxhighlight>
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Next the mainloop do prepare the string message (variable {{fname|msg}} by using the powerful Python string formatting feature.
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{{underline|'''Formatting data:'''}}
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This can be done with one single line. Notice the expression {{fname|time.time()-ctime}} calculating the elapse time (in second) since the mainloop started. 
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<syntaxhighlight lang="python"># message: iteration_count,time_sec,pressure_hpa,tmp36_temp,bmp280_temp (coma separated)
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msg = ":%i,%i,%6.2f,%5.2f,%5.2f;" % (counter,time.time()-ctime,hpa,temp,t)
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</syntaxhighlight>
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{{underline|'''Sending data:'''}}
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The onboard LED is switched on during data transmission (and print). This makes the LED flashing briefly while data us transmitted.
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The data packet are sent without ACK, this would avoids unnecessary latency by waiting for ACK. Indeed, the Cansat will not modifies its behaviours if the data are not received on the ground station.
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<syntaxhighlight lang="python">led.on() # Led ON while sending data
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print( msg )
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# Send a packet without ACK - Send it, don't care if it is received or not
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rfm.send(bytes(msg , "utf-8") )
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led.off()
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</syntaxhighlight>
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Just to remind, the {{fname|rfm.send()}} only accepts binary data as generated with bytes() or bytearray(). The message string must be converted to a binary with {{fname|bytes()}}. As binary data does not accept value > 127 without a proper encoding then the bytes() conversion must identifies the encoding of the source string to applies the adequate encoding scheme (UTF8 -> Binary).
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== Fault tolerant design ==
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The goal is to transmit the data to the ground station.<br />The code of the Cansat Emitter (this section) and Receiver BaseStation (next section) are doing the job.
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However, what would happens to your data if the antenna did break? All the data are lots!
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This is where the "[[ENG-CANSAT-PICO-LOG|Data Logging]]" would be a great help!
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As showed earlier, it is also possible to store/save the data into the MicroPython FileSystem (the Flash).
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A good approach would be:
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# to save the data in the file
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# then send it over Radio.
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In this way, the data stays available inside the CanSat and could be readed as suited.
    
{{ENG-CANSAT-PICO-TRAILER}}
 
{{ENG-CANSAT-PICO-TRAILER}}
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