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ENG-CANSAT-PICO-MISSION1-CAPTURE (voir la source)
Version du 26 novembre 2022 à 14:43
, 26 novembre 2022 à 14:43→Wire the radio module
|-
|-
| MOSI
| MOSI
| GP7 (Miso)
| GP7 (Mosi)
|-
|-
| MISO
| MISO
| GP4 (Mosi)
| GP4 (Miso)
|-
|-
| SCK
| SCK
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"
| 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
|
|
The code is available for download on the [https://github.com/mchobby/cansat-belgium-micropython GitHub associated to this wiki].
The code is available for download on the [https://github.com/mchobby/cansat-belgium-micropython GitHub associated to this wiki].
{{download-box|Téléchargez Mission1 Cansat Emitter script (cansat.py)|https://raw.githubusercontent.com/mchobby/cansat-belgium/master/mission1/cansat.py}}
{{download-box|Téléchargez Mission1 Cansat Emitter script (cansat.py)|https://github.com/mchobby/cansat-belgium-micropython/blob/main/mission1/cansat.py}}
Without any comments, extra lines and print statement (used to debug), the script makes 33 lines long for the full fledged features.
Without any comments, extra lines and print statement (used to debug), the script makes 33 lines long for the full fledged features.
* '''datax''' are the string representation of the various data. The characters ;:, are forbidden in this area.
* '''datax''' are the string representation of the various data. The characters ;:, are forbidden in this area.
It is recommend to include the following:
* '''counter''' as data1. packetnum is a simple variable increment 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).
* '''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).
* '''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.
* '''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.
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.
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.
As the {{fname|rfm.send()}} only send bytes, the {{fname|msg}} is transformed into an array of bytes with {{bytes()}} . {{bytes()}} array can only contains ASCII < 127, any other character must be appropriately encoded! This is why the call to {{fname|bytes(msg , "utf-8")}} mentions the source string encoding (wich is [https://fr.wikipedia.org/wiki/UTF-8 UTF-8] nowadays).
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).
== LEDs and Error management ==
Being able to understand rapidly what's happening inside your object is essential to rapidly fix the issue.
The best is to figure out what's happening is to use LED, blink status, heartbeat.
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.
[[Fichier:ENG-CANSAT-PICO-MISSION1-CAPTURE-25.png|360px]]
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.
Error Code are reported as quick serie of blink following by slow blink... counting the slow blink gives the error code number.
{| class="wikitable" border="1"
|-
| align="center" | LED operation
| align="center" | Description
| align="center" | Fix the issue
|- style="font-size: 90%"
| align="left" | OFF (continuously)
| align="left" | No code is running/started.
| align="left" | Check that cansat code is called/executed from main.
|- style="font-size: 90%"
| align="left" | Short blink
| align="left" | The radio is emitting data.
| align="left" | The software is running properly and emitting data.
|- style="font-size: 90%"
| align="left" | Error 1
| align="left" | RFM69 Radio module initialisation error
| align="left" | Double check the RFM69 wiring.<br />Check wiring vs pins declaration (in code)
|- style="font-size: 90%"
| align="left" | Error 2
| align="left" | BMP280 initialisation error
| align="left" | Double check the BMP280 wiring.
|- style="font-size: 90%"
| align="left" | Error 3
| align="left" | BMP280 read data error.
| align="left" | Double check stability of I2C bus.
|- style="font-size: 90%"
| align="left" | Error 4
| align="left" | Main application loop crash unexpectedly
| align="left" | Check error description description in the REPL console.
|}
== The code explained ==
Here some explanation about the {{fname|cansat.py}} script used in the CanSat.
This MicroPython script would:
* Initialize the buses and hardware
* Collect the sensor data
* Send it over the USB-serial connection
* Send it over the radio link
First, the script will includes all the needed libraries.
<syntaxhighlight lang="python">from machine import SPI, I2C, Pin, ADC
from rfm69 import RFM69
from bme280 import BME280, BMP280_I2CADDR
import time
</syntaxhighlight>
This section is immediately followed by the various CONSTANT used in the script.
<syntaxhighlight lang="python">FREQ = 433.1
ENCRYPTION_KEY = b"\x01\x02\x03\x04\x05\x06\x07\x08\x01\x02\x03\x04\x05\x06\x07\x08"
NODE_ID = 120 # ID of this node
BASESTATION_ID = 100 # ID of the node (base station) to be contacted
</syntaxhighlight>
{{dbox-orange|Don't forget to update the radio frequency '''FREQ''' and the '''ENCRYPTION_KEY''' encryption key. }}
=== Creating ressources ===
Then we create the needed buses resources to access the various sensor.
<syntaxhighlight lang="python">spi = SPI(0, baudrate=50000, polarity=0, phase=0, firstbit=SPI.MSB)
nss = Pin( 5, Pin.OUT, value=True )
rst = Pin( 3, Pin.OUT, value=False )
i2c = I2C(0)
</syntaxhighlight>
Next we create the RFM69 radio object (named {{fname|rfm}}) and the BMP280 radio object (named {{fname|bmp}}).
<syntaxhighlight lang="python"># RFM Module
rfm = RFM69( spi=spi, nss=nss, reset=rst )
rfm.frequency_mhz = FREQ
rfm.encryption_key = ( ENCRYPTION_KEY )
rfm.node = NODE_ID # This instance is the node 120
rfm.destination = BASESTATION_ID # Send to specific node 100
# BMP280 (uses the BME280)
bmp = BME280( i2c=i2c, address=BMP280_I2CADDR )
</syntaxhighlight>
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}}).
<syntaxhighlight lang="python"># TMP36 analog pin
adc = ADC(Pin(26))
# Onboard LED
led = Pin(25, Pin.OUT)
</syntaxhighlight>
=== Information logging ===
Just before the main loop, the script print the essential data.
<syntaxhighlight lang="python"># Main Loop
print( 'Frequency :', rfm.frequency_mhz )
print( 'encryption :', rfm.encryption_key )
print( 'NODE_ID :', NODE_ID )
print( 'BASESTATION_ID:', BASESTATION_ID )
print( '***HEADER***' )
print( ":iteration_count,time_sec,pressure_hpa,tmp36_temp,bmp280_temp;" )
print( '***DATA***' )
</syntaxhighlight>
=== Main Loop execution ===
The main loop is composed of an infinite {{fname|while}} loop.
<syntaxhighlight lang="python"># Iteration counter
counter = 1
# ctime contains the time (in seconds) when the script was stared
ctime = time.time() # Now
while True:
# Main Loop body
...
...
...
counter += 1 # increment iteration counter
time.sleep(0.4) # wait 0.4 second between iterations
</syntaxhighlight>
The '''Mainloop body''' executes the following steps:
# Reading the sensors data
# Preparing the message
# Sending message
## Switch on the onboard LED
## Log message
## Send message
## Turn of the LED
{{underline|'''Reading sensor data:'''}}
Reading the BMP280 sensor data relies on the {{fname|bme280.py} library previously detailled.
Reading the temperature from TMP36 relies on analog reading and some conversion calculation.
<syntaxhighlight lang="python"># read BMP280
t,hpa,rh = bmp.raw_values # Temp, press_hPa, humidity
# Read tmp36 (analog)
value = adc.read_u16()
mv = 3300.0 * value / 65535
temp = (mv-500)/10
</syntaxhighlight>
Next the mainloop do prepare the string message (variable {{fname|msg}} by using the powerful Python string formatting feature.
{{underline|'''Formatting data:'''}}
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.
<syntaxhighlight lang="python"># message: iteration_count,time_sec,pressure_hpa,tmp36_temp,bmp280_temp (coma separated)
msg = ":%i,%i,%6.2f,%5.2f,%5.2f;" % (counter,time.time()-ctime,hpa,temp,t)
</syntaxhighlight>
{{underline|'''Sending data:'''}}
The onboard LED is switched on during data transmission (and print). This makes the LED flashing briefly while data us transmitted.
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.
<syntaxhighlight lang="python">led.on() # Led ON while sending data
print( msg )
# Send a packet without ACK - Send it, don't care if it is received or not
rfm.send(bytes(msg , "utf-8") )
led.off()
</syntaxhighlight>
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).
== Fault tolerant design ==
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.
However, what would happens to your data if the antenna did break? All the data are lots!
This is where the "[[ENG-CANSAT-PICO-LOG|Data Logging]]" would be a great help!
As showed earlier, it is also possible to store/save the data into the MicroPython FileSystem (the Flash).
A good approach would be:
# to save the data in the file
# then send it over Radio.
In this way, the data stays available inside the CanSat and could be readed as suited.
{{ENG-CANSAT-PICO-TRAILER}}
{{ENG-CANSAT-PICO-TRAILER}}