ENG-CANSAT-PICO-MISSION1-AUTONOMOUS

Introduction

Until now, we have worked with the emitter linked to a computer via USB cable.

Using the USB cable was very useful to capture the debugging message into the REPL Session.

We have two things to do:

• Start automatically your python script
• Making the CANSAT working autonomously

Start your Python script

If you want your script to start when powering up your Pico, just copy the script content into a file named main.py .

This approach is very efficient but can lead to plateform lock-up when the script is buggy or contains an infinite loop.

The aim is to check the status of a given pin (eg: GP22) before starting the user script (say user.py).

In case of trouble during testing/development we just switch-off the "RunApp" and press the reset button to restart the Pico.

Here is the content of main.py script.

from machine import Pin
run = Pin( 22, Pin.IN, Pin.PULL_UP )
if run.value() == 1:
    import user # load user.py file and execute it

To resume:

• If the RunApp switch is on the Run position at power-up the user.py script does start.
• If the RunApp switch is on the Stop position at power-up the user.py script will not start.

Power It

To work autonomously, the CanSat must be powered with a battery. This point have been adressed with a Adafruit PowerBoost 500 breakout board:

Crédit: AdaFruit Industries www.adafruit.com

The Adafruit PowerBoost 500 is a breakout board able:

• to discharge a Lipo battery to generates 5V output (500mA max)
• to charge the Lipo battery when connected to an external 5V supply
• to do the both operations at the same time.

The great thing about the PowerBoost is that it can use the Pico VBUS to recharge the Lipo. So, no need of an external power connexion to refill the Lipo (just plug you Pico to an USB Power source).

All of this have been adressed with great details in the Pico Powering section.

Pico Powering

How to properly power up your Pico

Cliquez ici

 

Sparing Power

The best approach to spare the energy is to consume the LiPo power as the last moment (to keept as must as power as possible for the launch).

There are several options for that:

1. Keeping the Pico Powered via USB as much as possible (with a computer or a powerbank).
2. Disabling the PowerBoost (and power down the complete projet):
   • WITHOUT Cansat Kit: Use a slide switch (or a jumper) to tie the PowerBoost EN to the GND
   • With Cansat Kit: The slide switch (or jumper) can be placed near of the border of the board.

Keeping the Pico Powered before launch have the advantage of having the software already running.
Powering-up at the last moment is also the risk of discovering an unespected issue (depending on how the setup have been tested).

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Written by Meurisse D. for MCHobby