Air Rocket Logger

This is some simple code to log data from an air rocket.

Components

All components are bought from Pimoroni

• Pico LiPo (16MB)
• ICM20948 Motion Sensor Breakout
• JST-SH Cable (male to male), any length is fine
• LiPo Battery (150mA)
• Any USB-C cable, for loading the code and accessing the data

Assembly

1. If you haven't already, install CircuitPython on your Pico, by dragging and dropping the .uf2 file onto the drive named RPI-RP2. The drive should disappear, then re-mount under the new name CIRCUITPY. You'll need v8.2.9 to run, which the previous link should download.
   • If the RPI-RP2 drive does not show up at first, press and hold the BOOT button on the Pico, and double press the POWER button while still holding. Once the drive shows up, you can let go of BOOT.
2. Use the JST cable to connect the Pico and the motion sensor
3. Copy and paste the whole libs/, code.py, and boot.py from this repository to the Pico's drive, ideally in that order.
4. Unplug the Pico from your computer, and plug in the battery to the slot on the Pico
5. If the white LED does not come on, quickly press the POWER button on the Pico once
6. Allow the Pico to log some data for 10+ seconds
7. Remove the battery, and plug the Pico back into your computer. The data should be stored in data.csv, which you should copy to a different location on your machine

Important Notes

• data.csv is appended to every time the Pico runs, and will print a new header line every time this occurs. Be careful you're only using the dataset you want to use
• Sometimes the Pico won't boot up properly, I have no idea why. It seems to happen both on battery, and when plugging into the computer, and is easily fixed by just pressing the POWER button. If the white light isn't on, data won't be logged, and it won't show up as a drive on your computer
• Data is read from the motion sensor as quick as it can (up to 20 times per second), and written to data.csv every 5 seconds, to make sure it doesn't get stuck. It's important to wait at least 5s after you've collected your useful data, to make sure it's all written to the log.
• In testing, the median time between readings was around 0.142s, although this occasionally has a spike of up to 0.5s when writing data to the flash. This spike can be reduced by modifying the timeout on line 20 in code.py from 5 to a higher value, although this will also affect how long you have to wait before depowering the Pico. See the chart below for experimental results.

Modifying the Code

By default, the Pico will be configured such that the code itself can write to its flash, which causes it to be mounted as a read-only file system when you plug it into a computer. To change the code (or to delete data.csv), unplug the Pico from your computer, and use a jumper cable or bit of wire to short pin 0 to any ground connection (there's one labelled "-" two pins away). Keep this connection shorted when you plug it back into your computer, and the Pico should mount itself in writeable mode. No data can be written to the log file while the Pico is in this mode.

Libraries

Libraries in the libs/ directory are from Adafruit's CircuitPython Bundle, and are redistributed for convenience of install. The most up-to-date versions can be found in their original repository.