Accelerometer data collection on a MicroBit

[Lightning42]

Hi there.

This is my first forum post here so bear with me until I get the ropes. I am looking to use the accelerometer on the MicroBit to measure the velocity of a rocket I will be launching at a medium PSI. I have figured out how to display where it is tilting, but I have no clue how the accelerometer measures these things and how it can save data. Essentially, what I'm asking is, is there any way I can collect the data from the accelerometer in a file which I can then copy and use for analysis? If so, how can I do this and what are the units that it measures in?

Thank you for your time!

[jimmo]

Hi,

The accelerometer returns values on each axis between -1024 and 1024, which correspond to an actual experienced acceleration of -2 to 2 g. i.e. you would expect an micro:bit sitting flat on the table to return approximately 1g (i.e. 512) in one axis, and 0 on the other two axes. More info here: https://microbit-micropython.readthedoc ... meter.html

On the micro:bit, you can access the filesystem using the standard Python APIs.

Code: Select all

f = open('path.txt', 'w')
f.write('hello\n')

So something like this would return 10 seconds of data to a CSV file for 10 seconds after pressing the A button.

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from microbit import *
# Wait for button to be pressed to start recording.
while not button_a.was_pressed():
  pass
with open('data.csv', 'w') as f:
  for i in range(1000):
    f.write('{},{},{},{}\n'.format(running_time(),accelerometer.get_x(), accelerometer.get_y(), accelerometer.get_z())
    sleep(10)

To access the files later, I recommend using Mu (https://codewith.mu/) Note that the filesystme on the micro:bit is unrelated to the USB drive that appears when you plug it into your computer -- that's only for updating the firmware. (This is different to other MicroPython boards such as Pyboard).

[rcolistete]

There is also :
MicroFS - A simple command line tool and module for interacting with the limited file system provided by MicroPython on the BBC micro:bit.

Mu Editor is simpler to use, but in some Linux distributions it is a lot harder to install (PyQt dependencies issues, etc).

[Syu]

Hi,

I also want to make the similar accelerometer data logger made of micro:bit, so I use two micro:bits, radio techniques, serial communication by MicroPython cording. But, measuring in a few minutes, suddenly the serial communication stops and the logger does not work.
The error message is : ERROR: not enough values to unpack (expected 2, got 1)


I refer to this page. I'm lucky to find this page. If possible, I would like to use the serial data, for example, measured every five seconds in a day.
Finally I want to use that data in csv file.
Is there any way to get such a data log?


I’m no good at using English and I'm a beginner about programs and one-board computer so I need long time to write and read the messages.

Any help will be appreciated.

[lujo]

Hi,

I'm also using two micro:bits for data collection. One micro:bit generates data, sends the data to a second micro:bit. The second micro:bit sends the data to a computer. Copied from a minimal working setup:

The micro:bit data sender:

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radio.config(group=17, power=5)
radio.on()

while True:
    radio.send(str(accelerometer.get_x()))
    sleep(500)

The micro:bit data receiver:

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radio.config(group=17, power=5)
radio.on()

while radio.receive():
    pass

while True:
    data = radio.receive()
    if data:
        print(data)   # sends data to computer
        display.set_pixel(2,2,9)
        sleep(50)
        display.set_pixel(2,2,0)

Writing collected data to a file:

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#!/usr/bin/python3

import serial
import time

port = "/dev/ttyACM0"
ser = serial.Serial(port=port, baudrate=115200, timeout=1)

while ser.read():
  pass

with open('microbit.dat', 'a') as f:
  while True:
    try:
      data = ser.readline().strip().decode("ascii")
      if data:
        print(int(time.time()), data, file=f, flush=True)
    except:
      pass

lujo

[jimmo]

suddenly the serial communication stops and the logger does not work.
The error message is : ERROR: not enough values to unpack (expected 2, got 1)

My guess is that this error is stopping your program.

The error is likely caused by something like

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x, y = something()

Maybe you have something like:

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x, y = msg.split(' ')

But if msg doesn't split into two things, then you'll get that error.

The important thing with the radio is that sometimes messages can get corrupted and your program needs to be able to handle that. So something like

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parts = msg.split(' ')
if len(parts) == 2:
  # valid message
  x, y = parts

[Syu]

Thanks for your replies!!

I'll use the programs and review my program.
I have not realized that sometimes messages can get corrupted...

[Anders_Fg]

This is how I use one microbit to collect data.
I make a new file with a random name and can then move the file to a computer.
Press A for start reading and B for stop reading.
----

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from microbit import *
from random import random
tal = str(random())
f = open(tal + '.txt','w')
f.write("  x       y        z \n")
def skriva_fil():
    while True:
        x=str(accelerometer.get_x())
        y=str(accelerometer.get_y())
        z=str(accelerometer.get_z())
        f.write(x +"    "+ y + "     " + z + '\n')
        if button_b.is_pressed():
            f.close()
            break
        sleep(1000)
while True:
    if button_a.is_pressed():
        skriva_fil()

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