4. Data Logging vscode

4.1. References for data logging

1. For byte decoding to a string see: https://docs.python.org/3/library/stdtypes.html#bytes.decode

2. For microbit uart see: https://microbit-micropython.readthedocs.io/en/v2-docs/uart.html

---

4.2. Microbit code

The uart (universal asynchronous receiver-transmitter) module lets you talk to a device connected to your board using a serial interface.

Below is sample code to stream the accelerometer values to the serial port.

This is for a microbit attached to a computer which will receive the data.

from microbit import *

    def send_data():
        x = accelerometer.get_x()
        y = accelerometer.get_y()
        z = accelerometer.get_z()
        acc_str = str(x) + ',' + str(y) + ',' + str(z)
        uart.write(acc_str)
        uart.write('\n')

    uart.init(9600)
    sending = False
    while True:
        if button_a.was_pressed():
            sending = True
        if button_b.was_pressed():
            sending = False
        if sending:
            send_data()
        sleep(100)

Button pressing is used to control the sending of data.

Press A to send data.

Press B to stop sending data.

In the code above, the accelerometer data is sent.

---

4.3. VScode

The code below collects data from the microbit, saves it to a csv file and plots it.

Adjust data_count = 20 to the number of data points desired.

Adjust sleep_ms = 100 to the time in milli-sec between readings. Make sure that it is not shorter than the sleep between sends on the microbit.

Adjust ser.port = ‘COM3’ to match the serial port that is used when the microbit is attached. It is usually ‘COM3’.

Adjust filename = 'microbit_data.csv' to suit.

import serial
import time
import csv
import matplotlib.pyplot as plt

data_count = 20
sleep_ms = 100
# Set up the Serial connection to capture the Microbit communications
ser = serial.Serial()
ser.baudrate = 9600
ser.port = 'COM3'
ser.open()

data = []
# Loop until count reaches data_count
count = 0
while True:
    # Read in a line from the Microbit, decode the bytes string to a string
    microbitreaddata = ser.readline().decode('utf-8')
    # remove "\n" -- end of line from each line if present.
    data.append(microbitreaddata.rstrip())
    # print to terminal if wanted
    time.sleep(sleep_ms / 1000)
    count += 1
    if count > data_count:
        break

# Close the serial connection
ser.close()

# convert lists of stings to lists of ints
data_list = []
for line in data:
    line_list = line.split(",")
    str_to_int = list(map(int, line_list))
    data_list.append(str_to_int)

# save to csv

my_headers = ['time','x','y', 'z']
filename = 'microbit_data.csv'
with open(filename, 'w', newline='') as my_file:
    writer = csv.writer(my_file)
    writer.writerow(my_headers)
    writer.writerows(data_list)

# convert data to 4 lists
# [[21075, 36, 96, -1020]...]
times = []
x_vals = []
y_vals = []
z_vals = []
for sublist in data_list:
    times.append(sublist[0])
    x_vals.append(sublist[1])
    y_vals.append(sublist[2])
    z_vals.append(sublist[3])

xAxis = times
plt.grid(True)
plt.xlabel('times')
plt.ylabel('acc')
plt.title('acc v time')

## LINE GRAPH ##
plt.plot(xAxis, x_vals, color='red', marker='x', label = "x_vals")
plt.plot(xAxis, y_vals, color='blue', marker='o', label = "y_vals")
plt.plot(xAxis, z_vals, color='green', marker='*', label = "z_vals")

# format dates so they are angled to fit
plt.gcf().autofmt_xdate()
plt.legend()
plt.show()