Introduction

Significant number of users asked about real time plotting examples in Python and tried to use matplotlib for it. Matplotlib is a great library, but its primary focus is offline data. For real time visualization tools like PyQT and Kivy work better. Here we will use pyqtgraph which is built on top of PyQT. Despite the fact that this example is only for Python for now, it shows the basic idea which remains the same across different programming languages and GUI frameworks.

Also, feel free to check Matthijs blog post about visualization in Julia.

Full code for this example can be found here.

Installing dependencies

All you need to install is BrainFlow and pyqtgraph.

python -m pip install -U brainflow
python -m pip install pyqtgraph==0.12.1

Or use requirements.txt file

pyqtgraph requires PyQT preinstalled, on unix like systems process of installation is different based on OS. On Fedora it’s as simple as:

sudo dnf install PyQt5

We recommend to use system package managers like dnf, apt, brew, etc instead installation using pip.

Real time plot using pyqtgraph

There are a lot of tutorials about pyqtgraph, we recommend this one.

Let’s copypaste code from it:

from PyQt5 import QtWidgets, QtCore
from pyqtgraph import PlotWidget, plot
import pyqtgraph as pg
import sys  # We need sys so that we can pass argv to QApplication
import os
from random import randint

class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        self.graphWidget = pg.PlotWidget()
        self.setCentralWidget(self.graphWidget)

        self.x = list(range(100))  # 100 time points
        self.y = [randint(0,100) for _ in range(100)]  # 100 data points

        self.graphWidget.setBackground('w')

        pen = pg.mkPen(color=(255, 0, 0))
        self.data_line =  self.graphWidget.plot(self.x, self.y, pen=pen)

        self.timer = QtCore.QTimer()
        self.timer.setInterval(50)
        self.timer.timeout.connect(self.update_plot_data)
        self.timer.start()

    def update_plot_data(self):
        self.x = self.x[1:]  # Remove the first y element.
        self.x.append(self.x[-1] + 1)  # Add a new value 1 higher than the last.

        self.y = self.y[1:]  # Remove the first
        self.y.append(randint(0,100))  # Add a new random value.

        self.data_line.setData(self.x, self.y)  # Update the data.


app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
w.show()
sys.exit(app.exec_())

Getting some data from BrainFlow

We will use brainflow_get_data.py from code samples as a starting point.

import argparse
import time
import numpy as np

import brainflow
from brainflow.board_shim import BoardShim, BrainFlowInputParams
from brainflow.data_filter import DataFilter, FilterTypes, AggOperations


def main():
    BoardShim.enable_dev_board_logger()

    parser = argparse.ArgumentParser()
    # use docs to check which parameters are required for specific board, e.g. for Cyton - set serial port
    parser.add_argument('--timeout', type=int, help='timeout for device discovery or connection', required=False,
                        default=0)
    parser.add_argument('--ip-port', type=int, help='ip port', required=False, default=0)
    parser.add_argument('--ip-protocol', type=int, help='ip protocol, check IpProtocolType enum', required=False,
                        default=0)
    parser.add_argument('--ip-address', type=str, help='ip address', required=False, default='')
    parser.add_argument('--serial-port', type=str, help='serial port', required=False, default='')
    parser.add_argument('--mac-address', type=str, help='mac address', required=False, default='')
    parser.add_argument('--other-info', type=str, help='other info', required=False, default='')
    parser.add_argument('--streamer-params', type=str, help='streamer params', required=False, default='')
    parser.add_argument('--serial-number', type=str, help='serial number', required=False, default='')
    parser.add_argument('--board-id', type=int, help='board id, check docs to get a list of supported boards',
                        required=True)
    parser.add_argument('--file', type=str, help='file', required=False, default='')
    args = parser.parse_args()

    params = BrainFlowInputParams()
    params.ip_port = args.ip_port
    params.serial_port = args.serial_port
    params.mac_address = args.mac_address
    params.other_info = args.other_info
    params.serial_number = args.serial_number
    params.ip_address = args.ip_address
    params.ip_protocol = args.ip_protocol
    params.timeout = args.timeout
    params.file = args.file

    board = BoardShim(args.board_id, params)
    board.prepare_session()

    # board.start_stream () # use this for default options
    board.start_stream(45000, args.streamer_params)
    time.sleep(10)
    # data = board.get_current_board_data (256) # get latest 256 packages or less, doesnt remove them from internal buffer
    data = board.get_board_data()  # get all data and remove it from internal buffer
    board.stop_stream()
    board.release_session()

    print(data)


if __name__ == "__main__":
    main()

Mixing it all together

We are one step away from this result.

We will not get data in the main function and in the main thread, but we want to prepare and release session there and pass board object to visualization class to access data. So, let’s patch our main function a little:

def main():
    BoardShim.enable_dev_board_logger()
    logging.basicConfig(level=logging.DEBUG)

    parser = argparse.ArgumentParser()
    # use docs to check which parameters are required for specific board, e.g. for Cyton - set serial port
    parser.add_argument('--timeout', type=int, help='timeout for device discovery or connection', required=False,
                        default=0)
    parser.add_argument('--ip-port', type=int, help='ip port', required=False, default=0)
    parser.add_argument('--ip-protocol', type=int, help='ip protocol, check IpProtocolType enum', required=False,
                        default=0)
    parser.add_argument('--ip-address', type=str, help='ip address', required=False, default='')
    parser.add_argument('--serial-port', type=str, help='serial port', required=False, default='')
    parser.add_argument('--mac-address', type=str, help='mac address', required=False, default='')
    parser.add_argument('--other-info', type=str, help='other info', required=False, default='')
    parser.add_argument('--streamer-params', type=str, help='streamer params', required=False, default='')
    parser.add_argument('--serial-number', type=str, help='serial number', required=False, default='')
    parser.add_argument('--board-id', type=int, help='board id, check docs to get a list of supported boards',
                        required=False, default=BoardIds.SYNTHETIC_BOARD)
    parser.add_argument('--file', type=str, help='file', required=False, default='')
    args = parser.parse_args()

    params = BrainFlowInputParams()
    params.ip_port = args.ip_port
    params.serial_port = args.serial_port
    params.mac_address = args.mac_address
    params.other_info = args.other_info
    params.serial_number = args.serial_number
    params.ip_address = args.ip_address
    params.ip_protocol = args.ip_protocol
    params.timeout = args.timeout
    params.file = args.file

    try:
        board_shim = BoardShim(args.board_id, params)
        board_shim.prepare_session()
        board_shim.start_stream(450000, args.streamer_params)
        g = Graph(board_shim)
    except BaseException as e:
        logging.warning('Exception', exc_info=True)
    finally:
        logging.info('End')
        if board_shim.is_prepared():
            logging.info('Releasing session')
            board_shim.release_session()

And patch our pyqtgraph part:

class Graph:
    def __init__(self, board_shim):
        self.board_id = board_shim.get_board_id()
        self.board_shim = board_shim
        self.exg_channels = BoardShim.get_exg_channels(self.board_id)
        self.sampling_rate = BoardShim.get_sampling_rate(self.board_id)
        self.update_speed_ms = 50
        self.window_size = 4
        self.num_points = self.window_size * self.sampling_rate

        self.app = QtGui.QApplication([])
        self.win = pg.GraphicsWindow(title='BrainFlow Plot',size=(800, 600))

        self._init_timeseries()

        timer = QtCore.QTimer()
        timer.timeout.connect(self.update)
        timer.start(self.update_speed_ms)
        QtGui.QApplication.instance().exec_()


    def _init_timeseries(self):
        self.plots = list()
        self.curves = list()
        for i in range(len(self.exg_channels)):
            p = self.win.addPlot(row=i,col=0)
            self.plots.append(p)
            curve = p.plot()
            self.curves.append(curve)

    def update(self):
        data = self.board_shim.get_current_board_data(self.num_points)
        avg_bands = [0, 0, 0, 0, 0]
        for count, channel in enumerate(self.exg_channels):
            # plot timeseries
            self.curves[count].setData(data[channel].tolist())

        self.app.processEvents()

Note: here we use get_current_board_data method which doesn’t remove data from the internal buffer. It allows you to implement sliding window using single method and wo any efforts

Finally, let’s add a title to our plot and some filters.

import argparse
import time
import logging
import random

import pyqtgraph as pg
from pyqtgraph.Qt import QtGui, QtCore

import brainflow
from brainflow.board_shim import BoardShim, BrainFlowInputParams, BoardIds, BrainFlowError
from brainflow.data_filter import DataFilter, FilterTypes, AggOperations, WindowFunctions, DetrendOperations


class Graph:
    def __init__(self, board_shim):
        self.board_id = board_shim.get_board_id()
        self.board_shim = board_shim
        self.exg_channels = BoardShim.get_exg_channels(self.board_id)
        self.sampling_rate = BoardShim.get_sampling_rate(self.board_id)
        self.update_speed_ms = 50
        self.window_size = 4
        self.num_points = self.window_size * self.sampling_rate

        self.app = QtGui.QApplication([])
        self.win = pg.GraphicsWindow(title='BrainFlow Plot',size=(800, 600))

        self._init_timeseries()

        timer = QtCore.QTimer()
        timer.timeout.connect(self.update)
        timer.start(self.update_speed_ms)
        QtGui.QApplication.instance().exec_()


    def _init_timeseries(self):
        self.plots = list()
        self.curves = list()
        for i in range(len(self.exg_channels)):
            p = self.win.addPlot(row=i,col=0)
            p.showAxis('left', False)
            p.setMenuEnabled('left', False)
            p.showAxis('bottom', False)
            p.setMenuEnabled('bottom', False)
            if i == 0:
                p.setTitle('TimeSeries Plot')
            self.plots.append(p)
            curve = p.plot()
            self.curves.append(curve)

    def update(self):
        data = self.board_shim.get_current_board_data(self.num_points)
        avg_bands = [0, 0, 0, 0, 0]
        for count, channel in enumerate(self.exg_channels):
            # plot timeseries
            DataFilter.detrend(data[channel], DetrendOperations.LINEAR.value)
            DataFilter.perform_bandpass(data[channel], self.sampling_rate, 51.0, 100.0, 2,
                                        FilterTypes.BUTTERWORTH.value, 0)
            DataFilter.perform_bandstop(data[channel], self.sampling_rate, 50.0, 4.0, 2,
                                        FilterTypes.BUTTERWORTH.value, 0)
            DataFilter.perform_bandstop(data[channel], self.sampling_rate, 60.0, 4.0, 2,
                                        FilterTypes.BUTTERWORTH.value, 0)
            self.curves[count].setData(data[channel].tolist())

        self.app.processEvents()


def main():
    BoardShim.enable_dev_board_logger()
    logging.basicConfig(level=logging.DEBUG)

    parser = argparse.ArgumentParser()
    # use docs to check which parameters are required for specific board, e.g. for Cyton - set serial port
    parser.add_argument('--timeout', type=int, help='timeout for device discovery or connection', required=False,
                        default=0)
    parser.add_argument('--ip-port', type=int, help='ip port', required=False, default=0)
    parser.add_argument('--ip-protocol', type=int, help='ip protocol, check IpProtocolType enum', required=False,
                        default=0)
    parser.add_argument('--ip-address', type=str, help='ip address', required=False, default='')
    parser.add_argument('--serial-port', type=str, help='serial port', required=False, default='')
    parser.add_argument('--mac-address', type=str, help='mac address', required=False, default='')
    parser.add_argument('--other-info', type=str, help='other info', required=False, default='')
    parser.add_argument('--streamer-params', type=str, help='streamer params', required=False, default='')
    parser.add_argument('--serial-number', type=str, help='serial number', required=False, default='')
    parser.add_argument('--board-id', type=int, help='board id, check docs to get a list of supported boards',
                        required=False, default=BoardIds.SYNTHETIC_BOARD)
    parser.add_argument('--file', type=str, help='file', required=False, default='')
    args = parser.parse_args()

    params = BrainFlowInputParams()
    params.ip_port = args.ip_port
    params.serial_port = args.serial_port
    params.mac_address = args.mac_address
    params.other_info = args.other_info
    params.serial_number = args.serial_number
    params.ip_address = args.ip_address
    params.ip_protocol = args.ip_protocol
    params.timeout = args.timeout
    params.file = args.file

    try:
        board_shim = BoardShim(args.board_id, params)
        board_shim.prepare_session()
        board_shim.start_stream(450000, args.streamer_params)
        g = Graph(board_shim)
    except BaseException as e:
        logging.warning('Exception', exc_info=True)
    finally:
        logging.info('End')
        if board_shim.is_prepared():
            logging.info('Releasing session')
            board_shim.release_session()


if __name__ == '__main__':
    main()