Basic Test

Before we get to plotting various system status parameters, let's use a stand alone test to make sure all the essential software pieces are working. We'll also use this example as a way to explain how the code works. If you wanted to adapt this to plot something else, this would be a good starting point.

Here's the code:

import time
from collections import deque
import random
import math
# Blinka CircuitPython
import board
import digitalio
import adafruit_rgb_display.ili9341 as ili9341
# Matplotlib
import matplotlib.pyplot as plt
# Python Imaging Library
from PIL import Image

#pylint: disable=bad-continuation
#==| User Config |========================================================
REFRESH_RATE = 0.5
HIST_SIZE = 61
PLOT_CONFIG = (
    #--------------------
    # PLOT 1 (upper plot)
    #--------------------
    {
    'line_config' : (
        {'color' : '#FF0000', 'width' : 2, 'style' : '--'},
        { },
        )
    },
    #--------------------
    # PLOT 2 (lower plot)
    #--------------------
    {
    'title' : 'sin()',
    'ylim' : (-1.5, 1.5),
    'line_config' : (
        {'color' : '#00FF00', 'width' : 4},
        )
    }
)

def update_data():
    ''' Do whatever to update your data here. General form is:
           y_data[plot][line].append(new_data_point)
    '''
    # upper plot data
    for data in y_data[0]:
        data.append(random.random())

    # lower plot data
    y_data[1][0].append(math.sin(0.5 * time.monotonic()))

#==| User Config |========================================================
#pylint: enable=bad-continuation

# Setup X data storage
x_time = [x * REFRESH_RATE for x in range(HIST_SIZE)]
x_time.reverse()

# Setup Y data storage
y_data = [ [deque([None] * HIST_SIZE, maxlen=HIST_SIZE) for _ in plot['line_config']]
           for plot in PLOT_CONFIG
         ]

# Setup display
disp = ili9341.ILI9341(board.SPI(), baudrate = 24000000,
                       cs  = digitalio.DigitalInOut(board.D4),
                       dc  = digitalio.DigitalInOut(board.D5),
                       rst = digitalio.DigitalInOut(board.D6))

# Setup plot figure
plt.style.use('dark_background')
fig, ax = plt.subplots(2, 1, figsize=(disp.width / 100, disp.height / 100))

# Setup plot axis
ax[0].xaxis.set_ticklabels([])
for plot, a in enumerate(ax):
    # add grid to all plots
    a.grid(True, linestyle=':')
    # limit and invert x time axis
    a.set_xlim(min(x_time), max(x_time))
    a.invert_xaxis()
    # custom settings
    if 'title' in PLOT_CONFIG[plot]:
        a.set_title(PLOT_CONFIG[plot]['title'], position=(0.5, 0.8))
    if 'ylim' in PLOT_CONFIG[plot]:
        a.set_ylim(PLOT_CONFIG[plot]['ylim'])

# Setup plot lines
#pylint: disable=redefined-outer-name
plot_lines = []
for plot, config in enumerate(PLOT_CONFIG):
    lines = []
    for index, line_config in enumerate(config['line_config']):
        # create line
        line, = ax[plot].plot(x_time, y_data[plot][index])
        # custom settings
        if 'color' in line_config:
            line.set_color(line_config['color'])
        if 'width' in line_config:
            line.set_linewidth(line_config['width'])
        if 'style' in line_config:
            line.set_linestyle(line_config['style'])
        # add line to list
        lines.append(line)
    plot_lines.append(lines)

def update_plot():
    # update lines with latest data
    for plot, lines in enumerate(plot_lines):
        for index, line in enumerate(lines):
            line.set_ydata(y_data[plot][index])
        # autoscale if not specified
        if 'ylim' not in PLOT_CONFIG[plot].keys():
            ax[plot].relim()
            ax[plot].autoscale_view()
    # draw the plots
    canvas = plt.get_current_fig_manager().canvas
    plt.tight_layout()
    canvas.draw()
    # transfer into PIL image and display
    image = Image.frombytes('RGB', canvas.get_width_height(),
                            canvas.tostring_rgb())
    disp.image(image)

print("looping")
while True:
    update_data()
    update_plot()
    time.sleep(REFRESH_RATE)

And then to run it do the following. If you've already set the BLINKA_FT232H environment variable, you don't need to do that again.

Make sure you've set the BLINKA_FT232H environment variable so Blinka knows to look for the FT232H on the USB bus!
Download: file
$ export BLINKA_FT232H=1
$ python3 tft_sidekick_basic.py

You should get something like this on the display.

The top plot is two lines of random numbers. The bottom line is a sine curve. In the next section we'll go through this code and talk about how it works.

This guide was first published on Nov 13, 2019. It was last updated on Nov 13, 2019. This page (Basic Test) was last updated on Dec 06, 2019.