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example-display-python.rst

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Display Example (Python)

In this tutorial, we'll display different things on the Modulo display based on which button is pressed.

We'll look at two different ways to accomplish this, with polling and events.

Hardware required:

  • Modulo Base (or Modulo Particle Base)
  • Controller Modulo (or Particle Photon)
  • Display Modulo

Polling

The following example uses polling to constantly check the state of the buttons and draw different things. It's the simplest way to get the job done.

Save this code to a file called "display.py", then from a terminal run "python display.py". Press Ctrl+C to stop the program.

# Import the modulo python library
import modulo

# Create a new Port object using the first Modulo Controller it finds.
port = modulo.Port()

# Create a Display object attached to the port
display = modulo.Display(port)

# Run this loop until the program is terminated
while True :
    # Call port.loop() on each iteration to process events
    port.loop()

    # Clear the display
    display.clear()

    # Draw text to the display. The color and text depend on which
    # button is pressed.
    if display.getButton(0) :
        display.setTextColor(1,0,0)
        print >>display, "Button 0"
    elif display.getButton(1) :
        display.setTextColor(0,1,0)
        print >>display, "Button 1"
    elif display.getButton(2) :
        display.setTextColor(0,0,1)
        print >>display, "Button 2"
    else :
        display.setTextColor(1,1,1)
        print >>display, "Press Button"

    # Call refresh to update the display
    display.refresh()

Events

The approach above works, but constantly checking to the buttons and redrawing the screen isn't very efficient. We can improve upon it using event callbacks.

Event callback are functions that are called automatically when certain events occur. By registering a callback function we can update the display only when a button is pressed or released.

Save this code to a file called "display-events.py", then from a terminal run "python display-events.py".

# Import the modulo python library
import modulo

# This callback function will run any time a button is pressed
def onButtonPressed(display, button) :
    # First, clear the display
    display.clear()

    # Draw text to the display. The color and text depend on which
    # button was pressed.
    if button == 0:
        display.setTextColor(1,0,0)
        print >>display, "Button 0"
    elif button == 1 :
        display.setTextColor(0,1,0)
        print >>display, "Button 1"
    elif button == 2:
        display.setTextColor(0,0,1)
        print >>display, "Button 2"

    # Call refresh to update the display
    display.refresh()

# This callback function will run any time a button is pressed
def onButtonReleased(display, button):
    # First, clear the display
    display.clear()

    # Draw the text "Press Button" in white
    display.setTextColor(1,1,1)
    print >>display, "Press Button"

    # Call refresh to update the display
    display.refresh()

# Create a new Port object using the first Modulo Controller it finds.
port = modulo.Port()

# Create a Display object attached to the port
display = modulo.Display(port)

# Register our callback functions
display.buttonPressCallback = onButtonPressed
display.buttonReleaseCallback = onButtonReleased

# Execute the onButtonReleased function to update the display
onButtonReleased(display, 0)

# Process events until the program is terminated.
port.runForever()