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Button Switch and Simple Loop Lighting of LEDs

Tutorial: Button Switch and Simple Loop Lighting of LEDs

In this tutorial, you learn how to:

  • Wire a Button Switch and Two LEDs to your Raspberry Pi
  • Code your Button Switch in a simple loop

A button switch is a type of electrical switch that is activated by pressing a button. They are commonly used in electronic devices to turn them on or off, or to perform other functions such as adjusting the volume or changing the channel. The benefits of button switches include their ease of use and the ability to control electronic devices with a simple press of a button. Additionally, button switches are relatively inexpensive and widely available, making them a popular choice for use in a wide range of electronic devices.

Following the diagram below, you'll wire a button switch to two LEDs, one red, another green, to show the states of the circuit. Note the various states of the LED's when pressing the button switch:

  1. When first starting, the red and green LEDs are both off.

  2. When the button switch is pressed, the green LED turns on, while the red remains off.

  3. When the button switch is released, the green LED turns off, and the red turns on (until the button switch is pressed again).

    :::image type="content" source="media/tutorial-rasp-switchledsimple/switch2LEDs.gif" alt-text="Button switch with 2 LEDs":::

Prerequisites

Completed the...

Supplies:

Quantity Item
1 Breadboard
4 Male to male jumper wires
1 Button switch
1 Green LED
1 Red LED
2 220Ω Resistors
1 (optional) GPIO Extension Board
1 (optional) 40 pin GPIO cable

Wire a Button Switch and Two LEDs to your Raspberry Pi

Below is the circuit we'll construct.

lnk_ledswitchsimpleschematic

Following the diagram below:

  1. Connect the button switch to the breadboard

  2. Connect the red and green LEDs having the cathode (long lead) on a connection terminal and the anode (shorter lead) connected to the breadboard rail.

  3. Connect one lead of your 220 resistor to the rail (anode leads from the LEDs), and the other lead to ground.

    :::image type="content" source="media/tutorial-rasp-switchledsimple/simpleswitchled.png" alt-text="Button switch with simple loop":::

Code your Button Switch

In this section you'll code using the GPIO.input for your button switch with
GPIO.setup(button, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

While in a loop you'll check the GPIO.input(button) for a HIGH or LOW incoming signal to indicate which LED will be turned on or off. The time.sleep(0.01) is needed to allow the processor time to do other things. Having your Raspberry Pi running in a continuous loop occupies its processor, but makes for a very responsive button.

  1. Connect to your Raspberry Pi using Visual Studio Code.

  2. Create a file switchledsimple.py in your cloned GitHub under the python/raspberrypi directory, for example ~/repos/IoT/python/raspberrypi/switchledsimple.py

  3. Import statements and variables.

    import RPi.GPIO as GPIO
import time

# Pin assignments (GPIO.BOARD)
button = 11 # GPIO17
led_green = 13 # GPIO27
led_red = 15 # GPIO22

  4. Copy and Paste the main method.

    def main():
    GPIO.setmode(GPIO.BOARD)
    GPIO.setup(led_green, GPIO.OUT)
    GPIO.setup(led_red, GPIO.OUT)
    GPIO.output(led_green, GPIO.LOW)
    GPIO.output(led_red, GPIO.LOW)

    GPIO.setup(button, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

    print("Press Ctrl-C to quit'")
    last = 0
    cur = 0
    cnt = 0

    try:
        while True:
            cur = GPIO.input(button)
            if cur != last:
                if GPIO.input(button) == GPIO.LOW:
                    GPIO.output(led_green, GPIO.LOW)
                    GPIO.output(led_red, GPIO.HIGH)
                    cnt += 1
                    print("Button Released. Count = {0}".format(cnt))
                else:
                    GPIO.output(led_green, GPIO.HIGH)
                    GPIO.output(led_red, GPIO.LOW)
                    print("Button Pushed")
                last = cur
            time.sleep(0.01)
    except KeyboardInterrupt:
        print("Program shut down by user")
    finally:
        GPIO.cleanup()
        print("Cleaning up and shutting down")

if __name__ == "__main__":
    main()

Run It

  1. Start the debugger in Visual Studio Code
  2. Verify the behavior of the LED lighting.
  3. Be sure to gracefully shut down the program by typing ctrl-c. That way your GPIO ports have been cleaned up and ready for your next project.

Next steps

Tutorial: Button Switch and Waiting for Edge Lighting of LEDs