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2.3 Slide Switch

Introduction

In this project, we will learn how to use a slide switch to control two LEDs. Slide switches are commonly used as power switches in electronic circuits. Here, we demonstrate its functionality using a breadboard setup. While slide switches are often soldered onto PCBs for stability, we will use it in a flexible breadboard configuration to better understand its operation.

What You’ll Need

To complete this project, gather the following components:

COMPONENT	PURCHASE LINK
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Slide Switch	BUY
Capacitor	BUY
Fusion HAT+	-
Raspberry Pi	-

Circuit Diagram

The Slide Switch middle pin is connected to GPIO17, while two LEDs are connected to GPIO22 and GPIO27. The switch toggles between the two LEDs, alternately lighting them up.

Wiring Diagram

Follow these steps to build the circuit:

Connect the middle pin of the Slide Switch to GPIO17.
Connect one side pin of the Slide Switch to GND and the other to VCC.
Connect LED1’s anode to GPIO22 via a current-limiting resistor.
Connect LED2’s anode to GPIO27 via a current-limiting resistor.
Connect the cathodes of both LEDs to GND.

Running the Example

All example code used in this tutorial is available in the ai-lab-kit directory. Follow these steps to run the example:

cd ~/ai-lab-kit/python/
sudo python3 2.3_SlideSwitch.py

This Python script demonstrates the use of a slide switch to control two LEDs on the Fusion HAT+. When executed:

Slide Switch Activated:
- Turns off LED1 (connected to GPIO pin 22).
- Turns on LED2 (connected to GPIO pin 27).
Slide Switch Not Activated:
- Turns on LED1.
- Turns off LED2.
The program continuously checks the state of the slide switch every 0.5 seconds and adjusts the LEDs accordingly.
The script runs indefinitely until interrupted by pressing Ctrl+C.

Code

Here’s the Python code to control the LEDs based on the state of the Slide Switch:

#!/usr/bin/env python3
from fusion_hat.pin import Pin, Mode, Pull
from time import sleep  # Import sleep for delay

# Initialize slider (Button) on GPIO pin 17
slider = Pin(17, mode=Mode.IN, pull=Pull.DOWN)

# Initialize LED1 connected to GPIO pin 22
led1 = Pin(22,mode=Mode.OUT)
# Initialize LED2 connected to GPIO pin 27
led2 = Pin(27,mode=Mode.OUT)

try:
   # Continuously monitor the state of the slider and control LEDs accordingly
   while True:
      if slider.value() == 1:  # Check if the slider is pressed
            led1.off()  # Turn off LED1
            led2.on()   # Turn on LED2
      else:  # If the sensor is not pressed
            led1.on()   # Turn on LED1
            led2.off()  # Turn off LED2

      sleep(0.5)  # Pause for 0.5 seconds before rechecking the sensor state

except KeyboardInterrupt:
   # Handle a keyboard interrupt (Ctrl+C) for a clean exit from the loop
   pass

Understanding the Code

Library Imports

Import necessary libraries for GPIO control and adding delays.

from fusion_hat.pin import Pin, Mode, Pull
from time import sleep  # Import sleep for delay

Component Initialization

Configure the Slide Switch as a Button and initialize two LEDs connected to GPIO pins 22 and 27.

# Initialize slider (Button) on GPIO pin 17
slider = Pin(17, mode=Mode.IN, pull=Pull.DOWN)

# Initialize LED1 connected to GPIO pin 22
led1 = Pin(22,mode=Mode.OUT)
# Initialize LED2 connected to GPIO pin 27
led2 = Pin(27,mode=Mode.OUT)

State Monitoring and LED Control

In the main loop, the program monitors the state of the Slide Switch. When the switch is toggled, it alternates between turning on LED1 and LED2.

# Continuously monitor the state of the slider and control LEDs accordingly
while True:
   if slider.value() == 1:  # Check if the slider is pressed
         led1.off()  # Turn off LED1
         led2.on()   # Turn on LED2
   else:  # If the sensor is not pressed
         led1.on()   # Turn on LED1
         led2.off()  # Turn off LED2

   sleep(0.5)  # Pause for 0.5 seconds before rechecking the sensor state

Graceful Exit

The script terminates gracefully when interrupted using Ctrl+C.
```
except KeyboardInterrupt:
    pass
```

Troubleshooting

Slide Switch Does Not Respond
- Cause: The slide switch is not connected properly, or the pull-up resistor configuration is incorrect.
- Solution: Confirm that the slide switch is connected to GPIO pin 17 and ground. Ensure PULL_DOWN matches the switch configuration.
LEDs Flicker or Behave Erratically
- Cause: Debounce issues with the slide switch.
- Solution: Add software debounce to stabilize the input signal:
```
if slider.value() == 1:
   sleep(0.05)  # Debounce delay
```

Extendable Ideas

Two-Way Switch Control

Combine two slide switches to control LEDs in a more complex setup, such as a simple light control panel.

Audio Feedback

Add a buzzer that sounds when the slide switch is activated:

from fusion_hat import Buzzer
buzzer = Buzzer(Pin(22))
if slider.value() == 1:
   buzzer.on()
else:
   buzzer.off()

Conclusion

This project demonstrates how to use a Slide Switch with the Fusion HAT+ to control LEDs. Slide Switches are versatile and durable components, often employed in user interfaces and control systems. Experimenting with them opens up possibilities for creating advanced and interactive projects.