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2.2 Micro Switch

Introduction

In this project, we will explore how to use a Micro Switch to control two LEDs. A Micro Switch is a highly sensitive component that requires minimal compression to activate. It is often used in safety systems to prevent machinery or doors from operating under unsafe conditions.

What You’ll Need

To complete this project, you will need the following components:

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

Circuit Diagram

The Micro Switch is connected to GPIO17, and two LEDs are connected to GPIO22 and GPIO27. When the Micro Switch is pressed, the red LED lights up; when released, the yellow LED turns on.

Wiring Diagram

Follow these steps to build the circuit:

Connect one terminal of the Micro Switch to GPIO17 and the other to the ground (GND).
Connect the anodes of the two LEDs to GPIO22 (yellow) and GPIO27 (red) through current-limiting resistors.
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 2.2_MicroSwitch.py

This Python script controls two LEDs based on the state of a micro switch connected to a Raspberry Pi. When executed:

Micro Switch Pressed:
- LED1 (connected to GPIO pin 22) turns on.
- LED2 (connected to GPIO pin 27) turns off.
Micro Switch Released:
- LED1 turns off.
- LED2 turns on.
The program continuously checks the micro switch’s state every 0.5 seconds and adjusts the LEDs accordingly.
The script runs indefinitely until interrupted by pressing Ctrl+C.

Code

The following Python code toggles between two LEDs based on the state of the Micro Switch:

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

# Initialize micro switch on GPIO pin 17
micro_switch = 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 check the state of the micro switch and control LEDs accordingly
   while True:
      if micro_switch.value() == 1:  # If the micro switch is pressed
            led1.high()       # Turn on LED1
            led2.low()      # Turn off LED2
      else:  # If the micro switch is not pressed
            led1.low()      # Turn off LED1
            led2.high()       # Turn on LED2

      sleep(0.5)  # Pause for 0.5 seconds before checking the switch again

except KeyboardInterrupt:
   # Handle KeyboardInterrupt (Ctrl+C) to exit the loop gracefully
   pass

Understanding the Code

Library Import

The fusion_hat library provides simple GPIO control, and the time library enables delays.

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

Component Initialization

The Micro Switch is connected to GPIO17 with pull-up disabled, while the LEDs are connected to GPIO22 and GPIO27.

# Initialize micro switch on GPIO pin 17
micro_switch = 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)

Switch State Handling

The program checks the state of the Micro Switch in a loop. When pressed, LED1 turns on and LED2 off. When released, LED1 turns off and LED2 on.

while True:
   if micro_switch.value() == 1:
      led1.on()
      led2.off()
   else:
      led1.off()
      led2.on()
   sleep(0.5)

Interrupt Handling

The try-except block ensures the script exits cleanly when interrupted using Ctrl+C.
```
except KeyboardInterrupt:
   pass
```

Troubleshooting

LEDs Do Not Respond
- Cause: Incorrect GPIO wiring or pin configuration.
- Solution: Ensure LED1 is connected to GPIO pin 22, LED2 to GPIO pin 27, and both LEDs have appropriate resistors. Verify the micro switch connection to GPIO pin 17.
Micro Switch Not Detected
- Cause: The micro switch might not be configured properly or needs a pull-up/pull-down resistor.
- Solution: Confirm that pull = Pin.PULL_UP matches your switch configuration. If the switch requires a pull-up, enable it in the initialization.
LEDs Flicker or Behave Erratically
- Cause: Button debounce issues.
- Solution: Add software debounce by introducing a short delay after detecting a press:
```
if micro_switch.value() == 1:
   sleep(0.05)  # Debounce delay
```

Extendable Ideas

Adjustable Delay

Allow the user to change the delay dynamically to fine-tune LED responsiveness:
```
delay = float(input("Enter delay in seconds: "))
while True:
   sleep(delay)
```

Audio Feedback

Add a buzzer to provide an audible signal when the switch is pressed or released:

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

Conclusion

This project demonstrates how to use a Micro Switch to control LEDs with the Fusion HAT+. Micro Switches are versatile components widely used in safety systems, user interfaces, and industrial controls. Experimenting with them can open up opportunities for creating more advanced projects.