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2.5 Touch Switch Module

Introduction

In this project, we explore the use of a Touch Switch Module. This component replaces traditional mechanical switches and offers benefits such as precise control, fine touch sensitivity, and minimal mechanical wear. Touch switches are commonly used in modern appliances and devices where reliability and ease of operation are essential.

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
Touch Switch Module	BUY
Fusion HAT+	-
Raspberry Pi	-

Circuit Diagram

Below is the schematic diagram showing how to connect the Touch Switch Module to the Raspberry Pi and LEDs:

Wiring Diagram

Follow these steps to build the circuit:

Connect the Touch Switch Module output pin to GPIO17.
Connect LED1 anode to GPIO22 and LED2 anode to GPIO27 via appropriate resistors.
Connect the cathodes of both LEDs and the Touch Switch ground pin 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 2.5_TouchSwitch.py

This Python script uses a touch sensor to control two LEDs connected to a Raspberry Pi. When executed:

Touch Sensor Pressed:
- Prints “You touch it!” to the console.
- Turns off LED1 (connected to GPIO pin 22).
- Turns on LED2 (connected to GPIO pin 27).
Touch Sensor Not Pressed:
- LED1 turns on.
- LED2 turns off.
The program continuously monitors the touch sensor’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 controls two LEDs based on the state of the Touch Switch Module:

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

# Initialize touch sensor (Button) on GPIO pin 17
touch_sensor = 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 touch sensor and control LEDs accordingly
   while True:
      if touch_sensor.value() == 1:  # Check if the touch sensor is pressed
            print('You touch it!')  # Output message indicating sensor activation
            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 Import

The fusion_hat library is used to simplify GPIO control, and the sleep function provides delay functionality.
```
from fusion_hat.pin import Pin, Mode, Pull
from time import sleep  # Import sleep for delay
```

Component Initialization

The touch sensor is configured as a button on GPIO17, and two LEDs are initialized on GPIO22 and GPIO27.

# Initialize touch sensor (Button) on GPIO pin 17
touch_sensor = 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)

Main Loop

The program continuously checks the state of the Touch Switch Module. When touched, LED2 turns on and LED1 off; otherwise, LED1 is on, and LED2 is off.

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

Interrupt Handling

A try-except block ensures that the program exits cleanly upon receiving a keyboard interrupt (Ctrl+C).
```
except KeyboardInterrupt:
    pass
```

Troubleshooting

No Response from Touch Sensor
- Cause: Incorrect wiring or GPIO pin configuration.
- Solution: Ensure the touch sensor is connected to GPIO pin 17 and ground, and verify that PULL_DOWN matches the sensor’s active-low configuration.
Sensor Always Reads Pressed or Not Pressed
- Cause: Faulty sensor or wiring.
- Solution: Test the sensor with a multimeter or replace it. Check for loose or incorrect connections.
LEDs Flicker or Behave Erratically
- Cause: Button debounce issues.
- Solution: Add software debounce to stabilize the input signal:
```
if touch_sensor.value() == 1:
   sleep(0.05)  # Debounce delay
```

Extendable Ideas

Touch Duration Detection

Add functionality to detect how long the touch sensor is pressed and adjust LED behavior:

from time import time
start_time = None

def handle_touch():
   global start_time
   if touch_sensor.value() == 1:
      start_time = time()
   else:
      duration = time() - start_time
      print(f"Sensor was touched for {duration:.2f} seconds")

Adjustable Delay

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

Conclusion

This project demonstrates how to use a Touch Switch Module with the Fusion HAT+ to control LEDs. Touch switches are versatile and reliable components, often used in modern devices for seamless and intuitive interaction.