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Lesson 22: Touch Sensor Module

In this lesson, you will learn how to connect and program a touch sensor with the Raspberry Pi using Python. The focus will be on setting up the sensor on GPIO pin 17 and writing a simple script to detect and respond to touch and release events. This practical session is aimed at teaching the basics of sensor integration and event handling in Python, providing you with the skills needed for more advanced sensor-based projects. It’s an ideal starting point for those new to working with electronics and the Raspberry Pi.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Universal Maker Sensor Kit	94	Universal Maker Sensor Kit

You can also buy them separately from the links below.

Component Introduction	Purchase Link
Raspberry Pi 5	BUY
Touch Sensor Module	BUY
Breadboard	BUY

Wiring

Code

from gpiozero import Button
from signal import pause

# Function called when the sensor is touched
def touched():
    # Print a message indicating the sensor is touched
    print("Touched!")

# Function called when the sensor is not touched
def not_touched():
    # Print a message indicating the sensor is not touched
    print("Not touched!")

# Initialize a Button object for the touch sensor
# GPIO 17: pin connected to the sensor
# pull_up=None: disable internal pull-up/pull-down resistors
# active_state=True: high voltage is considered the active state
touch_sensor = Button(17, pull_up=None, active_state=True)

# Assign functions to sensor events
touch_sensor.when_pressed = touched
touch_sensor.when_released = not_touched

pause()  # Keep the program running to detect touch events

Code Analysis

Importing Libraries

The script starts by importing the Button class from gpiozero for interfacing with the touch sensor, and pause from the signal module to keep the program running and responsive to events.
```
from gpiozero import Button
from signal import pause
```
Defining Callback Functions

Two functions, touched and not_touched, are defined to handle touch and release events from the sensor. Each function prints a message indicating the sensor’s state.
```
def touched():
    print("Touched!")

def not_touched():
    print("Not touched!")
```
Initializing the Touch Sensor

A Button object named touch_sensor is created for the touch sensor on GPIO pin 17. The pull_up parameter is set to None to disable internal pull-up/pull-down resistors, and active_state is set to True to consider high voltage as the active state.
```
touch_sensor = Button(17, pull_up=None, active_state=True)
```
Assigning Functions to Sensor Events

The when_pressed event of the touch_sensor is linked to the touched function, and the when_released event is linked to the not_touched function. This setup allows the script to react to touch and release events from the sensor.
```
touch_sensor.when_pressed = touched
touch_sensor.when_released = not_touched
```
Keeping the Program Running

The pause() function is called to keep the program running indefinitely. This is necessary to continuously monitor and respond to touch sensor events.
```
pause()
```