Raspberry Pi - Touch Sensor - Relay
This tutorial instructs you how to use the Raspberry Pi and touch sensor to control the relay. By connecting the relay to a soleniod lock, light bulb, LED strip, motor, or actuator..., we can use a touch sensor to control the them. We will learn two different applications:
Application 1 - The relay state is synchronized with the touch sensor state. In detail:
- Raspberry Pi turns on the relay when the touch sensor is being touched.
- Raspberry Pi turns off the relay when the touch sensor is NOT being touched.
Application 2 - The relay state is toggled each time the touch sensor is touched. More specifically:
- If Raspberry Pi detects that the touch sensor has been touched (changing from a LOW state to a HIGH state), it will turn ON the relay if it's currently OFF, or turn OFF the relay if it's currently ON.
- Releasing the touch sensor does not affect to the relay state.
Hardware Preparation
Or you can buy the following sensor kits:
| 1 | × | DIYables Sensor Kit (30 sensors/displays) | |
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you. We appreciate your support.
Overview of Relay and Touch Sensor
If you are unfamiliar with relay and touch sensor (including pinout, operation, and programming), the following tutorials can help:
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
Application 1 - The relay state is in sync with the touch sensor state
Detailed Instructions
- Make sure you have Raspbian or any other Raspberry Pi compatible operating system installed on your Pi.
- Make sure your Raspberry Pi is connected to the same local network as your PC.
- Make sure your Raspberry Pi is connected to the internet if you need to install some libraries.
- If this is the first time you use Raspberry Pi, See how to set up the Raspberry Pi
- Connect your PC to the Raspberry Pi via SSH using the built-in SSH client on Linux and macOS or PuTTY on Windows. See to how connect your PC to Raspberry Pi via SSH.
- Make sure you have the RPi.GPIO library installed. If not, install it using the following command:
sudo apt-get update
sudo apt-get install python3-rpi.gpio
- Create a Python script file touch_sensor_relay.py and add the following code:
# This Raspberry Pi code was developed by newbiely.com
# This Raspberry Pi code is made available for public use without any restriction
# For comprehensive instructions and wiring diagrams, please visit:
# https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-touch-sensor-relay
import RPi.GPIO as GPIO
# Set the GPIO mode (BCM or BOARD)
GPIO.setmode(GPIO.BCM)
# Define the GPIO pin number to which the relay is connected
RELAY_PIN = 20
# Define the GPIO pin number to which the touch sensor is connected
TOUCH_SENSOR_PIN = 18
# Set up the GPIO pins
GPIO.setup(TOUCH_SENSOR_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP) # Input with pull-up resistor
GPIO.setup(RELAY_PIN, GPIO.OUT) # Output
try:
while True:
touch_state = GPIO.input(TOUCH_SENSOR_PIN)
if touch_state == GPIO.HIGH:
print("The sensor is touched")
GPIO.output(RELAY_PIN, GPIO.HIGH) # Turn the relay on
else:
print("The sensor is not touched")
GPIO.output(RELAY_PIN, GPIO.LOW) # Turn the relay off
except KeyboardInterrupt:
GPIO.output(RELAY_PIN, GPIO.LOW) # Turn off the relay
GPIO.cleanup()
- Save the file and run the Python script by executing the following command in the terminal:
python3 touch_sensor_relay.py
- Touch your finger on the touch sensor and hold it for a few seconds, then release it.
- Check out the change in the relay's condition. You will see that the relay state is in sync with the touch sensor state.
The script runs in an infinite loop continuously until you press Ctrl + C in the terminal.
Code Explanation
Check out the line-by-line explanation contained in the comments of the source code!
Application 2 - Touch Sensor toggles Relay
Detailed Instructions
- Create a Python script file touch_sensor_toggle_relay.py and add the following code:
# This Raspberry Pi code was developed by newbiely.com
# This Raspberry Pi code is made available for public use without any restriction
# For comprehensive instructions and wiring diagrams, please visit:
# https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-touch-sensor-relay
import RPi.GPIO as GPIO
import time
# Constants won't change
TOUCH_SENSOR_PIN = 16 # The number of the touch sensor pin
RELAY_PIN = 18 # The number of the relay pin
# Variables will change
relay_state = GPIO.LOW # The current state of the relay
prev_touch_state = GPIO.LOW # The previous state of the touch sensor
touch_state = GPIO.LOW # The current state of the touch sensor
# Set up GPIO
GPIO.setmode(GPIO.BCM) # Use BCM GPIO numbering
GPIO.setup(RELAY_PIN, GPIO.OUT) # Initialize the relay pin as an output
GPIO.setup(TOUCH_SENSOR_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP) # Initialize the touch sensor pin as a pull-up input
try:
while True:
# Read the state of the touch sensor value
prev_touch_state = touch_state # Save the last state
touch_state = GPIO.input(TOUCH_SENSOR_PIN) # Read new state
if prev_touch_state == GPIO.LOW and touch_state == GPIO.HIGH:
time.sleep(0.1) # 100 milliseconds debounce time
print("The sensor is touched")
# Toggle the state of the relay
if relay_state == GPIO.LOW:
relay_state = GPIO.HIGH
else:
relay_state = GPIO.LOW
# Control relay according to the toggled state
GPIO.output(RELAY_PIN, relay_state)
except KeyboardInterrupt:
# Clean up GPIO on program exit
GPIO.cleanup()
- Save the file and run the Python script by executing the following command in the terminal:
python3 touch_sensor_toggle_relay.py
- Touch and release the touch sensor several times.
- Check out the change in the relay's state. You'll notice that the relay will switch on or off one time whenever you place your finger on the touch sensor.