1.3.4 Relay

Introduction

In this project, we will learn to use a relay. It is one of the commonly used components in automatic control system. When the voltage, current, temperature, pressure, etc., reaches, exceeds or is lower than the predetermined value, the relay will connect or interrupt the circuit, to control and protect the equipment.

Required Components

In this project, we need the following components.

Schematic Diagram

Experimental Procedures

Step 1: Build the circuit.

Step 2: Open the code file.

cd ~/davinci-kit-for-raspberry-pi/python-pi5

Step 3: Run.

sudo python3 1.3.4_Relay_zero.py

While the code is running, the LED lights up. In addition, you can hear a ticktock caused by breaking normally close contact and closing normally open contact.

Code

Note

You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like davinci-kit-for-raspberry-pi/python-pi5. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3
from gpiozero import OutputDevice  # Import the class for controlling GPIO pins
from time import sleep  # Import the sleep function for delay

# Initialize the relay connected to GPIO pin 17
relay = OutputDevice(17)

try:
    # Loop to continuously toggle the relay's state every second
    while True:
        print('Relay open...')  # Inform that the relay is being activated
        relay.on()  # Turn on the relay (assuming active low configuration)
        sleep(1)   # Maintain the relay in the on state for 1 second

        print('...Relay close')  # Inform that the relay is being deactivated
        relay.off()  # Turn off the relay
        sleep(1)   # Maintain the relay in the off state for 1 second

except KeyboardInterrupt:
    # Handle a keyboard interrupt (Ctrl+C) to exit the loop
    relay.off()  # Ensure the relay is turned off before exiting
    pass

Code Explanation

1. It imports OutputDevice from gpiozero for controlling GPIO pins and sleep from time for adding delays.

   #!/usr/bin/env python3
   from gpiozero import OutputDevice  # Import the class for controlling GPIO pins
   from time import sleep  # Import the sleep function for delay
   

2. Initializes an OutputDevice object for the relay connected to GPIO pin 17.

   # Initialize the relay connected to GPIO pin 17
   relay = OutputDevice(17)
   

3. Inside the try block, a while True loop continuously toggles the relay’s state. The relay is turned on and off with a 1-second delay between each state, accompanied by console print statements.

   try:
       # Loop to continuously toggle the relay's state every second
       while True:
           print('Relay open...')  # Inform that the relay is being activated
           relay.on()  # Turn on the relay (assuming active low configuration)
           sleep(1)   # Maintain the relay in the on state for 1 second
   
           print('...Relay close')  # Inform that the relay is being deactivated
           relay.off()  # Turn off the relay
           sleep(1)   # Maintain the relay in the off state for 1 second
   

4. Catches a KeyboardInterrupt (like Ctrl+C) to allow for graceful script termination. The relay is turned off before exiting the script.

   except KeyboardInterrupt:
   # Handle a keyboard interrupt (Ctrl+C) to exit the loop
   relay.off()  # Ensure the relay is turned off before exiting
   pass