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1.3.3 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.

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

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Transistor	BUY
Relay	BUY
Diode	BUY

Schematic Diagram¶

Experimental Procedures¶

Step 1: Build the circuit.

Step 2: Open the code file.

cd ~/raphael-kit/python-pi5

Step 3: Run.

sudo python3 1.3.3_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 raphael-kit/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, starting in the 'off' state
relay = OutputDevice(17, initial_value=False)

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

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

Initializes an OutputDevice object for the relay connected to GPIO pin 17. The initial_value=False sets the relay to the off state initially (assuming active low configuration).
```
# Initialize the relay connected to GPIO pin 17, starting in the 'off' state
relay = OutputDevice(17, initial_value=False)
```

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

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