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

Step 3: Run.

sudo python3 1.3.3_Relay.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. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3

import RPi.GPIO as GPIO
import time

# Set GPIO17 as control pin
relayPin = 17

# Define a setup function for some setup
def setup():
    # Set the GPIO modes to BCM Numbering
    GPIO.setmode(GPIO.BCM)
    # Set relayPin's mode to output,
    # and initial level to High(3.3v)
    GPIO.setup(relayPin, GPIO.OUT, initial=GPIO.HIGH)

# Define a main function for main process
def main():
    while True:
        print ('Relay open...')
        # Tick
        GPIO.output(relayPin, GPIO.LOW)
        time.sleep(1)
        print ('...Relay close')
        # Tock
        GPIO.output(relayPin, GPIO.HIGH)
        time.sleep(1)

# Define a destroy function for clean up everything after
# the script finished
def destroy():
    # Turn off LED
    GPIO.output(relayPin, GPIO.HIGH)
    # Release resource
    GPIO.cleanup()

# If run this script directly, do:
if __name__ == '__main__':
    setup()
    try:
        main()
    # When 'Ctrl+C' is pressed, the child program
    # destroy() will be  executed.
    except KeyboardInterrupt:
        destroy()

Code Explanation

GPIO.output(relayPin, GPIO.LOW)

Set the pins of transistor as low level to let the relay open, LED does not turn on.

time.sleep(1)

wait for 1 second.

GPIO.output(relayPin, GPIO.HIGH)

Set the pins of the transistor as low level to actuate the relay, LED lights up.