2.2.4 Reed Switch Module

Introduction

In this project, we will learn about the reed switch, which is an electrical switch that operates by means of an applied magnetic field.

Components

• GPIO Extension Board

• Breadboard

• Resistor

• LED

• Reed Switch Module

Schematic Diagram

T-Board Name	physical	wiringPi	BCM
GPIO17	Pin 11	0	17
GPIO27	Pin 13	2	27
GPIO22	Pin 15	3	22

Experimental Procedures

Step 1: Build the circuit.

Step 2: Change directory.

cd /home/pi/raphael-kit/python/

Step 3: Run.

sudo python3 2.2.4_ReedSwitch.py

The green LED will light up when the code is run. If a magnet is placed close to the reed switch module, the red LED lights up; take away the magnet and the green LED lights up again.

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

ReedPin = 17
Gpin    = 27
Rpin    = 22

def setup():
    GPIO.setmode(GPIO.BCM)       #
    GPIO.setup(Gpin, GPIO.OUT)     # Set Green Led Pin mode to output
    GPIO.setup(Rpin, GPIO.OUT)     # Set Red Led Pin mode to output
    GPIO.setup(ReedPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set ReedPin's mode is input, and pull up to high level(3.3V)
    GPIO.add_event_detect(ReedPin, GPIO.BOTH, callback=detect, bouncetime=200)

def Led(x):
    if x == 0:
        GPIO.output(Rpin, 1)
        GPIO.output(Gpin, 0)
    if x == 1:
        GPIO.output(Rpin, 0)
        GPIO.output(Gpin, 1)

def detect(self):
    Led(GPIO.input(ReedPin))

def loop():
    while True:
        pass

def destroy():
    GPIO.output(Gpin, GPIO.HIGH)       # Green led on
    GPIO.output(Rpin, GPIO.LOW)       # Red led off
    GPIO.cleanup()                     # Release resource

if __name__ == '__main__':     # Program start from here
    setup()
    detect()
    try:
        loop()
    except KeyboardInterrupt:  # When 'Ctrl+C' is pressed, the child program destroy() will be  executed.
        destroy()

Code Explanation

ReedPin = 17
Gpin    = 27
Rpin    = 22

def setup():
    GPIO.setmode(GPIO.BCM)       #
    GPIO.setup(Gpin, GPIO.OUT)     # Set Green Led Pin mode to output
    GPIO.setup(Rpin, GPIO.OUT)     # Set Red Led Pin mode to output
    GPIO.setup(ReedPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set ReedPin's mode is input, and pull up to high level(3.3V)
    GPIO.add_event_detect(ReedPin, GPIO.BOTH, callback=detect, bouncetime=200)

Set the GPIO modes to BCM Numbering. ReedPin, Gpin and Rpin connects to the GPIO17, GPIO27 and GPIO22.

GPIO.add_event_detect() is used to add an event that is triggered by a change in the value (level) of ReedPin, at which point the callback function detect() is called.

def Led(x):
    if x == 0:
        GPIO.output(Rpin, 1)
        GPIO.output(Gpin, 0)
    if x == 1:
        GPIO.output(Rpin, 0)
        GPIO.output(Gpin, 1)

Define a function Led() to turn the two LEDs on or off. If x=0, the red LED lights up; otherwise, the green LED will be lit.

def detect(self):
Led(GPIO.input(ReedPin))

In this callback function, the value of the reed switch is used to control the 2 LEDs.

Phenomenon Picture