Lesson 4 Shock Switch

Introduction

A vibration switch, also called spring switch or shock sensor, is an electronic switch which induces shock force and transfers the result to a circuit device thus triggering it to work. It contains the following parts: conductive vibration spring, switch body, trigger pin, and packaging agent.

Components

– 1 * Raspberry Pi

– 1 * Breadboard

– 1 * Network cable (or USB wireless network adapter)

– 1 * Shock switch module

– 1 * Dual-color Common-Cathode LED module

– Jumper wires

Experimental Principle

The shock switch works like this: the conductive vibration spring and trigger pin are precisely placed in the switch and fixed by adhesive. Normally, the spring and the trigger pin are separated. Once the sensor detects shock, the spring will vibrate and contact with the trigger pin, thus conducting and generating trigger signals.

In this experiment, a dual-color LED module is used to indicate shock signals. When the shock switch inducts shock signals, the LED will light up.

Experimental Procedures

Step 1: Build the circuit

Shock switch connection: connect pin S of the Shock switch module to GPIO0 of the Raspberry Pi; GND to GND; pin + to 3.3V

Dual-color LED module connection: connect pin R of the dual-color LED module to GPIO1 of the Raspberry Pi; GND to GND

Step 2: Edit and save the code (see path/Rpi_SensorKit_code/06_shockSwitch/shockSwitch.c)

Step 3: Compile

              gcc  shockSwitch.c  -lwiringPi

Step 4: Run

              ./a.out

Shake the switch and you will see the string “Detected shaking ! count = ?” printed on screen, and the LED will light up.

shockSwitch.c 

#include <wiringPi.h>
#include <stdio.h>

#define ShockPin      0
#define LedPin        1

int main(void)
{
	int count;

	if(wiringPiSetup() == -1){ //when initialize wiring failed,print messageto screen
		printf("setup wiringPi failed !");
		return 1; 
	}
	
	pinMode(ShockPin,  INPUT);
	pinMode(LedPin,   OUTPUT);

	while(1){
		if(digitalRead(ShockPin) == LOW){
			delay(10);
			if(digitalRead(ShockPin) == LOW){
				count++;
				printf("Detected shaking ! count = %d\n", count);
				digitalWrite(LedPin, !digitalRead(LedPin));			
			}
		}	
	}

	return 0;
}

Python Code

#!/usr/bin/env python
import RPi.GPIO as GPIO

ShockPin = 11
LedPin   = 12

Led_status = 1

def setup():
	GPIO.setmode(GPIO.BOARD)       # Numbers GPIOs by physical location
	GPIO.setup(LedPin, GPIO.OUT)   # Set LedPin's mode is output
	GPIO.setup(ShockPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)
	GPIO.output(LedPin, GPIO.HIGH) # Set LedPin high(+3.3V) to off led

def swLed(ev=None):
	global Led_status
	Led_status = not Led_status
	GPIO.output(LedPin, Led_status)  # switch led status(on-->off; off-->on)
        print "led: " + ("on" if Led_status else "off")

def loop():
	GPIO.add_event_detect(ShockPin, GPIO.FALLING, callback=swLed, bouncetime=200) # wait for falling
	while True:
		pass   # Don't do anything

def destroy():
	GPIO.output(LedPin, GPIO.LOW)      # led off
	GPIO.cleanup()                     # Release resource

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