Lesson 24 Touch Switch

Introduction

A touch sensor operate with the conductivity of human body. When you touch the metal on the base electrode of the transistor, the level of pin SIG will turn over.

Components

– 1 * Raspberry Pi

– 1 * Breadboard

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

– 1 * Touch Switch module

– 1 * Dual-Color LED module

– 2 * 3-Pin anti-reverse cable

Experimental Principle

In this experiment, touch the base electrode of the transistor by fingers to make it conduct as human body itself is a kind of conductor and an antenna that can receive electromagnetic waves in the air. These electromagnetic wave signals collected from the human body are amplified by the transistor and processed by the comparator on the module to output steady signals. The schematic diagram:

Experimental Procedures

Step 1: Build the circuit

Raspberry Pi	Touch Switch Module
GPIO0	SIG
5V	VCC
GND	GND

Raspberry Pi	Dual-Color LED Module
GPIO1	R
GND	GND
GPIO2	G

For C language users:

Step 2: Change directory

 cd /home/pi/SunFounder_SensorKit_for_RPi2/C/24_touch_switch/

Step 3: Compile

gcc touch_switch.c -lwiringPi

Step 4: Run

sudo ./a.out

For Python users:

Step 2: Change directory

 cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run

sudo python 24_touch_switch.py

Now, touch the metal disk, you can see the LED change its colors and “ON” and “OFF” printed on the screen.

 C Code

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

#define TouchPin	0
#define Gpin		1
#define Rpin		2

int tmp = 0;

void LED(int color)
{
	pinMode(Gpin, OUTPUT);
	pinMode(Rpin, OUTPUT);
	if (color == 0)
	{
		digitalWrite(Rpin, HIGH);
		digitalWrite(Gpin, LOW);
	}
	else if (color == 1)
	{
		digitalWrite(Rpin, LOW);
		digitalWrite(Gpin, HIGH);
	}
	else
		printf("LED Error");
}

void Print(int x){
	if (x != tmp){
		if (x == 0)
			printf("...ON\n");
		if (x == 1)
			printf("OFF..\n");
		tmp = x;
	}
}

int main(void)
{
	if(wiringPiSetup() == -1){ //when initialize wiring failed,print messageto screen
		printf("setup wiringPi failed !");
		return 1; 
	}

	pinMode(TouchPin, INPUT);
	
	while(1){
		LED(digitalRead(TouchPin));	
		Print(digitalRead(TouchPin));	
	}
	return 0;
}

Python Code 

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

TouchPin = 11
Gpin   = 12
Rpin   = 13

tmp = 0

def setup():
	GPIO.setmode(GPIO.BOARD)       # Numbers GPIOs by physical location
	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(TouchPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set BtnPin's mode is input, and pull up to high level(3.3V)

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 Print(x):
	global tmp
	if x != tmp:
		if x == 0:
			print '    **********'
			print '    *     ON *'
			print '    **********'
	
		if x == 1:
			print '    **********'
			print '    * OFF    *'
			print '    **********'
		tmp = x

def loop():
	while True:
		Led(GPIO.input(TouchPin))
		Print(GPIO.input(TouchPin))

def destroy():
	GPIO.output(Gpin, GPIO.HIGH)       # Green led off
	GPIO.output(Rpin, GPIO.HIGH)       # Red 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()