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.

Required Components

• 1 * Raspberry Pi

• 1 * Breadboard

• 1 * Touch sensor 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	GPIO Extension Board	Touch Sensor Module
GPIO0	GPIO17	SIG
3.3V	3V3	VCC
GND	GND	GND

Raspberry Pi	GPIO Extension Board	Dual-Color LED Module
GPIO1	GPIO18	R
GND	GND	GND
GPIO2	GPIO27	G

For C Users:

Step 2: Change directory.

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

Step 3: Compile.

gcc touch_switch.c -lwiringPi

Note

If it does not work after running, or there is an error prompt wiringPi.h: No such file or directory, please refer to WiringPi to install it.

Step 4: Run.

sudo ./a.out

Code

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

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

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;
}

For Python Users:

Step 2: Change directory.

cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run.

sudo python3 24_touch_switch.py

Code

#!/usr/bin/env python3
import RPi.GPIO as GPIO

TouchPin = 11
Gpin   = 13
Rpin   = 12

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()

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