Lesson 6 Button Module

Introduction

In this lesson, we will use a button module to control a dual-color LED module.

Components

– 1 * Raspberry Pi

– 1 * Breadboard

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

– 1 * Button module

– 1 * Dual-color LED module

– 2 * 3-Pin anti-reverse cable

Experimental Principle

Use a normally open button as an input device of Raspberry Pi. When the button is pressed, the General Purpose Input/Output (GPIO) connected to the button will change to low level (0V). You can detect the state of the GPIO through programming. That is, if the GPIO turns into low level, it means the button is pressed, so you can run the corresponding code. In this experiment, we will print a string on the screen and control an LED.

The schematic diagram:

Experimental Procedures

Step 1: Build the circuit

Raspberry Pi	Button 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/06_button/

Step 3: Compile

gcc button.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 06_button.py

The LED on the module will flash green. If you press the button, “Button pressed” will be printed on the screen and the LED will flash red. If you release the button, “Button released” will be printed on the screen and the LED will flash green again.

C Code

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

#define BtnPin		0
#define Gpin		1
#define Rpin		2

void LED(char* color)
{
	pinMode(Gpin, OUTPUT);
	pinMode(Rpin, OUTPUT);
	if (color == "RED")
	{
		digitalWrite(Rpin, HIGH);
		digitalWrite(Gpin, LOW);
	}
	else if (color == "GREEN")
	{
		digitalWrite(Rpin, LOW);
		digitalWrite(Gpin, HIGH);
	}
	else
		printf("LED Error");
}

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

	pinMode(BtnPin, INPUT);
	LED("GREEN");
	
	while(1){
		if(0 == digitalRead(BtnPin)){
			delay(10);
			if(0 == digitalRead(BtnPin)){
				LED("RED");	
				printf("Button is pressed\n");	
			}
		}
		else if(1 == digitalRead(BtnPin)){
			delay(10);
			if(1 == digitalRead(BtnPin)){
				while(!digitalRead(BtnPin));
				LED("GREEN");
			}
		}
	}
	return 0;
}

Python Code

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

BtnPin = 11
Gpin   = 12
Rpin   = 13

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(BtnPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set BtnPin's mode is input, and pull up to high level(3.3V)
	GPIO.add_event_detect(BtnPin, 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 Print(x):
	if x == 0:
		print '    ***********************'
		print '    *   Button Pressed!   *'
		print '    ***********************'

def detect(chn):
	Led(GPIO.input(BtnPin))
	Print(GPIO.input(BtnPin))

def loop():
	while True:
		pass

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()