Push Buttons | Technology Tutorials

In this lesson we will show how you can control LED’s from push buttons. In order to get started, you will want to expand the circuit we built in LESSON 29 to include two LEDs. The schematic below shows how you will want to hook things up (Also, remember you can see the Raspberry Pi pinout in LESSON 25). Also, as we have mentioned before, if you want to follow along with us in these lessons you can get a kit that has all the gear you need HERE.

Raspberry Pi LED Circuit — This Circuit Controls two LED from Push Buttons Using the Raspberry Pi

In the video lesson, we take you through the code step-by-step. We use the techniques learned in LESSON 29 to detect if a button has been pushed. We introduce two new variables, BS1 and BS2, so indicate the state of the LED’s. A BS1=False means the LED1 is off. A BS1=True means the LED is on. This concept allows us to determine whether we should turn the LED on or off when the button is pushed. Basically, we want to put it in the opposite state when a button is pushed. The code is below. The video shows how it works.

from time import sleep     # Import sleep Library
import RPi.GPIO as GPIO    # Import GPIO Library 
GPIO.setmode(GPIO.BOARD)   # Use Physical Pin Numbering Scheme
button1=16                 # Button 1 is connected to physical pin 16
button2=12                 # Button 2 is connected to physical pin 12
LED1=22                    # LED 1 is connected to physical pin 22
LED2=18                    # LED 2 is connected to physical pin 18
GPIO.setup(button1,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Make button1 an input, Activate Pull UP Resistor
GPIO.setup(button2,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Make button 2 an input, Activate Pull Up Resistor
GPIO.setup(LED1,GPIO.OUT,) # Make LED 1 an Output
GPIO.setup(LED2,GPIO.OUT)  # Make LED 2 an Output
BS1=False                  # Set Flag BS1 to indicate LED is initially off
BS2=False                  # Set Flag BS2 to indicate LED is initially off
while(1):                  # Create an infinite Loop
        if GPIO.input(button1)==0:            # Look for button 1 press
                print "Button 1 Was Pressed:"
                if BS1==False:                # If the LED is off
                        GPIO.output(LED1,True)# turn it on
                        BS1=True              # Set Flag to show LED1 is now On 
                        sleep(.5)             # Delay
                else:                         # If the LED is on
                        GPIO.output(LED1,False) # Turn LED off
                        BS1=False               # Set Flag to show LED1 is now Off
                        sleep(.5)
        if GPIO.input(button2)==0: #Repeat above for LED 2 and button 2
                print "Button 2 Was Pressed:"
                if BS2==False:
                        GPIO.output(LED2,True)
                        BS2=True
                        sleep(.5)
                else:
                        GPIO.output(LED2,False)
                        BS2=False
                        sleep(.5)

from time import sleep # Import sleep Library

import RPi.GPIO as GPIO # Import GPIO Library

GPIO.setmode(GPIO.BOARD) # Use Physical Pin Numbering Scheme

button1=16 # Button 1 is connected to physical pin 16

button2=12 # Button 2 is connected to physical pin 12

LED1=22 # LED 1 is connected to physical pin 22

LED2=18 # LED 2 is connected to physical pin 18

GPIO.setup(button1,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Make button1 an input, Activate Pull UP Resistor

GPIO.setup(button2,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Make button 2 an input, Activate Pull Up Resistor

GPIO.setup(LED1,GPIO.OUT,) # Make LED 1 an Output

GPIO.setup(LED2,GPIO.OUT) # Make LED 2 an Output

BS1=False # Set Flag BS1 to indicate LED is initially off

BS2=False # Set Flag BS2 to indicate LED is initially off

while(1): # Create an infinite Loop

if GPIO.input(button1)==0: # Look for button 1 press

print "Button 1 Was Pressed:"

if BS1==False: # If the LED is off

GPIO.output(LED1,True)# turn it on

BS1=True # Set Flag to show LED1 is now On

sleep(.5) # Delay

else: # If the LED is on

GPIO.output(LED1,False) # Turn LED off

BS1=False # Set Flag to show LED1 is now Off

sleep(.5)

if GPIO.input(button2)==0: #Repeat above for LED 2 and button 2

print "Button 2 Was Pressed:"

if BS2==False:

GPIO.output(LED2,True)

BS2=True

sleep(.5)

else:

GPIO.output(LED2,False)

BS2=False

sleep(.5)

We are now ready to learn how to “read” values from the Raspberry Pi GPIO pins. In order to demonstrate this, we will show a simple example using buttons. If you ordered the Raspberry Pi kit we recommend, you already have everything you need, or you can pick your kit up HERE. To start with, you need to put together a simple circuit that connects two push buttons to your Raspberry Pi. Connect according to this schematic.

Raspberry Pi Buttons — Simple Circuit Connecting Two Push Buttons to the Raspberry Pi

Note that one leg of each button is connected to the ground rail on the breadboard, that is connected to the Pi ground at physical pin 6. Then we connect the left leg of the left button to physical pin 16, and the left leg of the right button to physical pin 12.

In order to read the state of these buttons, that is, whether they are being pressed or not, we need to write a python program. To begin with we must import GPIO library and specify that we want to

from time import sleep     # Import time library
import RPi.GPIO as GPIO    # Import RPi Library
GPIO.setmode(GPIO.BOARD)   # Specify We Want to reference Physical pins

from time import sleep # Import time library

import RPi.GPIO as GPIO # Import RPi Library

GPIO.setmode(GPIO.BOARD) # Specify We Want to reference Physical pins

Now we are ready to set the pin modes on the pins we are using. We are using pins 12 and 16. We will set up variables so that we can reference the pins by descriptive variables.

button1=16  # Descriptive Variable for pin 16
button2=12  # Descriptive Variable for pin 12
GPIO.setup(button1,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Set button1 as input and Activate pull up resistor
GPIO.setup(button2,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Set button2 as input and Activate pull up resisor

button1=16 # Descriptive Variable for pin 16

button2=12 # Descriptive Variable for pin 12

GPIO.setup(button1,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Set button1 as input and Activate pull up resistor

GPIO.setup(button2,GPIO.IN,pull_up_down=GPIO.PUD_UP) # Set button2 as input and Activate pull up resisor

Note in our GPIO.setup commands, we are not just defining the pins as inputs, we are also activating pullup resistors with

pull_up_down=GPIO.PUD_UP

1	pull_up_down=GPIO.PUD_UP

With this command, the raspberry pi places a pullup resistor between the designated pin and the 3.3 V rail. This means that if we simply read the pin, we will read a “1”, “True”, or “High”, since the pin will see the rail through the pullup resistor. If we connect the pin to ground by pressing a button or switch, the pin will then read a “0”, “False” or “Low” because it will be a straight connection to ground, and as current flows through the pullup resistor, the 3.3 Volts will drop across the pullup resistor. Hence, the pin sees 0 volts.

The result is that with the pullup resistor activated, the pin will always report a “1” until something connects the pin to ground, and then it will read a “0”. This configuration should work for most things, but if you are getting unpredictable results which can result from electrical noise, then try using external pullup resistors.

Now we are ready to read the values from the pins.

while(1): # Create an infinite loop

        if GPIO.input(button1)==0: # button1 will report 0 if it is pressed
                print "Button 1 Pressed"
                sleep(.1)   # delay
        if  GPIO.input(button2)==0: # button 2 will report 0 if it is presses
                sleep(.1)
                print "Button 2 Pressed"

while(1): # Create an infinite loop

if GPIO.input(button1)==0: # button1 will report 0 if it is pressed

print "Button 1 Pressed"

sleep(.1) # delay

if GPIO.input(button2)==0: # button 2 will report 0 if it is presses

sleep(.1)

print "Button 2 Pressed"

Notice that we read from the pin using the GPIO.input command. Also note that for reliable results you need to usually put a small delay in your code. This will help debounce the button, and will also give more stable results.

OK, so our final code is as follows:

from time import sleep
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
button1=16
button2=12
GPIO.setup(button1,GPIO.IN,pull_up_down=GPIO.PUD_UP)
GPIO.setup(button2,GPIO.IN,pull_up_down=GPIO.PUD_UP)
while(1):
        if GPIO.input(button1)==0:
                print "Button 1 Pressed"
                sleep(.1)
        if  GPIO.input(button2)==0:
                sleep(.1)
                print "Button 2 Pressed"

from time import sleep

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BOARD)

button1=16

button2=12

GPIO.setup(button1,GPIO.IN,pull_up_down=GPIO.PUD_UP)

GPIO.setup(button2,GPIO.IN,pull_up_down=GPIO.PUD_UP)

while(1):

if GPIO.input(button1)==0:

print "Button 1 Pressed"

sleep(.1)

if GPIO.input(button2)==0:

sleep(.1)

print "Button 2 Pressed"

This code will sit and monitor the buttons, and when one is pressed it will report that that button has been pressed.

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Technology Tutorials

Tag Archives: Push Buttons

Raspberry Pi LESSON 30: Controlling LEDs from Push Buttons

Raspberry Pi LESSON 29: Configuring GPIO Pins as Inputs

Making The World a Better Place One High Tech Project at a Time. Enjoy!