raspberry pi led

1. LED BLINKING
Raspberry Pi

3. GPIO
 A powerful feature of the Raspberry Pi is the row
of GPIO (general-purpose input/output) pins
along the top edge of the board. A 40-pin GPIO
header is found on all current Raspberry Pi
boards (unpopulated on Pi Zero and Pi Zero W).
Prior to the Pi 1 Model B+ (2014), boards
comprised a shorter 26-pin header.

5. There are two kinds of Input and Output pin
numbering for the Raspberry pi. One is the BCM and
the other is BOARD. Basically these pin numberings
are useful for writing python script for the Raspberry
Pi.

6. GPIO BOARD
This type of pin numbering refers to the number
of the pin in the plug, i.e, the numbers printed on
the board, for example, P1. The advantage of this
type of numbering is, it will not change even
though the version of board changes.

7. GPIO BCM
 The BCM option refers to the pin by “Broadcom
SOC Channel. They signify the Broadcom SOC
channel designation. The BCM channel changes
as the version number changes.
 Note: It is very important to wire the GPIO pins
with limited resistors to avoid serious damage to
the Raspberry Pi. LEDs must have resistors to
limit the current passing through them. The
motors should not be connected to the GPIO pins
directl

8. What is the difference between BOARD and BCM for GPIO
pin numbering?
 The GPIO.BOARD option specifies that you are referring to the pins by
the number of the pin the the plug - i.e the numbers printed on the board
(e.g. P1) and in the middle of the diagrams below.
 The GPIO.BCM option means that you are referring to the pins by the
"Broadcom SOC channel" number, these are the numbers after "GPIO"
in the green rectangles around the outside of the below diagrams:

9. Identification of the pin numberings via
Linux command
 There is a Linux command to find out which name is
for which GPIO pin. So in that case, we do not have
to worry about a tutorial to have by our side to check
out the pin numberings of the Raspberry Pi all the
time.
 Type the following command in the terminal,
pinout

10. How to use the GPIO pin numbers in
Python?
 simple LED blink python program with Raspberry
Pi. The number 11 is the pin for LED and
considered as an output.
import RPi.GPIO as GPIO
from time import sleep
GPIO.setmode (GPIO.BOARD)
GPIO.setup (11,GPIO.OUT)
while True:
GPIO.output(11,True)
time.sleep(2)
GPIO.output(11,False)
time.sleep(2)

11. How to make an LED blink with
Raspberry Pi?
Things you need
 Breadboard
 Light Emitting Diode
 Resistor > 68 ohms
 Raspberry Pi
 wires

12. Circuit Diagram

13. Procedure
 Insert an LED into a breadboard.
 Connect the resistor which is more than 68 ohms
across the longer end of the LED.
 Connect the GPIO pin 11 to the shorter end of the
LED.
 Connect the GPIO pin 6 (ground) to the other end
of the resistor.

14. import RPi.GPIO as GPIO
from time import sleep
 The two lines above from the code explains,
importing the libraries you will need RPi.GPIO to
control the GPIO pins. Importing time to control
how long the pin will be ON or OFF.

15. GPIO.setmode (GPIO.BOARD)
GPIO.setup (11,GPIO.OUT)
 GPIO.BOARD indicates the numbering scheme
you are using. The line (11,GPIO.OUT) means
you are using GPIO pin 11 as output pin.

16. while True:
GPIO.output(11,True)
time.sleep(2)
GPIO.output(11,False)
time.sleep(2)
 while is used to continue as long as the program
runs.
GPIO.output(11,True) sets the output to high and
remain that way for 2 seconds ( sleep(2)). The same
is set to low and remain that way for 2 seconds. If
you need time-lapse for 5 seconds, you can change
that in time.sleep(5).

19. LED BLINK with switch

20.  import RPi.GPIO as GPIO
 #GPIO.setwarnings(False)
 GPIO.setmode(GPIO.BCM)
 GPIO.setup(4,GPIO.OUT)
 GPIO.setup(3,GPIO.IN,pull_up_down=GPIO.PUD
_UP)
 while True:
 i=GPIO.input(3)
 if i==True:
 GPIO.output(4,True)
 else:
 GPIO.output(4,False)


21. Build a simple app that interacts with
Raspberry Pi GPIO. using three LEDs, which
are attached to the Raspberry Pi board.
Furthermore, turn the LEDs on/off
sequentially.
The following hardware components are needed:
 Raspberry Pi
 Three LEDs of any color
 Three resistors (330 Ω or 220 Ω)

22.  LED 1 is connected to Pi GPIO18
LED 2 is connected to Pi GPIO23
LED 3 is connected to Pi GPIO24

23. We can write a program using WiringPi with Python.
The following is the complete Python code for blinking
LEDs:
import wiringpi2 as wiringpi
import time
# initialize
wiringpi.wiringPiSetup()
# define GPIO mode
GPIO18 = 1
GPIO23 = 4
GPIO24 = 5

24. LOW = 0
HIGH = 1
OUTPUT = 1
wiringpi.pinMode(GPIO18,
OUTPUT)
wiringpi.pinMode(GPIO23,
OUTPUT)
wiringpi.pinMode(GPIO24,
OUTPUT)
# make all LEDs off
def clear_all():
wiringpi.digitalWrite(GPIO18, LOW)
wiringpi.digitalWrite(GPIO23, LOW)
wiringpi.digitalWrite(GPIO24, LOW)
try:
while 1:
clear_all()
print("turn on LED 1")
wiringpi.digitalWrite(GPIO18, HIGH)
time.sleep(2)
clear_all()
print("turn on LED 2")
wiringpi.digitalWrite(GPIO23,
HIGH)
time.sleep(2)
clear_all()
print("turn on LED 3")
wiringpi.digitalWrite(GPIO24,
HIGH)
time.sleep(2)
except KeyboardInterrupt:
clear_all()
print("done")

25. three LED operation with single
switch

26. import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(4,GPIO.OUT)
GPIO.setup(17,GPIO.OUT)
GPIO.setup(27,GPIO.OUT)
GPIO.setup(3,GPIO.IN,pull_up_down=GPIO.PUD_UP)
x=0
y=0
while True:
i=GPIO.input(3)
print("i=",i)
if i==True:
x=x+1

27. print("x=",x)
if x==1:
y=y+1
print("y=",y)
if y==4:
y=1
if y==1:
GPIO.output(4,True)
GPIO.output(17,False)
GPIO.output(27,False)
elif y==2:
GPIO.output(4,False)
GPIO.output(17,True)
GPIO.output(27,False)
elif y==3:
GPIO.output(4,False)
GPIO.output(17,False)
GPIO.output(27,True)
else:
x=0

28. import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(19,GPIO.OUT)
while True:
GPIO.output(19,GPIO.HIGH)
time.sleep(1)
GPIO.output(19,GPIO.LOW)
time.sleep(1)

29.  https://create.withcode.uk/python/A3

30. DHT11 Temperature and Humidity Sensor and the
Raspberry Pi
 DHT11 is a low-cost temperature and humidity
sensor. It isn’t the fastest sensor around but its cheap
price makes it useful for experimenting or projects
where you don’t require new readings multiple times a
second. The device only requires three connections to
the Pi. +3.3v, ground and one GPIO pin.

31. DHT11 Specifications
 The device itself has four pins but one of these is
not used. You can buy the 4-pin device on its own
or as part of a 3-pin module.

The modules have three pins and are easy to connect directly to the Pi’s
GPIO header.
Humidity : 20-80% (5% accuracy)
Temperature : 0-50°C (±2°C accuracy)
The manufacturers do not recommended that you read data from this
device more than once per 2 seconds. If you do you may get incorrect

32. Hardware Setup
 The 4-pin device will require a resistor (4.7K-10K) to be placed
between Pin 1 (3.3V) and Pin 2 (Data).
 The 3-pin modules will usually have this resistor included which
makes the wiring a bit easier. For this reason I got hold of the
module which I could then attach to the Pi with a piece of 3-way
cable.
 Different suppliers may wire the module pins differently so check
the PCB markings to identify Vcc (+), data and Ground (-).
 The 3 pins should be connected to the Pi as shown in the table
below :DHT Pin Signal Pi Pin
1 3.3V 1
2 Data/Out 11 (GPIO17)
3 not used –
4 Ground 6 or 9

33. Your data pin can be attached to any GPIO pin you prefer. In my example I
am using physical pin 11 which is GPIO 17. Here is a 4-pin sensor
connected to the Pi’s GPIO header. It has a 10K resistor between pin 1
(3.3V) and 2 (Data/Out).

34. Python Library
 The DHT11 requires a specific protocol to be
applied to the data pin. In order to save time
trying to implement this yourself it’s far easier to
use the Adafruit DHT library.
 The library deals with the data that needs to be
exchanged with the sensor but it is sensitive to
timing issues. The Pi’s operating system may get
in the way while performing other tasks so to
compensate for this the library requests a number
of readings from the device until it gets one that is
valid.

35. Software Setup
To start with update your package lists and install a few
Python libraries :
sudo apt-get update
sudo apt-get install build-essential python-dev
Then clone the Adafruit library from their repository :
git clone https://github.com/adafruit/Adafruit_Python_DHT.git
cd Adafruit_Python_DHT
Then install the library for Python 3 :
sudo python3 setup.py install

36. Adafruit Example Python Script
Adafruit provide an example script that you can use to
check your sensor is operating correctly.
cd ~
cd Adafruit_Python_DHT
cd exemples
Then :
python AdafruitDHT.py 11 17
The example script takes two parameters. The first is the sensor type so is
set to “11” to represent the DHT11. The second is the GPIO number so
for example using “17” for GPIO17. You can change this if you are using
a different GPIO pin for your data/out wire.
You should see an output similar to this :
Temp=22.0* Humidity=68.0%

37. Using the Library In Other Python Scripts
import Adafruit_DHT
# Set sensor type : Options are DHT11,DHT22 or AM2302
sensor=Adafruit_DHT.DHT11
# Set GPIO sensor is connected to
gpio=17
# Use read_retry method. This will retry up to 15 times to
# get a sensor reading (waiting 2 seconds between each retry).
humidity, temperature = Adafruit_DHT.read_retry(sensor, gpio)
# Reading the DHT11 is very sensitive to timings and occasionally
# the Pi might fail to get a valid reading. So check if readings are valid.
if humidity is not None and temperature is not None:
print('Temp={0:0.1f}*C Humidity={1:0.1f}%'.format(temperature, humidity))
else:
print('Failed to get reading. Try again!')