Electricity Resistors Bread boardSwitches MP3 Player

Module 4

Electricity & Current

Powerful pump

Force of water is too much for the wheel

It breaks!

Add artificial resistance in the pipe

Protects the wheel

Electricity & Current

Electricity & Current

Power Source (high voltage)

Ground (zero voltage)

Resistor (560 Ohms)

LED

Electricity & CurrentFlow of current

Remember:

Current flows from high voltage (3.3V) to low voltage (zero V aka Ground)

Why Bread Boards?

No need to solder simple circuits by hand

Easy to prototype

Bread BoardThis is one connected

wire

Signs don’t really mean anything

Convention:

Connect the power source to the red + connector

Connect GND to the blue - connector

Bread Board

(a)

(b)

(c)

How are the three wires connected?

Bread Board

(a)

(b)

(c)

correct

How are the three wires connected?

Electricity & Current

Raspberry Pi GPIO pinsGeneral Purpose Input Output pins

Can connect any input or output device to each pin

e.g., motors, motion sensors, light sensors, etc.

PI CobblerGPIO pins are not labelled on the R-Pi

Need to get the correct jumper wires

Annoying to read up the number and connect on bread board

Pi-Cobbler

Program GPIO pins>>> import Rpi.GPIO as gpio>>> gpio.setmode(gpio.BCM)>>> gpio.setup(18, gpio.IN)>>> print(gpio.input(18))

Switch ConceptSwitch Off Switch On

if gpio.input(18) == gpio.LOW

if gpio.input(18) == gpio.HIGH

Switch ConceptWon’t Work!

When switch is off, pin 18 is in “floating” state

It will not give reliable reading

Sometimes it will be gpio.HIGH, sometimes gpio.LOW

Somehow connect pin 18 to GND when switch is on or off

Switch Pull-Up Circuit

Switch Pull-Up CircuitSwitch Off Switch On

if gpio.input(18) == gpio.HIGH

if gpio.input(18) == gpio.LOW

Switch Pull Up Circuitimport RPi.GPIO as gpio

gpio.setmode(gpio.BCM)gpio.setup(18, gpio.IN)

while True:if gpio.input(18) == gpio.LOW:

print('************* SWITCH ON')

elif gpio.input(18) == gpio.HIGH:print('------------ SWITCH

OFF')

Switch Pull Up Circuit

Computer is checking the while condition around 2000 times per second!

We are actually only interested in the state change from on off or from off on

Switch Pull Up Circuit

Refer to https://bitbucket.org/avilay/raspberry_pyrates/src/master/switch_simple.py

PhotocellIt is a resistor whose resistance changes with light

In light less resistance more current can pass through it

In dark very high resistance no current can pass through

Photocell as Switch

Photocell as SwitchIn Dark In Light

if gpio.input(18) == gpio.HIGH

if gpio.input(18) == gpio.LOW

Photocell as Switch

Refer to https://bitbucket.org/avilay/raspberry_pyrates/src/master/photocell.py

MP3 Player

def handle_state_change(curr_switch_state):os.system('espeak "Changing track."')time.sleep(2)if curr_switch_state == 'LIGHT':

os.system('mpg123 /home/pi/viva.mp3 &')elif curr_switch_state == 'DARK':

os.system('mpg123 /home/pi/waiting.mp3 &')

Electricity Resistors Bread boardSwitches MP3 PlayerGot It!!

Module 4

LEDsSensors Cool Projects

Module 4

What do you want to do next?

Controlling LED

Controlling LEDimport timeimport RPi.GPIO as gpio

gpio.setmode(gpio.BCM)gpio.setup(22, gpio.OUT)

gpio.output(22, gpio.HIGH)time.sleep(5)gpio.cleanup()

Note: Using pin 22 as an OUTPUT pin this time

Blinking LED

Refer to https://bitbucket.org/avilay/raspberry_pyrates/src/master/led_blink.py

Some Sensors to Play WithDC Motor – spins anything connected to it, like a wheel

Temperature sensor – measures the temperature of the environment

Vibration sensor – detects vibration to whatever it is attached to

Some Sensors to Play WithDC Motor – spins anything connected to it, like a wheel

Camera board