04 Arduino Peripheral Interfacing

Temperature sensors
0 Gives a Vout propotional to ambient room
temperature.

0 Concept : as temperature increases, voltage
across a p-n junction increases at a known
rate. (in this case Vbe)

0 Voltage at Anlg.Pin in Volts = (reading
from ADC) * (5/1024) V
0 Centigrade temperature = [(analog voltage
in V) – 0.5] * 100

Before: Writing the code
0 Review:
0 How does the lm35 work?
0 Read datasheet of lm35.
0 How to connect it to arduino?
0 What reference to use?
0 What sort of noises will be present?
0 What does the analogue input signify?

Temp sensor code
0 Connect lm35 as per circuit diagram in 7. Temp Sensor
folder.

0 We’re giving AREF as 3.3V to reduce noise from the
LM35 and give more accurate readings.

0 Upload code onto Arduino and Output is seen in the
Serial monitor of the Arduino.

Write the code
1. Decide which analogue pin you’re going to and
assign it to a global variable
2. in setup() { }, initialize serial port to 9600 baud rate
to send temp reading out to PC.
3. In loop() { }, take the analogue reading from a pin
and store it in a temp float variable.
4. Multiply reading by 5.0 and then divide by 1024 to
get voltage value read by the port. Store this is a
float variable called volt.
5. Print out this value to the serial port and check.

Keep Writing the code
0 To get temp in centigrade, (volt – 0.5) * 100

0 This is the ambient temperature recognized by the
LM35 in Celsius.

0 Send it to the serial port and check your code.

0 To convert to fahrenheight, mult by 9 then divide by 5
then add 32 to that result. Send it to serial port too.

0 Congratulate yourself please.

Improvements?
0 Use 3.3V as reference to increase resolution since
datasheet says that resolution of lm35 ~ 10mV.

0 Put in on PCB to avoid noise by breadboard internal
resistance,

0 DO NOT LIGHT THE LM35 OR IMMERSE IT IN WATER.

0 Make a waterproof casing for the lm35 to test temp of
liquids.

0 Any other applications?

LDR
0 An LDR is a Light Dependent Resistor.
0 As in the resistance offered by this device to an
electrical circuit is dependent on the amount of light
falling on the circuit.

0 Also called photocells because they convert light
energy to an electrical response.

0 Useful for on-when-light/off-when-dark.

How to connect the LDR
0 LDR is basically a resistor, so it can be connected
anyway.

0 You need a pull-down resistor to avoid sinking all the
current onto the arduino pin.

0 Circuit is GND-10kohn-LDR-VCC.

0 This circuit will only work if between 0-5V. If light is
too bright, it will saturate at 5V.
0 putting a variable resistor in place of 10k allows for
controlling saturation with too bright/too dark light.

Photocell Current
Ambient Ambient LDR + R Voltage
resistance thru LDR
light like… light (lux) (Ω) across R
(Ω) +R
Dim
0.1 lux 600KΩ 610 KΩ 0.008 mA 0.1 V
hallway
Moonlit
1 lux 70 KΩ 80 KΩ 0.07 mA 0.6 V
night
Room 10 lux 10 KΩ 20 KΩ 0.25 mA 2.5 V
Dark
overcast
day / 100 lux 1.5 KΩ 11.5 KΩ 0.43 mA 4.3 V
Bright
room
Overcast
1000 lux 300 Ω 10.03 KΩ 0.5 mA 5V
day

Writing code!
0 decide analoge pin used as input to LDR.

0 In setup(){ }, initialize serial port with 9600.

0 In loop(){ }, first do an analogueread(pin) and store it in an
int variable called reading.

0 This value represents illumination received by LDR.
0 Send it to Serial Port.

0 Allow delay of some time to let the ADC settle.

Application 1
0 Make thresholds and determine the brightness
received and send it via serial port.

if (reading < 10) { Serial.println(" - Dark"); }
else if (reading < 200) { Serial.println(" - Dim"); }
else if (reading < 500) { Serial.println(" - Light"); }
else if (reading < 800) { Serial.println(" - Bright"); }
else { Serial.println(" - Very bright"); }

Application 2
0 Take the analogue reading and use it as the delay
amount in an LED blinking scenario. Use ledpin = 13.

void loop()
{
val = analogRead(LDR);
digitalWrite(ledPin, HIGH);
delay(val);
digitalWrite(ledPin, LOW);
delay(val);
}

Another Application
0 Put three LEDs around the LDR. Red, Green and Blue.

0 Put an object of a particular color in front of the LDR.

0 Light up RED LED and measure LDR value
0 Light up GREEN LED and measure LDR value
0 Light up BLUE LED and measure LDR value

0 From these three analogue values you can determine the
color of object being sensed.

Sensor Data on PC
0 Reading and plotting sensor data on PC is very simple
on the arduino.

0 Send data continuously to the computer over the
serial port.

0 Data can be viewed by any program capable of
viewing this data

Send sensor data to serial
port
0 Open the folder Sensor data graph

0 Upload the arduino code onto the arduino and close
arduino IDE after checking serial monitor.

0 In softwares folder extract the processing folder.

0 Open processing and copy the processing code onto it and
run.

0 Make sure serial port number in the processing sketch
matches arduino

The motor shield
The motor shield goes on top
1. DC Motor Interface of the arduino neatly.
Drives 2 motors with L293D DC Motor
Driver IC.
There are loads of shields for
the arduino that provide
2. IR paired sensors
different functionality.
For line sensing, 4 IR sensor pairs can be
attached and controlled.
Be careful removing the
shield, if you bend the pins,
3. The Buzzer or Servo Motor
you cant put the shield in
Selectable via jumper
again.
4. The Switch or Servo Motor
Selectable via jumper

5. Two LEDs

IR TX RX Pair
0 An IR transmitter (TX) is a LED that emits
light in the infrared spectrum.
0 (most cameras see IR, light up the IR LED
and point a camera at it to check)

0 An IR Receiver (RX) is a transistor with the
base exposed.
0 The base voltage depends on the amount of
IR received and it controls the amount of
current passing through the C-E junction
(leads).

IR schematic
0 The IR TX LED is connected through a current
limiting resisto
0 The IR RX is connected via a variable potentiometer
to a voltage comparator to give a digital output.

0 The pot is used to adjust
For ambient light intensity.

Remember
0 The IR TX RX pairs should be spaced 1/4th of an inch apart
for optimal detection.

0 Calibration of IR sensors is important to adjust the sensors
for ambient light.

0 The output of this circuit is DIGITAL and read by a digital
pin. 1 – obstruction; 0 – No obstruction.

0 If you have to use IR sensors in the sun, use electrical tape
to provide adequate shielding.

Using the IR sensors
0 The motor shield has 4 IR sensors and 4 pots.
0 Connect the IR dongles to the placeholders. They go in only
one way
0 There are status LEDs just next to each IR socket, if the
comparator goes HIGH, the LED lights. This is for
calibration.
0 Keep the IR sensor pointed at nothing (no obstruction).
0 Use a screwdriver and GENTLY turn the appropriate POT
until the respective IR sensors status LED turns dark.
0 Check with your hand if LED lights, if not readjust as you
like.

PINS
0 The table below shows the pin arrangement for the 4
sensors on the shield.

0 If the shield is mounted, then these 4 pins provide the
output of the comparator.

0 Use digitalread(pin) to see the state of the pin at any
time.

Try
0 Connect all four IR sensors and calibrate them.

0 Write a program to output which of the 4 IR sensors
has gone HIGH to the serial port.

0 CHALLENGE: Try and make sure that the message on
the serial port doesn’t repeat until the IR sensor has
gone LOW again (obstruction removed). It shouldn't
continuously output the message if the IR sensor is
obstructed,

DC motors
0 Motors are devices that convert electrical energy to
mechanical energy.

0 Motors come in different varieties: AC, DC, Servo, Stepper
etc

0 If motor draws less than 40mA of current, it can be directlu
wired to an arduino pin.

0 Current drawn by a DC motor is propotional to speed and
torque. To avoid burning out the arduino, we use motor
drivers to control DC motors.

The L293 driver
0 This chip isolates logic level voltages and the motor supply
voltages.

0 It as also called a H-bridge.

0 It uses the transistors as a switch concept to electrically
switch a DC power supply onto the terminals of the motor.

0 The driver can control two motors independently from the
same supply.

The Motor Shield
0 The motor driver is present on the
shield which also contains a wire
block for easy connection of the
wires.

0 The supply will have terminals
marked on the board. Do not reverse -
these connections. +

0 Motor can be connected in anyway.
The direction might have to be
calibrated by testing if the terminals
are reversed.

Arduino shield to Motor
Driver Pinout
0 To use a motor, set the enable pin to high in the setup() { }

0 Motor movement is done in loop() { }
0 If l1 is HIGH and l2 is LOW, motor turn in one direction.
0 If l1 is LOW and l2 is HIGH, the motor turns in the other
direction.

0 If both l1 and l2 are set to HIGH or LOW, then motor is stopped.

Wiring motors
0 Attach the arduino shield onto the arduino.

0 Take a 9V battery cap and screw it onto the motor
supply terminals. Take care of polarity.
0 Red >> + and Black >> -

0 Wire up the motors and connect them to the
terminals.

TRY
0 Move both motors in same direction.

0 Reverse both motors.

0 Stop one and turn the other.
0 Stop the other and turn the one.

0 Make each motor turn in a different direction.

Exercise
0 Combine the functionality of 2 IR sensors and the
motors to make an obstacle avoider bot.

0 Algorith:
0 Move forward, left and right randomly.
0 If IR sensors detect an obstruction, move a little back in
the opposite side of the obstruction
0 Continue.

04 Arduino Peripheral Interfacing

More Related Content

What's hot

Viewers also liked

Similar to 04 Arduino Peripheral Interfacing

More from Wingston

Recently uploaded

04 Arduino Peripheral Interfacing