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;lIR:-

MQ:-

RELAY:-

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DIGITAL INPUTS

Digital inputs can be define as that which inputs those having in digital

signal condition i.e. high or low, either Vs or VE on other hand in binary

form 1 or 0 these types of signal are known as digital inputs signals. These

digital inputs are provide by digital sensor modules or switches.

Here we use for digital inputs some switches and IR sensor digi ta lmodu lewhich gives us a digital inputs to the controlling part of this project

IR Module

In this tutorial we will see how to make simple infrared sensor module for

detecting reflecting surface. This sensor can be used to detect reflecting

silver/white strip, obstacle detection, flame detection, etc. These sensors

are primary requirement of any simple line follower robocar.

WORKING OF IR SENSORS

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IR LED emits infrared radiation. This radiation illuminates the surface in

front of LED. Surface reflects the infrared light. Depending on reflectivity of

the surface, amount of light reflected varies. This reflected light is made

incident on reverse biased IR sensor. When photons are incident on

reverse biased junction of this diode, electron-hole pairs are generated,

which results in reverse leakage current. Amount of electron-hole pairs

generated depends on intensity of incident IR radiation. More intense

radiation results in more reverse leakage current. This current can be

passed through a resistor so as to get proportional voltage. Thus as

intensity of incident rays varies, voltage across resistor will vary

accordingly.

This voltage can then be given to OPAMP based comparator. Output of the

comparator can be read.

IR LED is used as a source of infrared rays. It comes in two packages 3mm

or 5mm. 3mm is better as it is requires less space. IR sensor is nothing but

a diode, which is sensitive for infrared radiation. This infrared transmitter

and receiver is called as IR TX-RX pair. It can be obtained from any

decent electronics component shop and costs less than 10Rs. Following

snap shows 3mm and 5mm IR pairs. Colour of IR transmitter and receiver

is different. However you may come across pairs which appear exactly

same or even has opposite colours than shown in above pic and it is not

possible to distinguish between TX and RX visually. In case you will have

to take help of multimeter to distinguish between them

The IR LED is just like any other LED, in that a current-limiting resistor is

useful to control the device current and therefore the light intensity. With a

100 ohm resistor and the approximately 1.5V forward voltage drop of the IR

LED, we'll have a LED current of about 35mA. That's fairly high, but more

light emitted will yield more light coming back to our sensor.

The phototransistor is a device with an exposed silicon junction. When light

passes through the plastic casing, most non-IR wavelengths are simply

absorbed by the plastic, but the infrared light makes it to the sensor within.

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Each photon striking the silicon junction causes an electron to flow.

Because this is a phototransistor and not a photodiode, this current is

multiplied by the transistor's current gain, so each photon may actually

cause perhaps 10 to 100 electrons to flow. This current has nowhere to go

except through the 10K resistor, and as the current passes through the

resistor, the voltage across the resistor rises (V=IR). This change in voltage

is read by our microcontroller's Analog to Digital Converter (ADC).

MQ5 (LPG DETECTOR SESNOR)

LM358

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FEATURES

High sensitivity to LPG, iso-butane, propane

Small sensitivity to alcohol, smoke.

* Fast response . * Stable and long life * Simple drivecircuit

APPLICATION

They are used in gas leakage detecting equipments in family

and industry, are suitable for detecting of LPG, iso-butane,

propane, LNG, avoid the noise of alcohol and cooking fumes and

cigarette smoke.

Structure and configuration of MQ-6 gas sensor is (Configuration

A or B), sensor composed by micro AL2O3 ceramic tube, Tin

Dioxide (SnO2) sensitive layer, measuring electrode and heater

are fixed into a crust made by plastic and stainless steel

net. The heater provides necessary work conditions for work

of sensitive components. The enveloped MQ-6 have 6 pin ,4 ofthem are used to fetch signals, and other 2 are used for providing

heating current.

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12V RELAY

A relay is a switch which is

operated by electricity.

It is usually electromagnetic

device which has coil.

When this coil is supplied with

power, a magnetic field

created and will operate

mechanical switch.

There are solid state relays

which do not have moving

parts but are very expensive

compared to small

mechanical relays. Pictures in

this page shows typical small

electro mechanical relay.

Relay is used when we need

to handle high voltages and

currents through

microcontroller operated

system.

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A relay is a switch which is operated by electricity. It is usually electromagnetic device whichhas coil. When this coil is supplied with power, a magnetic field created and will operate

mechanical switch. There are solid state relays which do not have moving parts but are veryexpensive compared to small mechanical relays. Pictures in this page shows typical small electro

mechanical relay. Relay is used when we need to handle high voltages and currents through

microcontroller operated system.

elay coil's current requirement is usually more than 100mA (for small relay about 100mA) and

microcontroller cant supply this much of current to relay by it self. So as shown in followingschematic diagram, we have to use transistor to handle this current requirement. Base pin of

NPN transistor used here is connected to ground pin via resistor to make sure that relay will stayoff when microcontroller does not output +5V to transistors base. This will make sure only logic

1 on microcontroller pin will activate relay. It is better to use Darlington transistor to handlecurrent requirement for relay, because darlington transistor can handle more current than single

transistor.

It is essential to connect a diode across relay coil in reverse bias to protect transistor form back

EMF created when relay is released from energized or ON state. If this diode is not used,

transistor and/or microcontroller which is driving relay may be damaged upon releasingenergized relay. The diode will short out the back EMF produced by coil when it turned OFF

from ON state.

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Transistor

The BC548 is a general purposeepitaxialsiliconNPNbipolar junction transistorfound commonly in

European electronic equipment. The part number is assigned byPro Electron, which allows many

manufacturers to offer electrically and physically interchangeable parts under one identification. The

BC548 is commonly available in European Union countries. It is often the first type of bipolar transistor

young hobbyists encounter, and is often featured in circuit diagrams and designs published

http://en.wikipedia.org/wiki/Epitaxyhttp://en.wikipedia.org/wiki/Epitaxyhttp://en.wikipedia.org/wiki/Epitaxyhttp://en.wikipedia.org/wiki/NPN_transistorhttp://en.wikipedia.org/wiki/NPN_transistorhttp://en.wikipedia.org/wiki/Bipolar_junction_transistorhttp://en.wikipedia.org/wiki/Bipolar_junction_transistorhttp://en.wikipedia.org/wiki/Bipolar_junction_transistorhttp://en.wikipedia.org/wiki/Pro_Electronhttp://en.wikipedia.org/wiki/Pro_Electronhttp://en.wikipedia.org/wiki/Pro_Electronhttp://en.wikipedia.org/wiki/Pro_Electronhttp://en.wikipedia.org/wiki/Bipolar_junction_transistorhttp://en.wikipedia.org/wiki/NPN_transistorhttp://en.wikipedia.org/wiki/Epitaxy

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