MOBILE Control Electrical

8/3/2019 MOBILE Control Electrical

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MOBILE

CONTROL ELECTRICALAPPLIANCES


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Project Introduction.

This unit talks about the basic definitions needed to understand the

Project better and further defines the technical criteria to be

implemented as a part of this project.

Why automation?

Earlier, we are looking into the face of future when we talked about automated

devices, which could do anything on instigation of a controller, but today it has

become a reality.

1. An automated device can replace good amount of human working force,

moreover humans are more prone to errors and in intensive conditions the

probability of error increases. Whereas an automated device can work with

diligence, versatility and with almost zero error.

2. This is why this project looks into construction and implementation of a system

involving hardware to control a variety of electrical and electronics instruments.

What is home/office automation?

Home/office automation is the control of any or all electrical devices in our home

or office, whether we are there or away. Home/office automation is one of the

most exciting developments in technology for the home that has come along in

decades. There are hundreds of products available today that allow us control


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over the devices automatically, either by remote control; or even by voice

command!

What can be automated?

Virtually anything in the home/office that is powered by electricity can be

automated and/or controlled. We can control our electrical devices with our

cordless phone from our easy chair. We can turn our porch lights on

automatically at dark or when someone approaches and can see who is at the

front door from any nearby television, and talk to them or unlock the door from

any nearby telephone. Have the security system turn off lights, close drapes and

setback the temperature when we leave and turn on the alarm system. The

possibilities are only limited by our imagination!

How is the system controlled in this project?

This circuit enables one to utilize a telephone for remote switching on and off of

any electrically operated device. It does not require any physical connection to

the telephone lines or lifting of the handset. The circuit is only acoustically

coupled to the telephone instrument. Consequently, . The switching operation is

performed by making use of coded telephone ring signal.

While designing it has been ensured that the circuit is free from any false

triggering by normal telephone ring signals. Since the instrument has no

hardwired connection to the telephone line it does not affect the normal operation

of the telephone set. To avoid false triggering, suitable reset feature is

incorporated in this circuit.

Why not any other device?


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In this age of automation many other devices like microprocessor or micro-

controller, infrared remote, voice controlled devices etc. are used for the

automation purposes, but they have certain limitations which are described below

1. The use of microprocessor or micro-controller involves complexities like

microprocessor operating voltages; interrupt servicing, poling, memory

access mechanism and extensive soldering. Moreover, if we use micro-

controller or a microprocessor we cant change the working as and when

desired. The problem being, while using them we have to hardwire the code

into ROM chips and in case we need to amend we have to burn a new ROM

chip to replace the earlier one. The earlier ROM becomes useless and has to

be scraped. And this has to be done on every single time we need add

something new.

2. An infrared remote control can work for a device up to a specified range of

distance after that it cannot be used for controlling the device.

3. A voice controlled device works on a single voice and cannot be used by any

other person and have a certain range of working.


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This unit talks about how the different units of the project working. How Relays and

Transistors can be interfaced to your telephone and can be used to turn ON and OFF

your home appliances such as bulbs, tube lights, lamps or heavy-duty motors.

This project is a teleremote circuit that enables

switching ON and OFF of appliances throughtelephone lines. It can be used to switch appliances from

any distance, overcoming the limited range of infrared

and radio remote controls. The circuit described in the

project can be used to switch up to ten appliances

(corresponding to the digits 0 to 9 of the telephone

keypad). This circuit is based on the DTMF controller

circuit. DTMF means dual tone multiple frequency. The

DTMF signals on telephone instrument are used as

control signals.

When we press the star button in the telephone the pulse dialing is

converted in to tone dialing. We use this tone dialing in our project. Telephone

lines are connected to the DTMF decoder circuit including a DTMF decoder IC

8870, which is a 24 pin IC. This DTMF decoder converts the DTMF pulse into a

BCD signal. It means when we press the digit no.1 then output from decoder is0001. Circuit automatically sense and convert the DTMF signal into BCD signal.

Output from IC 8870 is connected to the next stage, which is a BCD to

Decimal converter circuit. For this purpose we use BCD to Decimal converter IC

74154. This IC converts the BCD signal into Decimal signal. It means when press

PROJECT WORKING


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the digit 2 in the keypad then 2 number output of the decimal decoder is active in

this stage.

The output of the BCD to Decimal decoder circuit is active low; therefore,

we convert this low signal into high signal with the help of inverter circuit. In this

project we have used hex inverter circuit, which is IC 4049. Hex inverter circuit

converts at a time six input signal. Since we have ten outputs in this circuit,

therefore, we have used two hex inverter ICs. Output of the inverter is high now.

Output of the IC 4049 is in the form of pulse signal, now to convert the

pulse signal into toggle signal we have used a flip-flop. The flip-flop used in the

circuit is IC 4013. This IC is a dual flip-flop IC since it has two inputs and two

outputs. These flip-flops are of D-type, i.e., the input data appears at the output

at the end of the clock pulse. This means that when the output of the previous

stage is low, the output of the flip-flop is low and when the output of the previousstage is high then the output of the flip-fop is high. If we use ten outputs of the

4049 and want all the outputs connected to flip-flop then we have to use

minimum five flip-flop ICs in the project

Output of the flip-flop is connected to the base of NPN transistor through

1k ohm resistor. Emitter of every transistor is connected to the negative voltage

and collector is connected to the relay coil. Relay is electromagnetic switch.

Relay operation voltage is 9V DC. The rectifier circuit before regulator 7805

provides this 9 V DC. Relay further ON/OFF any electrical appliance connected

to it.


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Now when we press the number 1 of the telephone keypad then one

number dyle is ON and the corresponding relay is switched ON and the electrical

circuit is completed. Now again when we press the no.1 then flip-flop output is

shifted to zero and the relay is OFF and so the electrical appliance connected to

it.

When the circuit is used to switch the relays from the telephone instrument

to which it is connected physically, the mode of operation of the telephone line

can be changed by using the star button. But when switching is done from some

other telephone instrument the working of the circuit is a little different. In that

case a coupler circuit assists the working of the project. This coupler circuit

consists of an optocoupler IC 417, a timer IC 555 and a decade counter IC 4017.

When a call is established and telephone starts ringing the optocoupler IC

detects the ring. This IC is connected to the 555 timer IC and for every ring it

makes timer IC to generate a pulse. The timer IC is connected to the decade

counter and with every pulse generated by the timer IC, the decade counter

makes one of its outputs high. A relay is connected to one of the output of thecounter IC, that connects the coupler circuit with the DTMF decoder circuit,

whenever, that output is high. That means the circuit counts a preset value of

rings and then it connects the telephone line to the DTMF decoder circuit to

perform switching action.


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