MMIINNII PPRROOJJEECCTT RREEPPOORRTT oonn

CCOORRDDLLEESSSS PPOOWWEERR CCOONNTTRROOLLLLEERR Submitted in partial fulfillment of the requirements for the award of the degree of

BACHELOR OF TECHNOLOGY

in

ELECTRONICS ENGINEERING of the

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

PRIYA T

RATHEESH CHANDRAN V R SURAJITH K

SAJI K AHMED

Under the guidance of Mr. C V ANIL KUMAR

Lecturer in electronics, college of engg. , Chengannur

DEPARTMENT OF ELECTRONICS ENGINEERING,

COLLEGE OF ENGINEERING,

CHENGANNUR-689121. August 2000

2

Acknowledgements.

Sincere thanks to all those people who have helped us in

carrying out this project successfully.

Mr. Jyothiraj V P, head of department, Electronics

Engineering, for the help extended by providing all necessary

facilities.

Our guide Mr. C V Anil Kumar for his valuable guidance

and words of encouragement given through the course of the project.

Mr. Ayoob Khan T E, lecturer in Electronics for having

coordinated our miniproject.

Special thanks to Mr. Hari V S and Mr. Nishanth Rajan

lecturers in Electronics, spending their precious time for us and

giving us their valuable ideas and suggestions whenever we needed

help.

Special thanks to Miss. Priyarenjini and Miss. Lagghima

for the help given to us.

Last but not least sincere gratitude to the almighty having

seen us through this project.

Sd/-

3

Abstract

This project Cordless Power Controller (CPC) is essentially a

remote control implemented with the help of a cordless telephone. It

has been developed as a standalone device as per the conventional DOT

standards. Connecting CPC to the telephone line makes it possible to

control lights, fans and other appliances of our home using our cordless

phone.

The interesting feature of CPC is its ability to control two

types of devices; they are ON/OFF control and ON/OFF with

speed/intensity control.

CPC is developed as a microcontroller 8051 based device.

Which controls the devices depending on the codes entered through

telephone keypad. Intensity or speed variation is obtained by altering

the phase of the gate pulses given to the triac for triggering it

4

Contents

1. INTRODUCTION 1.1. Cordless Power Controller

2. REVIEW

a. Telephone signaling systems

b. DTMF description

c. Interface to the telephone line

d. The TRIAC

3. EXPERIMENTAL PROCEDURE

a. Hardware details

b. Software details

4. CONCLUSION

5. APPENDIX

5

Introduction

6

11.. CCOORRDDLLEESSSS PPOOWWEERR CCOONNTTRROOLLLLEERR

We live in a world of automation and full of facilities only because of technology. In this world we have become so much addicted to technology so

that we would rarely try to turn on a television ourselves rather than searching

for the missing remote control for turning on the television.

Controlling electronic devices and domestic appliances using a remote

control is an attractive facility provided in the present consumer electronics

products. This product CPC (cordless power controller) is essentially a remote control implemented with the help of a cordless phone. This makes it possible to

control lights, fans and other appliances of our home using our cordless phone.

This in fact eliminates the need of another remote controller in our home.

The CPC is connected between the receiver and the telephone lines so

that the signals at the input port of CPC will be same as from ordinary telephone

that will be in accordance with the conventional DOT standards.

The working of the CPC can be summarized as below

1. On reset, CPC would be in the telephone mode. Power control mode

(PCM) only after dialing a particular code. (For eg.33#). After the code

has been entered, CPC switches to the power control mode. The

indicator and the tone generator tell us that the device has been

selected. And the relay disconnects telephone from the lines.

2. In the PCM, we can select different devices by dialing appropriate

codes for each (For eg.1 for bulb,2 for fan ) etc.

3. After selecting a device we can control the ON/OFF state of the device

by entering a different key (For eg. 3).

4. If the device selected is fan, we can con troll the speed of it by using

two dedicated switches, for increasing and decreasing the speed

respectively.

5. The mode changes automatically to telephone when the phone is

disconnected. Thus the device works in two modes namely

7

1. Power control mode

2. Telephone mode

The firing pulses for the TRIAC are generated by the -controller. The phase of the firing pulse can be varied and hence the firing angle of the TRIAC.

By varying the firing angle we can control the brightness of the lamp, speed of

the fan etc. Isolation can be given by using the pulse transformer, at the

triggering side. The entire software for -controller is stored in an EPROM. The product will be very useful for bedridden patients, handicapped

individuals and even lazy people!!!

8

Review

9

2. TELEPHONE SIGNALLING SYSTEMS

2.1 .1. Touch Tone

Touch-tone dialing is a method of sending signals from telephone

customer's premises to central offices and beyond. Compared to rotary dialing

its principal advantages are:-

1. All the signaling energy is in the voice frequency band, making it

possible to transmit signaling information to any point in the

telephone network to which voice can be transmitted

2. Touch-tone dialing is faster, reducing the dialing time for users and

reducing he holding time for central office for common equipment.

3. It provides a mean for transmitting more than ten distinct signals.

4. It provides a more convenient signaling method.

The development work that led to the introduction of touch-tone dialing

began at Bell Laboratories in the mid 1950's. The dialing unit had mechanical

linkages that plucked two out of six metal reeds, each of which was resonant at a

specified frequency. When a customer pushed any of thee ten buttons, two reeds

were plucked to form a signal coded to corresponding digit. The energy so

generated was transferred inductively to coils in the station set network and so

transmitted to receiver at central office. Although this mechanism was

cumbersome, the performance of the equipment and the reaction of the

customers pointed the way to an ultimately feasible system and indicated a

favorable public response to push-button signaling.

Using this new technology a compact multi-frequency oscillator

equipped with push buttons for selecting and controlling voice frequency signals

10

was developed in the late 1950's. The oscillator was particularly adapted to the

low and variable power available from the central office battery over the range

of the existing loops to the station set. The oscillator design the central office in

the presence of the noise from numerous sources that is always present on the

telephone circuits, but not so high as to exceed crosstalk. The concept of a four-

by-four frequency code resulted in a relatively simple mechanical system at the

station set.

Concurrently with these electrical and mechanical developments, human

developments and performance ratings of button arrangements were made. The

optimum size, spacing, travel and operating force of the buttons were

determined. It was also established that feedback of signal tones through the

telephone receiver was desirable.

The purpose of technical details was to test the operational capabilities of

the system and its components. These include:

1. The dialing and supervisory capabilities of the system over typical and

limiting plant conditions. A sample of adequate size and diversity including

various gauges of loaded and non-loaded cable and wire and exposure to

various environmental conditions was needed.

2. The effectiveness of the protection provided in the system against false

signals. It was anticipated that signal like impulses would be generated by

speech, line noise, test supervisory tones that exist on telephone circuits.

3. The reliability, stability and maintenance requirements of the equipment and

its components under typical conditions.

4. Customer usage characteristics such ass dialing speed, learning rate, signal

pulse duration, error types and rates.

5. The results of the second set of trials led to the conclusion that a practical

new dialing scheme could be developed based on the technical concept of

the system and components used in the technical trials.

11

2.1.2. Touch Tone Dialing Scheme

In the previous section various advantages of touch tone dialing was

listed. Initially the only objective was to reduce the dialing time. The

development was governed by two factors. The rotary dial had been around for

several decades and was very inexpensive. The power dissipation, variation of

gain among devices, reliability and cost were all issues. One scheme that was

developed involved the generation of damped waves by interrupting the direct

current through the coil of an inductor capacitor tuned circuit. Very soon it

became clear that it was essential to be able to transmit customer's signals end to

end. Two requirements from the end to end signaling objective:

1. The signals must not contain an out of band component such as DC step.

2. Sustained rather than damped signals must be used to maintain adequate

signal to noise margins for the wider range of transmission losses when

two-customer loops are involved.

The first of these two requirements the need for the signals to be wholly

contained within the voice frequency band also brings with it the

problem of vulnerability to talk off. The second reintroduced the

uncharted domain of active devices.

2.1.3. Choice of Code When only voice frequencies are employed, protection against talk off must rely on statistical tools. This protection is required only during inter digital

intervals; speech interference with valid signals can be avoided by the

transmitter disablement when a push-button is operated. Since signals with a

simple structure are prone to frequent limitation by speech and music some form

of multi-frequency code particularly difficult of imitation is indicated. If the

signal frequencies are restricted to binary fashion, the greatest economy in space

12

of frequency results from the use of all combinations of N frequencies, yielding

n=2 exp. N different signals.

To minimize the number of circuit elements, as well as to reduce the

sharing of amplitude range P should be as small as possible, yet be larger than

unity for the sake of talk off protection. Let us thus examine codes in which

P=2. If one can be found that is not readily imitated by speech or music there is

no merit in choosing P higher than 2.

There are further advantages, as we shall see in imposing the further

restriction that, with P=2, the frequencies for each combination fall respectively

into two mutually exclusive frequency bands. If for example 15 or more

combinations are required N must be at least 8. In the 4 by 4 code, eight signal

frequencies are divided into two groups: group A, the lower group of four

frequencies and group B, the higher group of the four frequencies, resulting in

16 combinations.

2.1.4. Band Separation and Limiter Action With a two group arrangement it is possible at the receiver to separate the two frequencies of a valid signal by band filtering before attempting to

determine the two components of a signal renders reliable discrimination

between valid signals and speech or noise simpler for two reasons:

1. Each component can be amplitude regulated separately.

2. An instantaneous extreme limiting can be applied to each component

after band separation.

It is the characteristic of extreme instantaneous limiters that they

accentuate differences in levels between the components of an incoming multi-

13

frequency signal. This property is used with FM radios and is referred to as

limiter capture. This may be used to provide guard action to reduce the

probability of false response to speech.

Guard action of the type that has been discussed requires that only one of

the two tones making up a valid signal be admitted to each limiter. To derive the

fill benefit of limiter guard action, as much of the speech spectrum as possible

should be given access to the limiter. A band pass filter preceding the limiter to

separate two components of a valid signal, would defeat this objective, since it

would permit competition for limiter capture between a signal frequency and

only portion of the speech burst lying in the same band. However a filter

attenuating merely the other group of frequencies allows competition with the

whole speech spectrum except with the attenuated band.

2.1.5. Choice of Frequencies

Attenuation and delay distortion characteristics of typical combinations

of transmission circuits were such that it is desirable to keep the frequencies of a

telephone signaling system within the 700-1700 Hz range.

The choice of frequency spacing depends in part on the accuracy of the

signal frequencies. It was expected that signals generated at the station set could

be held within 1.5 % of their nominal frequency values and that the pass bands

of the receiver selective circuits could be maintained within 0.5 % of their

nominal ranges. On the basis of these numbers the selective circuits of the

central office receivers need to have recognition bands of at least 2 % about the

nominal frequencies.

The standardization of the amplitude at the output of the limiters permits

an accurate definition of the recognition bands in the receiver, independently of

14

levels at the receiver input. As a result frequencies may be spaced closely,

approaching the recognition bandwidth of 4 %.

Another factor can profitably be taken into account in the selection of a

frequency spacing. To reduce the probability of talk off the combination of

frequencies representing bonafide signals should be such that they are not

readily imitated by the output from the speech transmitter. In a receiver with

guard action no sound composed of a multiplicity of frequencies at comparable

levels is likely to produce talk off.

GROUP A GROUP B

(Hz) (Hz)

697 1209

770 1336

852 1477

941 1633

A family of frequencies that avoids a large proportions of troublesome

combinations and also meets all other requirements. The adjacent frequencies in

each group are in the fixed ratio of 21:19.

All frequencies are essentially within the 700-1700 Hz range, and the

spacing is adequate to accommodate the recognition bands. The 16 pairs of

frequencies representing valid signals avoid low order ratios.

15

2.1.6. Choice of Amplitude

Since signaling information does not bear the redundancy of spoken

words and sentences yet must be transmitted with a high degree of reliability, it

is advantageous for the signal power to be as large as permitted by the

environment. For subscriber loops the maximum slope between 697 and 1633

Hz is about 4 dB. The attenuation increases with frequency. The reduction in the

maximum level difference at the receiver in the two signal components can be

achieved by transmitted the group A frequencies at a level 3 dB higher than that

of group A frequencies. In this way the nominal amplitude difference at the

receiver input between the two components of a valid signal is never more than

5 dB. At a receiver involved in end to end signaling the minimum power was

estimated to be 32.5 dB.

2.2. DTMF DESCRIPTION

To speed up the dialing procedure and to make it more reliable, the DTMF dialing system is used. In this system, digits are transmitted as two tones

simultaneously. This explains the name "Dual Tone Multi Frequency". It is also

known as DTMF dialing or mf dialing. The tone frequencies are selected to

avoid harmonic interference from speech signals. There are eight frequencies

defined in the DTMF system: four in a low frequency group (679-941 Hz) and

four in a high frequency group (1209-1633Hz).

A valid digit is defined as one of the low frequency group together with

one tone out of the high frequency group. In total, there are sixteen

combinations possible but we use only the digits 0-9. The maximum dialing

speed with a DTMF system is typically 7 digits per second, i.e., a tone burst of

16

70 msec. With the pulse dialing system, the speed varies between 1.1 to 0.56

digits per second. The DTMF is therefore ten times faster. The major application

for DTMF is low speed data transfer.

2.2.1 Generation of DTMF

1209 Hz 1336 Hz 1477 Hz 1633 Hz 697 Hz 1 2 3 A 770 Hz 4 5 6 B 852 Hz 7 8 9 C 941 Hz * 0 # D

Two tunable oscillators, one for the low frequency group and one for the high frequency group can be used to generate DTMF tones as shown in the

figure above.

However, due to accurate frequency demand, ICs were put together with

a crystal oscillator and two synthesizers which generate the DTMF tone

digitally. Although, it cannot synthesize the exact DTMF frequency, an

inexpensive crystal has turned out to be the most popular type of DTMF

synthesizer clock that generates a frequency of 3579545Hz and can be divided

down to the DTMF frequencies with only a small error.

17

2.2.2. Tone Details The exchange will use standard DTMF frequencies for the calling

number on the line. The duration of the digit shall be 50 msec each.

2.3. INTERFACE TO THE TELEPHONE LINE

The DTMF tones generated by the DTMF dialer must applied to the

telephone line respecting the AAC and DC requirements of the PTT. Most

bipolar DTMF dialers incorporate an on chip line interface. This approach

results in very simple and efficient circuit designs. The DTMF dialer is powered

from the speech circuit peripheral supply point. The DTMF tones are transmitted

to the telephone line via the speech circuit line interface. The mute signal

generated by the DTMF dialer, controls the speech circuit and determines when

to transmit speech and DTMF signals. The switch over from speech mode to

dialing mode can be realized without noticeable audible clicks.

If the speech circuit passes part of the signals on its DTMF input to the

earpiece output, a confidence tone will be introduced. This approach is called

the common line interface architecture because both the speech and dialing parts

of telephone are connected to the by the same interface.

If an appropriate speech circuit is not available for interfacing the CMOS

DTMF dialer to the telephone line, a separate line interface for the dialer must

be used. This requires a large number of discrete components.

2.4. THE TRIAC The Triac is a three terminal, gated npnp device for controlling ac

current in either direction. Originally designated as a bi-directional triode

thyristor, it is more commonly referred to as Triode ac semiconductor (TRIAC).

18

Either positive or negative gate signals may be used to trigger the triac

into conduction. This characteristic helps to simplify circuit design. The load or

main current terminals are designated as MT1 and MT2. Usually, MT1 is taken

as the point of reference for voltage and current measurements made and the

gate terminal. Maximum current and offset voltage ratings are of the order of 40

A and 800 V, respectively.

2.4.1.1. Theory of Operation

The n and p semiconductor sections between MT1 and MT2 can be

considered as parallel npnp and pnpn switches. The triac is similar to connecting

two SCRs in parallel for bi-directional, or full wave, current conduction. The

primary difference between parallel SCRs and the equivalent switching sections

of the triac lies in the gate structure and trigger methods.

The triac can be switched to conduction either by gate triggering or by

two other operating conditions- exceeding the break over voltage rating, or a

sharp rise in off-state voltage. These methods of conduction are not employed in

normal triac operation but they may be considered as limiting factors in circuit

design. As a result, triacs switched to conduction by either of these mechanisms

will not be damaged, since the triac merely switches to the on-state condition. In

general, the triac requires no external over voltage protection.

2.4.1.2. Voltage Break over Turn-On

The triac can be switched into conduction in either the first or third

quadrant by excessive voltage across the MT2- MT1 terminals. Triac control

circuits are designed so that the rated the rated minimum blocking voltage

(VDRM) is never exceeded. Transients on the ac power line can cause the off-

19

state voltage to rise above voltage break over point. When this happens, leakage

current through the reverse biased junction avalanches, and the triac is latched

into conduction.

2.4.1.3. Static dV/dt Turn-On

A triac can be switched into conduction by a sharp increase of the off-

state voltage. The symbol dV/dt stands for the rate of change of voltage with

respect to time. The peak off-state voltage does not have to exceed the voltage

break over point for this mode of switching to occur. Generally referred to as the

critical or static dV/dt, the rapid increase in voltage across the triac results in a

charging current through the internal capacitance of the device. When this

charging current equals or exceeds the gate trigger current (Igt), the triac is

triggered into conduction. The resulting current in a capacitor is a function of the

capacitance and the rate of change of voltage across the capacitor. This is given

by the equation:

I=C * dV/dt

Where,

I is the charging current in amperes,

C is the capacitance in farads,

dV is the change in volts,

dt is the time (in seconds) associated with the voltage change.

Typical static dV/dt ratings for triacs range from about 10 V/secs for low power devices to about 100V/microsecs for high power devices.

A snubber network, consisting of a series resistor and capacitor connected

across the MT1 and MT2 terminals, can be used to protect a triac from sharp

increases in the off-state voltage. The charging capacitor momentarily places the

voltage across the resistor and the energy contained in the sharply rising portion

of the voltage waveform is dissipated in the resistor. Snubber circuit can also

20

protect the triac against voltage transients, which exceed the break over voltage

level. The design of snubber circuits must take into account peak line voltages,

load characteristics, and time constant of the RC network must be small when

compared to the ac load conduction time.

2.4.1.4. Triac Switching Time and Commutation Considerations

Most triacs possess a gate control turn on time (tg) of the order of 1.5 to 5

microseconds. The triac should be triggered with a fast-rising current waveform

for reliable turn on characteristics. Care should be taken to avoid exceeding the

gate power dissipation limits of the device being used. Unlike the SCR, the triac

is turned on twice each ac cycle. Thus the triac must be turned off promptly at the

end of each cycle so that it can be turned on in the opposite direction for the next

half cycle. The successive turn on and turn off is referred to as commutation.

The switching involved with a 60-Hz source may result in a commutation

time of 1ms or less. During this short interval, load current must drop below the

holding current (IH) of the triac to permit full turn off of current. Further more

the triac must be gated into conduction at the proper time during the next half

cycle. With resistive loads successive turn off and turn on is fairly easy to

accomplish. The current in a resistive network is in phase with the applied

voltage.

Inductive loads such as motors and transformers pose a difficult task for

triac commutation. The current in an inductive load is lagging the supplied

voltage. This lagging load current holds the triac in a state of conduction past the

end of the ac half cycle. When the load current drops below the holding current,

the triac switches to the off-state conditions. By this time the voltage associated

with the next half-cycle has risen to an appreciable level. This permits a sudden

increase in the voltage across the triac and this may prematurely trigger

conduction during the next half-cycle. The maximum rate of rise of an off-state

21

voltage that will not trigger the triac into conduction is known as the

commutating dV/dt rating. This is usually expressed in volts per microsecond.

More critical than static dV/dt limitations, the commutating dV/dt ratings for

triacs range from 1 to 5V/microsec. Snubber circuit can be used to eliminate this

problem.

2.4.1.5. Operating Temperature Characteristics

As with other thyristors, the operating characteristics of the triac may vary

considerably with changing temperature. All temperature related specifications

are usually referenced to case temperature. Gate trigger current and gate trigger

voltage both vary inversely with case temperature-higher temperature requires

lower amplitude gate signals. The minimum dc holding current also varies

inversely with case temperature. Dc holding current is also related to the voltage

polarity across the main terminals. i.e.; dc holding current for first quadrant may

exceed thee third quadrant dc holding current by 10 to 40 percent.

The design of triac control circuits requires that careful attention be given

to temperature characteristics concerning such operating parameters as gate

rigger signals, dc holding currents, and commutating conditions. In particular,

low temperature operating environments require higher amplitude trigger signals

for reliable operation.

2.4.1.6.Triac Specifications

Like SCRs, triacs are available in a wide range of current handling

capabilities and types of packages. The MAC3030-40/MAC3030-401

specification contains an interface circuit for use in digital control circuits.

22

2.4.2. TRIAC TURN_ON METHODS

Triacs may be triggered into conduction by a variety if methods. The

particular application will generally dictate the method if triggering to be

employed. The gate circuits can be designed for static, zero voltage, or phase

switching techniques. Each method offers specific advantages and disadvantages.

2.4.2.1 Static Switching

Triacs employed in static switching circuits offer many advantages over

mechanical switching using relays or manually operated switches. This electronic

switching eliminates arcing and contact boune, both of which are problems with

moving physical contacts. These factors result in more reliable operation and

virtual elimination of rfi.

A resistor is connected to the gate circuit to limit the gate current and is

about 100 ohms.

2.4.2.2. Zero-Voltage Switching During zero voltage switching, the triac conducts for virtually 360 of

each cycle, and full power is delivered to the load. The triac is triggered at

approximately the 0 and 180 degree points in the ac cycle. During power off

periods, the triac is held in a non-conducting state. The ratio of power-on to

power-off intervals determines the average power applied to the load. The power-

control time base may consist of intervals of 30 ac cycles (one half second).

If the triac is switched on for 15 full cycles during each one- half-second

interval, the average power being applied to the load is one-half of full power.

Triac zero crossing switching circuits are used in industrial control and

related applications. Like static switching, zero crossing power switching systems

23

are virtually free of radio frequency interference problems. Another important

advantage is the inherent differential control capability that exists when gradual

changes in average power can be applied to a load.

2.4.2.3. Phase Control Switching

Triac phase-controlled gate circuits allow conduction of load current

during a specified portion of each ac half cycle. Simple resistive gate switching

circuits can be employed to trigger the triac for firing angles up to 90 degree in

each half cycle. Resistance-capacitance phase shifting networks are used to delay

the firing angle up to nearly 180-degree.

The performance of phase controlled gate trigger circuits can be greatly

improved by the use of a trigger device. For low voltage levels, the trigger device

exhibits high impedance. Except for a small leakage current, no gate signal is

presented to the triac during this time. When the applied voltage is increased to

the break over level, the trigger device suddenly latches into conduction. This

presents a fast rising trigger signal to the triac, resulting in reliable turn on of load

current.

The diac is one of the more common trigger devices in use today. Other

trigger devices used in triac gate circuits include unijunction transistors (UJTs)

and special two-transistor configurations usually fabricated as one integrated

circuit.

24

Experimental procedure

25

3.1. HARDWARE DETAILS

This section deals with the technical aspects of this project. As

shown in the block schematic, the project consists of several ICs as mentioned

earlier and other hardware circuits. We will discuss about each of the

components and their functions.

The entire project can be divided in to three blocks

1. MCU card 2. Input card 3. Output card 4. Power supply unit

3.1.1. MCU card

MCU card contains the micro controller, EPROM address latch etc. It has

seven input lines from the input card. They are connected to port3 and are

namely,

P3.1 Hook detector P3.2 DTMF interrupt P3.3 ZCD interrupt P3.4 BCD P3.5 BCD P3.6 BCD P3.7 BCD MCU card has 3 output lines (port1) and can be listed below.

P1.0 mode selector P1.1 lamp P1.2 firing pulses

Output p1.0 goes to a Darlington pair, which drives a relay. This relay

switches the device between two operating modes, Telephone mode and Power

26

control mode. An LED indicator is also attached with this relay. P1.1 also goes

to a Darlington pair, which controls the lamp (ON/OFF). The firing pulses for the

TRIAC are output through P1.1.These pulses directly go to the optocoupler

MOC3011 through buffer. All the output lines are connected through the buffer

IC74144 in order to prevent the loading of port1.

3.1.2. Input card

The input card consists of the following handshake signals, which

altogether produces seven inputs to the MCU. The seven inputs have already

been discussed above.

3.1.2.1. DTMF Decoder -HT 9170

The HT 9170 is a Dual Tone Multi Frequency (DTMF) receivers

integrated with digital decoder and band split filter functions. Digital counting

techniques are used in the decoder to detect and decode all the 16 DTMF tone

pairs into a4-bit code output.

While the accuracy switched capacitor filter are employed to

divide tone (DTMF) signals into high and low group signals. A built-in dial tone

rejection circuit is provided to eliminate the need for pre- filtering.

3.1.2.2. Functional Description

The HT 9170 is tone decoder. They consist of three band pass

filters and two digital decoder circuits to convert tone (DTMF) signal input

digital code output. An operational amplifier is built in to adjust the input signal

for users. The pre filter is a band rejection filter that reduces the dialing tone that

is from 350 Hz to 400 Hz. The low group filter filters low group frequency

signal output whereas the high group filter filters high group frequency signal

27

output. A zero crossing detector with hysterisis follows each filter output. When

each signal amplitude at the output exceeds the specified level it is transferred to

full swing logic signal. When input signals are recognized to be effective, DV

becomes high, and the correct code of the tone (DTMF) digit is transferred.

3.1.2.3. Hook Detection Circuit

The hook detection circuit is a special type of circuitry, which is

used to check whether a particular telephone set, is on-hook or off-hook. The

output of this circuit is fed to the 8051 MCU port, which checks the status of the

telephone.

The circuit is connected to the telephone line along with the

telephone set, in parallel .The telephone line offers a line voltage of 48V.This

line carries the DTMF tones corresponding to the calling party number as

transmitted by the exchange. As mentioned earlier, the telephone goes on-hook

and off-hook very frequently .At on-hook condition, the output from this

detection circuit is zero. Once the telephone goes off-hook, the output across

both the transistors (BC 546) goes to logic high of 5V.

3.1.2.4. ZCD-zero crossing detector

The ZCD provides the reference signal for the MCU for generating

pulses. The delay between the firing pulses and ZCD signals is varied to control

the firing angle of TRIAC. The ZCD provides narrow pulses having a width of

about 150 sec, at the start of the each +.

The input ac is clipped using two antiparallel diodes. This clipped signal

is fed to the 339 components (The 339 IC is a Quad comparator)

28

3.1.2.5. 339 comparator

The 339 Ic is a Quad comparator containing four independent voltage

comparator circuits, connected to external pins. Each comparator has inverting

and non-inverting inputs and a single output. The supply voltage applied to a

pair of pins powers all four comparators. Even if one wishes to use one

comparator only, all four will be drawing power.

The output of the comparator would be a square wave with period 20m

sec. we uses a pulse of width 100 sec at every 10m sec interval in order to interrupt the microcontroller (int1). In order to generate these pulses, the square

wave is fed to IC 74123. It is a dual retriggerable monoshot. One of the

monoshots is made positive edge triggered, ie sensitive to the clock and the

other is made sensitive to the negative edge of the clock.

The value of resistors and capacitors of both of the monoshots are

designed to achieve the desired pulse width of 100 sec. Finally the outputs of both monoshots are ORed to get the desired ZCD signal.

3.1.3. Output card

This board consists of two Darlington pairs, triac and driver circuits and

a buffer. One Darlington pairs are used to drive the relays that control the lamp

and the other for switching between the two modes of CPC. Triac circuit is used to

control the power varying loads like fan.

29

3.2. SOFTWARE DETAILS

The project is totally based on the control by -controller hence the programming has been carried out in assembly language and downloaded on to

the program memory. The entire program is explained by the flowcharts as

shown

30

No Yes No Yes

Start

Is hook Off? ie P3.1=1?

Enables int0, Sets hook bit

Is hook On? ie P3.1=0?

Disables int0, Resets mode to telephone mode.

Initialization of SP Ports, timer, Mode, Interrupts, hook&

fan bits

31

Yes Yes No Yes No Yes No

Key press

DPTR loaded From memory with Address of LT2

Is Modebit Set?

B

Is A =

@DPTR ?

Decrements R7 (Contains the no: of digits in code)

Is R7=0?

Memory loaded with starting address of LT2 disables int0

Set Mode bit

C D

A

Disables all interrupts, read

port3

32

DPTR incremented and stored in memory

B

E F

Mode changed to PCM

Enable all interrupts

Ret I

33

Yes No Yes No . Yes Yes No No No Yes

A

Is A=light Select?

Is A= fan Select?

Is A= Device Toggle?

Device bulb is selected

Device fan is selected

Is Device

bulb? Complements bulb state

Complements Fan bit

Is Device

fan?

E F

34

Yes Yes No No Yes Yes No No

E F

Is A=( - )

Is A=( + )

Is Delay step>0?

Decrement Delay step

Is Delay step

35

ZCD

Disable all int Except int0

Gets the actual delay Count from memory And loads counter.

Enables counter Counting and Counter0 interrupt

Ret I

36

No Yes

Counter0

Counting reset, counter int disabled count loaded in R3

Complements port for fan

Dec r3, Is r3=0?

Ret I

Call delay for width of the pulses

37

Delay

Dec r2, Is r2=0?

Return

Load count for 5m sec in R2

38

Conclusion

39

The CORDLESS POWER CONTROLLER (CPC) by us as

explained throughout is a standalone device that can be interfaced to

a cordless telephone. The main function of this device as mentioned

is to control home appliances like lamp, fan etc using a cordless

phone. Our design is restricted to the control of loads rated at 110V

AC. The power handling capacity can be improved by using the

optocoupler MOC 3062 instead of MOC 3011. The number of

devices controlled here is two. This can be increased by using the

unused port bits. The functions like caller identification and number

directory and dialing systems can be easily integrated with this. The

tele-remote facility can also be added to this project by making slight

changes in the hardware and software.

40

Appendix

41

Bibliography

42

References:

1. The 8051 Microcontroller Architecture, Kenneth J. Ayala Programming & applications

2. Thyristor Theory and Application Clay Laster Sites visited:

1. http://www.acebus.com 2. http://www.motorola.com

3. http://atmel.com

4. http://icmaster.com

Under the guidance ofCHENGANNUR-689121.

August 2000Acknowledgements.ContentsIntroductionReview

2. TELEPHONE SIGNALLING SYSTEMS2.4. THE TRIAC

3.1. HARDWARE DETAILS3.1.1. MCU card3.1.2. Input card3.1.2.1. DTMF Decoder -HT 91703.1.2.3. Hook Detection Circuit

3.1.3. Output card3.2. SOFTWARE DETAILS

AppendixBibliography