Long Range FM Transmitter 1

Long Range FM Transmitter 1

Long Range FM Transmitter 1

How to make a long range FM transmitter at low cost

Description

The use of transmitters which have a more powerful output than the ‘flea-power’ are sometimes required when there are many obstacles in the path of the surveillance transmitter and monitoring station receiver, or the distance between them is too far so as to make a low powered device feasible. Whereas a typical microtransmitter will produce an RF power in the order of just a few milliwatts, i.e. a few thousandths of a watt, the VHF-FM transmitter described has a power output of between around a half and 2 watts, depending on the power source, which may be anywhere between 6 volts and 30 volts d.c. The battery or batteries should be of the alkaline high power type, since the current drain will be found to be relatively higher when compared to microtransmitter current drain. The power output of this device is somewhat proportional to the current drain and so therefore both may be decreased by altering the value of R6 to a higher resistance, or a variable resistor with a value of around 1k may be introduced in series with the existing R6, so as to give a variable power output. The variable resistor must not be a wirewound device because this would act as an inductor which will cause feedback problems.The audio input to the power oscillator, which incidentally is formed by TR2 and associated components, is derived from a piezoelectric microphone which drives the simple audio frequency amplifier TR1. The input of the audio amplifier is controlled by the gain pot R1, which selects the correct amount of voltage that is generated by the piezoelectric microphone, then connects this signal to the base of audio amplifier TR1 via C7. It may be found that there is insufficient housing space for a bulky piezoelectric microphone, so with a slight modification to the circuit, it is possible to employ an electret microphone insert as shown. Since the RF field that is generated by this transmitter is relatively large, the problem of RF feedback may very well be encountered. This may be overcome by placing the transmitter inside a metal enclosure, keeping all internal wiring as short as possible and the aerial wire.

Component listing for 1 watt transmitter

Resistors Semiconductors R1 = 27k TR1 = BC547 R2 = 330k TR2 = 2N2219 fitted with heatsink R3 = 5k6 MIC = piezoelectric microphone R4, 5 = 10k R6 = 100R

L = 6 turns 22 gauge enamelled wire wound on 3⁄16″ former

Capacitors

C1, 2, 3, 8 = 330 pF C4 = 2–10 pF trimmer C5 = 4p7 C6 = 1 nF

C7,C8 = 40uF/25V Electrolytic

Circuit diagram for Long range FM Transmitter

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Remote toggle switch circuit

Remote toggle switch circuit

Remote toggle switch circuit

Description.

In application level this circuit is similar to that of the circuit given previously. The only difference is in the approach. This circuit is designed by using another method. Using this circuit you can toggle any electrical appliance between ON and OFF states by using your TV remote. The only requirement is that your TV remote should be operating in the 38 KHz.

 

The IC1 (TSOP 1738) is used to receive the infrared signals from the remote. When no IR signal from remote is falling on IC1, its output will be high. When the IR signal from the remote falls on the IC1, its output goes low. This triggers the IC2 which is wired as a monostable multivibrator.The output of the IC2 (pin6) goes high for a time of 1S (set by the values of R2 and C3.This triggers the flip flop (IC2) and its Q output (pin 15) goes high. This switches on the transistor, which activates the relay and the appliance connected via relay is switched ON. For the next press of remote the IC1 will be again triggered which in turn makes the IC2 to toggle its output to low state. The load will be switched OFF. This cycle continues for each press of the remote. The pin 6 and pin 4 of IC1 are shorted to avoid false triggering.The diode D1 can be used as a freewheeling  diode.

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a good quality PCB or common board.
• The circuit can be powered from  a 5V DC regulated power supply.
• The capacitors must be rated 15 V.
• The IC1&IC2 must be mounted on holders.
• The current capacity  of relay determines the load circuit can switch.Use a high amperage(`10A or above) relay for driving large loads like motor,heater etc.

 

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Remote controlled appliance switch circuit

Remote controlled appliance switch circuit

 

Description.

Here is a versatile remote controlled appliance switch that can ON or OFF any appliance connected to it using a TV remote.

 

IR remote sensor IC TSOP 1738 is used for recieving the signal. Normally when no signal is falling on IC3 the output of it will be high.This makes Q1 OFF.When a signal of 38 KHz from the TV remote falls on the IC3 its output goes low.This makes Q1 conduct and a negative pulse is obtained at pin 2 of IC 1  NE 555.Due to this IC1 wired as a monostable multivibrator produces a 4 Sec  long high signal at its out put.This high out put is the clock for IC 2 which is wired as a Flipflop and of , its two outputs pin 3 goes low and pin 2 goes high.The high output at pin 2 is amplified to drive the relay .For the next signal  the outputs of IC2 toggles state. Result, we get a relay toggling on each press on the remote.Any appliance connected to this circuit can be switched ON or OFF.

Circuit Diagram with Parts List .

Notes.

• Before wiring the circuit make sure that the carrier frequency  of the TV remote you have is 38 KHz.For that wire the sensor part only ,point your remote to the TSOP1738 and press any switch.If  out put of TSOP1738  goes  low them ok, your remote is of 38Khz type.Nothing to worry almost all TV remote are of this type.
• You can use any switch because for any switch the code only changes,the carrier frequency remains same.We need this carrier frequency only.
• Assemble the circuit on a good quality PCB or common board.
• The appliance can be connected through NO or NC  and contacts of the relay .

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PC TO PC FIBER OPTIC COMMUNICATION

PC TO PC FIBER OPTIC COMMUNICATION

The above project uses two nos transreceiver modules ,and the circuit communicates at 9600 kbps. ‘c’ codes comes with along  with project

PC TO PC LASER COMMUNICATION

PC TO PC LASER COMMUNICATION

The above project uses two nos transreceiver modules ,and the circuit communicates at 9600 kbps. ‘c’ codes comes with along  with project

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PROJECT ON WIRELESS DATA AND VOICE COMMUNICATION THROUGH INFRARED-LED

SYNOPSIS of the month

TITLE OF THE SYNOPSIS:-

“Conceptual designs development & demonstrations of a
WIRELESS DATA AND VOICE COMMUNICATION THROUGH INFRARED-LED”

OBJECTIVES:-

To Design a circuit of an electronic infrared communication system.
Develop new ideas to implement this circuit purposely.
To study the circuitry and different types of components & DTMF generator, DTMF decoder, op-amp and infrared-LED in the circuit.

INTRODUCTION

For years, infrared LED has been merely a system for piping light around corners and into the inaccessible places to allow the hidden to be lighted. But now, infrared LED has evolved into a system of significantly greater importance and use. Throughout the world, it is now being used to transmit voice, television and data signals as light waves. Its advantages as compared with conventional coaxial cable or twisted wire pairs are manifold. As a result, millions of dollars are being spent to put these light wave communication systems into operation.
One of the most interesting developments in recent years in the field of telecommunication is the use of laser light to carry information over large distances. It has been proved in the past decade that light wave transmission through laser light is superior than that achieved through wires and microwave links. Typically, infrared LED has a much lower transmission loss per unit length (0.15-5db/km) and is not susceptible to electromagnetic interference. Economically also, it serves our purpose. The ever increasing cost and the lack of space available in the congested metropolitan cities asks for advent of a less costly system.
The conventional telephonic systems use copper wires, which easily get oxidized and as such require high maintenance cost. The laser light being made of glass are non-reactive and hence economical. Also, the noise pick up by the copper wire or in electrical signals is quite substantial whereas in laser light, the noise pick up is negligible.

Basic elements of a infrared LED system

Applications
(i) Applications for video transmission include high quality video Trunked from studio Transfeter, Broadcast CATV video, Video Trunking within city or between cities, Baasedand Video for closed.

BLOCKDIAGRAM

CONSTRUCTION AND WORKING

MIKE: Its converts sound signals into electrical signals.

AMPLIFIER (A): Signals from mike are amplified so that it can drive to infrared-LED.

INFRARED-LED: It carries signals.

PHOTO TRANSISTOR: The electrical signals are regained from the optical signals.

AMPLIFIER (B): Energy of signals is amplified to drive the speaker.

SPEAKER: Electrical signals which are amplified are reconverted into sound signals at the speaker.

DTMF CODER: It is generates the DTMF signal corresponding to the number entered from the keyboard.

DTMF DECODER : It is fed to DTMF decoder which gives the binary output corresponding to the signal received from the transmitter.

DECODER DRIVER : To drive the 7 segment display.

The circuit

The main part of Circuit is an amplifier.  This sound signals (even at a distance of 2 meters from the mic) are picked up by the condenser microphone and converted into electrical variation, which are amplified by the op-amp. (Operational amplifier)  IC- 741 is use in the inverting mode with a single supply using divider network of resistor the gain of IC can be set be varying the feed back through R5/6  resistance (can place a 1M variable) here the output of IC is further amplified buy the push-pull amplifier using transistor BC.548/558 pair, in this circuit are R2 is feed back resistance with R1/8 and C1/3 to connected IC-741.  The IC’s pin 2 is connect VR1 (variable resistance) through connect to O/P of T1 (transistor) also use 6volt DC. The microphone should be placed near the circuit with the shield wire to suppress tune. The output of the amplifier is taken from emitter of two transistors, with a filter C5 from speaker.  Same process continues in the second amplifier.

CIRCUIT DESCRIPTION OF SWITCH SECTION

This project was based on photo diodes and photo transistor. Photo diodes had been used as a transmitter and photo transistor as a receiver. This project had been divided in two part, First part transmitter section and second part receiver section. Slide switch selected to voice communication and data.

TRANSMISSIONSECTION :When switch key is pressed, circuit is energised. The output of The transmit IR beams modulated at same frequency 1KHz. The receiver uses infrared module. The IR- signal form the transmitter is sensed by the receiver sensor.

RECEIVER SECTION:- This section is worked as a Flip-flop (Bistable). IC-3 is decade counter, its Pin No.14 is input and Pin No. 2 output. The output of frequency detector stage is used, via a flip-flop, to switch ‘ON’ or switch ‘OFF’ a LED alternately. The receiver uses infrared modules IR-signal from the transmitter is sensed by the sensor through and its output PIN 1 goes low and switched LED. IC-3 is worked on clock pulse which receives to infrared modules at Pin No. 14. Its output at Pin No 2 throughes high.
The output of IC-2 is also used for lighting LED-1 indicating presence of signal. When no signal is available output of sensor module goes high and transistor LED is switched ‘OFF’. When another signal arrives, LED is switched ‘ON’ and through clock pulse at Pin No. 14 of IC-3. This makes the LED to switch ‘ON’ the appliance at first pulse and ‘OFF’ the appliance at its Second pulse arrived at its sensor. Transmitter circuits works satisfactorily with 6-9V DC. Battery but receiver circuits needs 6V regulated supply. The CAMD CM8870/70C provides full DTMF receiver capability by integrating both the band-split filter and digital decoder functions into a single 18-pin DIP, SOIC,or 20-pin PLCC package. The CM8870/70C is manufactured using state-of-the-art CMOS process technology for low power consumption (35mW, MAX) and precise data handling. The filter section uses a switched capacitor technique for both high and low group filters and dial tone rejection. The CM8870/70C decoder uses digital counting techniques for the detection and decoding of all 16 DTMF tone pairs into a 4-bit code. This DTMF receiver minimizes external component count by providing an on-chip differential input amplifier, clock generator, and a latched three-state interface bus. The on-chip clock generator requires only a low cost TV crystal or ceramic resonator as an external component.
Notes:
1. dBm = decibels above or below a reference power
of 1mW into a 600. load.
2. Digit sequence consists of all 16 DTMF tones.
3. Tone duration = 40ms. Tone pause = 40ms.
4. Nominal DTMF frequencies are used.
5. Both tones in the composite signal have
an equal amplitude.
6. Bandwidth limited (0 to 3KHz) Gaussian Noise.
7. The precise dial tone frequencies are
(350Hz and 440Hz) ±2%.
8. For an error rate of better than 1 in 10,000
9. Referenced to lowest level frequency component
in DTMF signal.
10. Minimum signal acceptance level is measured with
specified maximum frequency deviation.
11. Input pins defined as IN+, IN–, and TOE.
12. External voltage source used to bias VREF.
13. This parameter also applies to a third tone injected onto
the power supply.
14. Referenced to Figure 1. Input DTMF tone level
at –28dBm.
COMPONENTS USED

RESISTANCE:
R1,            150W
R2,R11,R12    100kW
R3, R7        10KW
R4, R8        4.7kW
R5,R6,R9,R10  15KW
R13                    220K W
R14                    1KW
R15-R22           150W
VR-1,VR-2    1MW Variable Resistance

CAPACITOR:
C1,C2,C4,C5    0.1 mfd (104 pf)
C3            220 mfd
MIKE            Condensor Microphone

SEMICONDUCTOR:
IC1-               UM91215B (DTMF CODER)
IC2, IC-3        741 (OP AMP)
IC-4                    CM8870 (DTMF DECODER)
IC-5            74LS47 (DECODER)
T1,T3            NPN BC548
T2,T4            PNP BC558
LED            Light Emitting Diode
Pt.            Photo Transistor

MISCELLANEOUS:
IC Base            8 Pin (2pcs.)
Speaker            8 ohms
Optical Fibre        General purpose
PCB            General purpose
Slide Switch               DPDT
Battery            6 volt DC

CIRCUIT DAIGRAM

RECEIVER

AUTOMATION SECTION

BLOCKDIAGRAM

CONSTRUCTION AND WORKING

IR-LED: It carries signals and converted into optical signals.

PHOTO TRANSISTOR: The electrical signals are regained from the optical signals.

DTMF CODER: It is generates the DTMF signal corresponding to the number entered from the keyboard.

DTMF RECEIVER/DECODER : It is fed to DTMF decoder which gives the binary output corresponding to the signal received from the transmitter.

DEMULTIPLEXER/ 4-16 LINE DECODER:  It takes the 4 line BCD input and selects respective output one among the 16 output lines. It is active low output and drives to relay.

RELAY DRIVER : Its section controls the relay. It has a Not Gate and four NPN transistors. NPN transistor is drive to relay which works as a switching. Relay controls the AC devices.

WORKING OF AUTOMATION CONTROL SECTION:
Signal Decoding Unit:
This is the main unit of this system. This unit consists of a DTMF to BCD decoder IC MT 8870, 4 to 16 line decoder IC 74154 and hex inverter gate IC 4049. The working of all the above IC’s are mentioned here before.
The DTMF to BCD decoder IC MT8870 takes a valid tone signal from the IR transmitter section. Then the tone signal is converted in to 4 bit BCD number output obtained at pins from 11 to 14. This output is fed to the 4-16 line decoder IC74154. This IC takes the BCD number and decodes. According to that BCD number it selects the active low output line from 1 to 16 which is decimal equivalent of the BCD number present at its input pins. Since the low output of this IC the output is inverted to get logic high output. This inversion is carried out by hex inverter IC 4049- built on TTL logic. This IC inverts the data on its input terminal and gives inverted output.
3. Device switching unit:
This unit consists of a tri state buffer and a D flip flop. After making confirmation of current status of the device to alter the status of that device, you have to change the mode of the tri state buffer by making the control input high. This is done by pressing the ‘#’ key. When this key is pressed the output of the 4-16 line decoder goes low          The output of tri state buffer is latched by using a D flip-flop. Here this D flip flop is used in the toggle mode. For each positive going edge of the clock pulse will trigger the flip-flop.
After a period of 5 seconds the output of the IC 6 goes low and puts the tri state buffer in the high impedance state. Therefore to change the status of any other device is to be done after the output of IC 6 goes low, again ‘#’ key is pressed to make the tri state buffer act as input –output state and the respective code of the device is pressed.
4. Power supply unit:
For the proper working of this local control section except the local telephone set it needs a permanent back up which gives a 5V back up continuously. This is achieved by using a 5V regulated power supply from a voltage regulated IC 7805. This 5V source is connected to all ICs and relays. This IC gets a backup from a 9V battery.
5. Relay driver circuit:
To carry out the switching of any devices  we commonly use the relays. Since the output of the D flip flop is normally +5V or it is the voltage of logic high state. So we cannot use this output to run the device or appliances. Therefore here we use relays, which can handle a high voltage of 230V or more, and a high current in the rate of 10Amps to energize the electromagnetic coil of the relays +5V is sufficient. Here we use the transistors to energize the relay coil. The output of the D flip-flop is applied to the base of the transistor T2 – T5 via a resister. When the base voltage of the transistor is above 0.7V the emitter-base (EB) junction of the transistor forward biased as a result transistor goes to saturation region it is nothing but the switching ON the transistor. This intern switches on the relay. By this the devices is switches ON. When the output of D flip-flop goes low the base voltage drops below 0.7V as a result the robotic devices also switches OFF.
CIRCUIT DESCRIPTION:
This system is divided into two sections, 1: Remote Section 2: automation Control Section.
REMOTE SECTION:
This unit consists of IR transmitter section, which is present in the remote place. The figure (E) shows the circuit diagram of the DTMF encoder, which resembles the DTMF transmitter section. It uses DTMF encoder integrated circuit, Chip UM 91214B. This IC produces DTMF signals. It contains four row frequencies & three column frequencies. The pins of IC 91214 B from 12 to 14 produces high frequency column group and pins from 15 to 18 produces the low frequency row group. By pressing any key in the keyboard corresponding DTMF signal is available in its output pin at pin no.7. For producing the appropriate signals it is necessary that a crystal oscillator of 3.58MHz is connected across its pins 3 & 4 so that it makes a part of its internal oscillator.

Figure (E). Circuit diagram of the DTMF encoder

This encoder IC requires a voltage of 3V. For that IC is wired around 4.5V battery. And 3V backup Vcc for this IC is supplied by using 3.2v zener diode.
The row and column frequency of this IC is as on the fig. “B”. By pressing the number 5 in the key pad the output tone is produced which is the resultant of addition of two frequencies, at pin no. 13 & pin no.16 of the IC and respective tone which represents number ‘5′ in key pad is produced at pin no.7 of the IC. This signal is sent to the DTMF transmitter section through IR-LED.
ROBOTIC ARM CONTROL SECTION:
This is a control unit through which you can control your devices. This contains one DTMF transmitter section  and a devices Control Section. The devices to be controlled must be connected to phototransistor through control unit. Control unit is kept with a sufficient backup.
devices control Section consists of a DTMF decoder, 4-16 line decoder/demultiplexer, D-flip-flops, and relay driver circuits. Before going into detail of the circuit, we will take a brief description about integrated circuits used in local control section.
MT 8870 DTMF decoder:
IC MT8870/KT3170 serves as DTMF. This IC takes DTMF signal coming via telephone line and converts that signal into respective BCD number. It uses same oscillator frequency used in the remote section so same crystal oscillator with frequency of 3.85M Hz is used in this IC.
Working of IC MT8870:
The MT-8870 is a full DTMF Receiver that integrates both band split filter and decoder functions into a single 18-pin DIP. Its filter section uses switched capacitor technology for both the high and low group filters and for dial tone rejection. Its decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. External component count is minimized by provision of an on-chip differential input amplifier, clock generator, and latched tri-state interface bus. Minimal external components required include a low-cost 3.579545 MHz crystal, a timing resistor, and a timing capacitor. The MT-8870-02 can also inhibit the decoding of fourth column digits.
MT-8870 operating functions include a band split filter that  separates the high and low tones of the received pair, and a digital decoder that verifies both the frequency and duration of the received tones before passing the resulting 4-bit code to the output bus.
The low and high group tones are separated by applying the dual-tone signal to the inputs of two 6th order switched capacitor band pass filters with bandwidths that correspond to the bands enclosing the low and high group tones.

Figure (F).Block diagram of IC MT8870

The filter also incorporates notches at 350 and 440 Hz, providing excellent dial tone rejection. Each filter output is followed by a single-order switched capacitor section that smoothes the signals prior to limiting. Signal limiting is performed by high gain comparators provided with by stresses to prevent detection of unwanted low-level signals and noise. The MT-8870 decoder uses a digital counting technique to determine the frequencies of the limited tones and to verify that they correspond to standard DTMF frequencies. When the detector recognizes the simultaneous presence of two valid tones (known as signal condition), it raises the Early Steering flag (ESt). Any subsequent loss of signal condition will cause ESt to fall. Before a decoded tone pair is registered, the receiver checks for valid signal duration (referred to as character- recognition-condition). This check is performed by an external RC time constant driven by ESt. A short delay to allow the output latch to settle, the delayed steering output flag (StD) goes high, signaling that a received tone pair has been registered. The contents of the output latch are made available on the 4-bit output bus by raising the three state control input (OE) to logic high. Inhibit mode is enabled by a logic high input to pin 5 (INH). It inhibits the detection of 1633 Hz.
The output code will remain the same as the previous detected code. On the M- 8870 models, this pin is tied to ground (logic low).
The input arrangement of the MT-8870 provides a differential input operational amplifier as well as a bias source (VREF) to bias the inputs at mid-rail. Provision is made for connection of a feedback resistor to the op-amp output (GS) for gain adjustment.
The internal clock circuit is completed with the addition of a standard 3.579545 MHz crystal.
The input arrangement of the MT-8870 provides a differential input operational amplifier as well as a bias source (VREF) to bias the inputs at mid-rail. Provision is made for connection of a feedback resistor to the op-amp output (GS) for gain adjustment.
The internal clock circuit is completed with the addition of a standard 3.579545 MHz crystal.

74154  4-16 line decoder/demultiplexer:
IC 74154 is a 4-16 line decoder, it takes the 4 line BCD input and selects respective output one among the 16 output lines. It is active low output IC so when any output line is selected it is indicated by active low signal, rest of the output lines will remain active high. This 4-line-to-16-line decoder utilizes TTL circuitry to decode four binary-coded inputs into one of sixteen mutually exclusive outputs when both the strobe inputs, G1 and G2, are low. The demultiplexing function is performed by using the 4 input lines to address the output line, passing data from one of the strobe inputs with the other strobe input low. When either strobe input is high, all outputs are high. These demultiplexer are ideally suited for implementing high-performance memory decoders.

Figure G. IC 74154 4-16 line decoder
All inputs are buffered and input clamping diodes are provided to minimize transmission-line effects and thereby simplify system design.
TRUTH TABLE:

IC 4013 D-flip-flop:
IC 4013 is a conventional D-flip-flop IC. This IC consists of two D flip-flops. These flip-flops are used to latch the data that present at its input terminal. Each flip-flop has one data, one clock, one clear, one preset input terminals.

(Above figure shows a single D-flip-flop)

Relay driver circuit:
To carry out the switching of devices we commonly use the relays. Since the output of the D flip flop is normally +5V or it is the voltage of logic high state. So we cannot use this output to run the device or appliances. Therefore here we use relays, which can handle a high voltage of 230V or more, and a high current in the rate of 10Amps to energize the electromagnetic coil of the relays +5V is sufficient. Here we use the transistors to energize the relay coil. The output of the D flip-flop is applied to the base of the transistor T2 – T5 via a resister. When the base voltage of the transistor is above 0.7V the emitter-base (EB) junction of the transistor forward biased as a result transistor goes to saturation region it is nothing but the switching ON the transistor. This intern switches on the relay. By this the device is switches ON. When the output of D flip-flop goes low the base voltage drops below 0.7V as a result the device also switches OFF.
Power supply unit:
NEED OF POWER SUPPLY:-
Perhaps all of you are aware that a power supply is a primary requirement for the test bench of a home experimenter’s mini lab. A battery eliminator can eliminate or replace the batteries of solid-state electronic equipment and 220V A.C. mains instead of the batteries or dry cells thus can operate the equipment. Nowadays, the sued of commercial battery eliminator or power supply unit have become increasingly popular as power source for household appliances like transceiver, record player, clock etc.
Summary of power supply circuit features:-
Brief description of operation: gives out well regulated +8V output, output current capability of 500mA.
Circuit protection: Built –in overheating protection shuts down output when regulator IC gets too hot.
Circuit complexity: simple and easy to build.
Circuit performance: Stable +8V output voltage, reliable Operation.
Availability of components: Easy to get, uses only common basic components.
Design testing: Based on datasheet example circuit, I have used this circuit successfully as part of other electronics projects.
Applications: part of electronics devices, small laboratory power supply.
Power supply voltage: unregulated 8-18V-power supply.
Power supply     current: needed output current 500 mA.

Components cost: Few rupees for the electronic components plus the cost of input transformer.

Pin Diagram of 7808 Regulator IC
Pin 1: Unregulated voltage input
Pin 2: Ground
Pin3: Regulated voltage output

Component list

7808 regulator IC
2. 0-12 transformer
3. 1000uf and 100uf. Capacitor, at least 25V voltage rating.
DESCRITION OF POWER SUPPLY

This circuit is a small + 8 volts power supply. Which is useful when experimenting with digital electronics.  Small inexpensive battery with variable output voltage are available, but usually their voltage regulation is very poor, which makes them not very usable for digital circuit experimenter unless a better regulation can be achieved in some way. The following circuit is the answer to the problem.
This circuit can give +8V output at about 500mA current. The circuit has overload and terminal protection.

CIRCUIT DIAGRAM OF POWER SUPPLY
The above circuit utilizes the voltage regulator IC 7808 and 7805 for the constant power supply. The capacitors must have enough high voltage rating to safely handle the input voltage feed to circuit. The circuit is very easy to build for example into a piece of Zero board.
For the proper working of this local control section except the mobile phone  or local telephone set it needs a permanent back up which gives a 8V back up continuously. This is achieved by using a 8V regulated power supply from a voltage regulated IC 7808. This 5V source is connected to all ICs and relays. This IC gets a backup from a 9V battery.

Fig J. Circuit Diagram of Local Control Section.
USED COMPONENTS

SEMICONDUCTORS
(1) IC-1 ………  7808
(2) IC-2…………. CM8870P
(3) IC-3…………. 74154
(4) IC-5-6………CD 4013
(5) IC-4……….. 4049
(6) IC7 ………… UM 91214B
(7) D1-D2 ………….IN 4007
(8) D3…………… 3V Zener
(9) LED ……………. Light Eammiting Diode
(10) T1-T6…………..(NPN) 368
(11) Crystal ………… 3.57 Mhz.
(12) Photodiode
(13) Phototransistor

RESISTOR
(1) R1……….330K OHm.
(2) R2……….. 100K OHm.
(3) R3,R4,R7 ………. 10K OHm.
(4) R5,R6, ………. 1K OHm.
(5) R8-R12…. 100 OHm.

CAPACITOR
(1) C1…………. 1000MFD.
(2) C2,C3…………. 0.1 MFD.

MISCELLANEOUS
(1) RELAY ………………. 6V \100 0Hm.
(2) TRANSFORMER…… 0-9 (Step down)

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