telephone remote control

8/14/2019 Telephone Remote Control

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telephone remote control

introduction

telephone remote control implies control of devices at a remote

location via a circuit interfaced to the remote telephone line/device by dialing

specific dtmf ( dual-tone multi frequency) digits from a local telephone. the

telephone remote system described here has the following features.

1) it can control multiple channels/relays.

2) it provides you feedback when the circuit is in energized state and also

sends an acknowledgement indicating action with respect to the switching

on of each requested relay and switching off of all relays (together).

3) it can selectively switch on any one or more relays one after the other and

switch off all relays simultaneously.

govt. poly. washimh 1


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the telephone remote control

to all stage



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h = high, l = low.

connected. in a short while you will hear a musical note indicating

that the circuit connected to the remote telephone is active.

2. now if you want to switch on a particular relay/device, press * button on the

telephone keypad followed by any one of digits 1 to 7 corresponding to the

device/relay number that you desire to switch on. the switching on of the relay

will be acknowledged/indicated by a musical note. now you may keep the handset

on the cradle.

3. if you want to switch off the relays, press * and then press key for digit 8. a

musical note is heard, which indicates that all the relays have been switched off.

keep the handset on cradle.

the circuit

at the remote telephone end, the ringing signal is detected by a high-

input-impedance op-amp ca3140e that is wired as a comparator. since this op-amp

output is open-collector type, the output pin has been pulled towards vcc via 10-

kilo-ohm resistor r21. ic2 (ne556) comprises two timers (ne555 type) that have

been configured as monostables.



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when a ring is detected by ic1, its output triggers one of the timers in

ic 556. the output of the timer after inversion by one of the nand gates of ic3

(cd4011), enables ic4 (cd4060) by taking its reset pin 12 low. (ic4 is an

oscillator-cum-14-bit binary counter.) as a result, ic4 starts counting when the ring

signal strikes the input of the circuit.

after some time, decided by the setting of preset vr3, q12 output of

ic4 goes high. this output coupled to pin 8 of a nand gate inside ic3 will enable

it. the detected ring signal (if the ring signal is still persisting) applied to pin 9 of

the same nand gate (after inversion by another nand gate) will pass through it to

trigger the second monostable inside ic2 (ne556) as well as ic5 (ne555), which is

again wired as a monostable. this arrangement avoids the circuit from being

triggered by any transients or false ring signals on the telephone line.

the output of the second monostable of ic2, available at its pin 9,

drives transistor t2 and shunts the telephone line with 220-ohm resistor (r20). as a

result, the telephone line voltage drops to around 10 to 12 volts. this is equivalent

to the lifting of the telephone handset of the remote telephone. as mentioned

earlier, both ic5 and the second monostable of ic2 are triggered simultaneously.

the output of monostable ic5 starts melody generator ic6 (um66) and the musical

note obtained from it is coupled to the telephone line. this informs the caller that

the remote circuit is in energized condition, the next step for the operator at local



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telephone is to press the * button, which makes the local telephone to operate in

the tone-dialing mode. the digits that are pressed after pressing the * button are

converted to dtmf tones.

the tone is decoded by ic7 and its three lsbs (covering binary

equivalent of decimal digits 0 through 7) are connected to the address inputs,

while the msb line is connected to reset pin 2 of ic8 (cd4099, an 8-bit addressable

latch). when a valid dtmf tone is detected at the input of ic7, its pin 15 goes high

to enable ic8 after inversion by nand gate of ic2. at the same time, it triggers ic5

for informing the caller that his key-press is accepted. numbers 1 to 7 on the local

keypad cause latching of the corresponding relays, while number 8 causes reset

operation, which means that we can switch on seven relays independently one by

one and switch off all relays simultaneously by pressing number 8. the output of

ic8 drives the relays via the relay driver transistor. truth table i(a) and i(b) of

cd4099 indicate relay operation.

allignment

1. connect the circuit to the telephone line.

2. adjust preset vr1 so that the ringing pulse causes led1 to flicker. for better

performance, set the voltage at pin 3 of ic1 at approximately 2 volts.

3. the time required to activate/energize the circuit. is adjusted by preset vr3

with the help of led2

.



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4. the time available for remote switching action can be set by preset vr2 with

the help of led4. indirectly, the setting of preset vr2 determines the charge

that will have to be paid to the telecom department.

5. the period of musical note can be controlled by the adjustment of preset vr4

with the help of led3.

IC CM8870 DTMF DECODER

PIN DESCRIPTION

in+ 1 18 vdd

in - 2 17 sugt

gs 3 16 est

vref

4 15 std

ic

ic 5 14 q4

cm 8870

ic 6 13 q3



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osc 1 7 12 q2

osc 2 8 11 q1

vss 9 10 toe

pins name description

1 in+ non-inverting op-amp input

2 in-inverting op-amp input

3 gs gap select. gives access to output of from end differential

amplifier for connection of feedback resistor.

4 vref reference voltage output nominally vob is used to bias inputs at

measure see f 2).

5 ic internal connection must be tied to vss

6 ic internal connection must be tied to vss

7 osc1 cock input.

8 osc2 cock output. a 3.5795 mhz crystal connected between osc1 and

osc2 completes the internal oscillator circuit.

9 vss negative power supply input

10 toe 3-state output enable (input) logic high enables the outputs q1-

q4 internal pull cd

11-14 q1-q4 b-state data outputs. when enabled by toe, provide the code

corresponding to the last valid tone-pair received (see fig.5)

15 std deaved steering output. presents a logic high when a received

tone par has been registered and the output latch updated;

returns to logic low when the stage on sugt falls below vrs;



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16 est early steering output. presents a logic high once the digital

algorithm has detected a valid tone pair (signal condition).any momentary loss of signal condition will cause est to return

to a logic low.

17 sugt steering input/guard time output (bi-directional). a voltage

greater than detected at st causes the device to register the

detected tone pair and upcare the output latch. a voltage less

than vrst frees the device to accept a new tone pair. the gt

output acts to reset the external steering time-constant; its state

is a function of est and the voltage on st.

18 vdd

positive power supply input.



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pcb layout



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features

1) it can control multiple channels/relays.

2) it provides you feedback when the ckt.is in energized state and also sends

an acknowledgement indicating action w.r.t. the switching on of each

requested relay and switching off of all relays.

3) it can selectively switch on any one or more relays one after the other and

switch off all relays simultaneously.

4) it can control timing devices such as water heater, water pumps, air

conditioners washing machines, microwave ovens etc.

5) through this equipment we can controy timing devices such as heater,

water pump, a.c. (air conditioner), washing machine, etc.

6) if we forget to switch off any device, we can switch it off from outside

without returning to home. so the device can be protected from being

damaged.

7) we can switch on the devices such as microwave ovens or heaters if we are

coming to home. this system can be misused by outsiders to know the

about this system easily so to overcome this problem an electronic lock can

be used for security.



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advantages

1) we can control appliances from any distance.

2) easy to operate.

3) electricity can be saved using this ckt.

4) cost is less.

5) no.of channels controls by this system.

applications

1) it can be used in homes, for controlling heaters, light pump motors or what

your it may be.

2) it can use in conference to control light, a system on easy control device.

3) it is also applicable for industries to controlling machines, an any system by

the telephone on mobile.

4) it can control the electrical appliances from any distance.

5) it can be used in industries, markets, homes, offices.

6) we can save electricity using this ckt.

7) this equipment is not hazardous to any body specially children.

8) any body can operate it easily ( technical knowledge is not essential ).



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users manual

1) dial the number of the remote telephone to which the ckt is connected, you

will hear a musical note indicating that the ckt is active.

2) press * button followed by any one of digits 1 to 7 corresponding to

device to switch it on.

3) the switching on of the relay will be indicated by a musical note. they you

may keep the handset on the cradle.

4) press * button followed by digit 8 to switch off all the devices.

5) a musical note is heard, which indicates that all the relays have been

switched off. keep the handset on cradle.

specifications

1) supply vtg : +9v

2) power consumption : 5w

3) current requirement : 1a.



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parts list

semiconductors :

ic1 - ca3140e op-amp

ic2 - ne556 dual timer

ic3 - cd4011 quad nand gate

ic4 - cd4060 14-stage counter/oscillator

ic5 - ne555 timer

ic6 - um66 melody generator

ic7 - cm8870 dtmf-decoder

ic8 - cd4099 8-bit addressable latch

ic9 - 7805 regulator +5v

t1 - bc548 npn transistor

t2-19 - bc547 npn transistor (only t2 and t6 shown)

led1, led2 - green led

led3 - yellow led

led4 - red led

d1, d2 - in4148 switching diode

d3-d10 - in 4007 rectifier diode (only d3 and d4 shown)

resistors (all -watt, 5% carbon, unless otherwise stated)

r1, r16, r17 - 150-kilo-ohm



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r2, r21 - 10-kilo-ohm

r3 - 33-kilo-ohm

r4 - 680-kilo-ohm

r5 - 560-ohm


r7 - 1-mega-ohm

r8, r15 - 390-ohm


r11 - 270-ohm

r13, r14 - 3.3k-kilo-ohm

r18 - 330-kilo-ohm

r19, r22-r27 - 4-7-kilo-ohm (r22-r27 not shown in the figure)

r20 - 220-ohm

vr1 - 10-kilo-ohm preset

vr2 - 1-mega-ohm preset



capacitor :

c1 - 0.22f ceramic disk

c2 - 0.220f, 10v electrolytic



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c4, c5, c8 - 0.01f ceramic disk

c6, c11, c12 - 0.1f ceramic disk


c9 - 0.02f ceramic disk

c10 - 0.47f, 100v polyster

miscellaneous :

xtal - 3.58mhz crystal

rl1-rl7 - 6v, 150-ohm ic/o relay (only rl4 shown)



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conclusion

the telephone remote control is very useful in future fast and advance

life. through further improvement we can control the appliances by giving timings

with the use of micro controllers and computers.

this application is very useful in industry where the energy

consumption per second is very large so that the product cost can be reduce. also

it can help to solve the problem of electric power deficiency.

the total cost of "the telephone remote control system" came up to

rs.500/-. this is a reasonable cost as the efficiency , reliability and safety to control

home appliances.


telephone remote control

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