Telephone Remote Control

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.

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the telephone remote control

to all stage

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the telephone remote control

operation instead of straightway proceeding with the circuit description, we shall start with the operation as this would help us in understanding the circuit better. the operation is as follows : 1. from the local telephone, dial the number of the remote telephone to which the circuit i table - i (a) input a2 l l l l h h h h

a1 l l h h l l h h

a0 l h l h l h l h

output qn = addressed q0 q1 q2 q3 q4 q5 q6 q7

table – i (b) wr

r

q

q

l l

l h

addressed = data = data

un-addressed hold l hold l

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the telephone remote control

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 highinput-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 10kilo-ohm resistor r21. ic2 (ne556) comprises two timers (ne555 type) that have been configured as monostables.

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the telephone remote control 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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the telephone remote control 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 . govt. poly. washim

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the telephone remote control 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 vr 4 with the help of led3.

IC CM8870 DTMF – DECODER PIN DESCRIPTION in+

1

18

vdd

in -

2

17

sugt

gs

3

16

est

15

std

14

q4

13

q3

vref

4 ic

ic

5 cm 8870

ic

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the telephone remote control osc 1

7

12

q2

osc 2

8

11

q1

vss

9

10

toe

pins

name

description

1

in+

2

in-

non-inverting op-amp input 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 q1q4 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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the telephone remote control

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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

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positive power supply input.

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the telephone remote control

pcb layout

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the telephone remote control

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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the telephone remote control

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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the telephone remote control

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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the telephone remote control

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 ¼ -watt, ±5% carbon, unless otherwise stated) r1, r16, r17

-

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150-kilo-ohm

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the telephone remote control r2, r21

-

10-kilo-ohm

r3

-

33-kilo-ohm

r4

-

680-kilo-ohm

r5

-

560-ohm

r6, r10

-

22-kilo-ohm

r7

-

1-mega-ohm

r8, r15

-

390-ohm

r9, r12

-

15-kilo-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

vr3

-

220-kilo-ohm preset

vr4

-

470-kilo-ohm preset

c1

-

0.22µf ceramic disk

c2

-

0.220µf, 10v electrolytic

capacitor :

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the telephone remote control c3

-

0.100µf, 10v electrolytic

c4, c5, c8

-

0.01µf ceramic disk

c6, c11, c12 -

0.1µf ceramic disk

c7

-

0.10µf, 10v electrolytic

c9

-

0.02µf ceramic disk

c10

-

0.47µf, 100v polyster

miscellaneous : xtal

-

3.58mhz crystal

rl1-rl7

-

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

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the telephone remote control

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.

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