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Please help on "Telephone voltage levels".


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Hi,
I am planning a project to control (on/off) various home appliances via telephone. I think that telephone line offers 3 different voltages for following conditions:
1-telephone not in use
2-telephone ringing
3-telephone telephone in use (i.e. eg. when receiver is picked)

The controlling will take place by the (caller)person dialling requisite number to perform a specific action. How to detect which no. is pressed?

4-Hence the corresponding vtg levels would also be required.

5-Internal hardware circuitary of a telephone would be an added advantage.

Please give me the values of above mentioned vtg. levels and link/pic of the telephone ckt.

Thanks in advance.

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In North America and in Europe we use DTMF touch-tones for dialing. Then a touch-tone decoder IC is used to give an output for each digit that is dialed.
I have no idea if DTMF touch-tones are used for dialing in India. Ask people in India.

You also need a circuit to detect that the phone line is ringing then the circuit will answer each call.

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In India also same DTMF signals are used. You can use a DTMF decoder IC to get BCD equivalent to the key pressed by the caller.

When phone line is not used its voltage will be 50V DC,
when it rings 50V AC will be applied by your exchange,
when you pick up the phone its arround 12-16V across your phone.

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