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charkhkar
Joined: 30 Apr 2006
Posts: 2
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 08 May 2008 16:27 A circuit to make a black list for telephone |
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I wanna a simple circuit when you dial a special tel number on your phone, the connection cannot be held. To say it more simpler the circuit should allow us to lock some outgoing tel numbers, like a outgoing black list numbers! does any one have any idea? i'm not familiar with telephone systems and i have no idea to start from where 
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Eugen_E
Joined: 29 Nov 2004
Posts: 317
Helped: 30
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| 08 May 2008 18:52 Re: A circuit to make a black list for telephone |
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I guess it's for a classic (wired) telephone. In this case you need a DTMF receiver (MT8870 or other), a microcontroller (AVR/PIC/8051...), a transistor and a relay.
The relay contacts should be connected in series with the telephone.
When the number is dialed, the uC reads the DTMF receiver and if the number it's not accepted, it will activate the relay and disconnect the telephone. This has the same effect like putting the receiver on hook and abandoning the call. After this, everything is reseted to the initial state.
In some countries it's illegal to connect homemade circuits to the public telephone system.
Last edited by Eugen_E on 08 May 2008 19:41; edited 1 time in total |
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umery2k75
Joined: 19 Apr 2006
Posts: 228
Helped: 19
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| 08 May 2008 19:31 Re: A circuit to make a black list for telephone |
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| You can solve your problem as Eugen_E has mentioned, you need to have knowledge for these things.
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charkhkar
Joined: 30 Apr 2006
Posts: 2
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| 08 May 2008 20:32 Re: A circuit to make a black list for telephone |
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| thank you Eugen_E, actually i'm a newbie. I try to make my hands on the circuit, thank you for your help
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nandhu015
Joined: 11 Feb 2006
Posts: 333
Helped: 26
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| 09 May 2008 14:58 Re: A circuit to make a black list for telephone |
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Better use MT8888. It can both receive and dial dtmf codes.
But you need knowledge about any one of the micros to ineterface it
Better luck
Nandhu
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