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dtmf encoder/dtmf generator

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highlander11

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I am searching for a tdmf IC which creates the dtmf tones of numbers ..
I found a lot of ICs but which is better/reliable ?

+ I need some kind of interface circuit between telephone line to the IC since if I ll connect him dirrectly he will fry (min 40 v lol)

thanks in advance,
 

nikhilele

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Other DTMF Tone Generator or dialer, NTE1690, TCM5589N, TP5089N (NEETRON Sim Lim Tower #B1), 5088, 4089 (YH Radio Sim Lim Tower #B1), LC7366


DTMF Tone Generator + Decoder, 8888, 8889, 8880, HT9170C
 

highlander11

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thanks alot BUT I still have a question
I need some kind of protection between the output of tones at the IC and the telephone line since a 40V or 150V at a IC will fry it like French Fries :)

do you have an old book or a link for the part of the DMF generator maby there .there is an protection circuit ..
since I saw a protection interface but I do think it will work ,maby I am wrong but...its a weird protection cicuit

link:
2pyw45d.jpg


+ direct connect to the line isnt an healthy choice maby a C||R + R+2 zener+ridge diode + optocoupler ?
the only problem is that what I wrote in the above line is a RING detector which I know that works since I tested it but I am not sure it will work for the opposite action of Encoding
 

tyty123

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I found a simple diagram of a modem.
Maybe the analog input circuit can give you some idea.

 
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Nick C.

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any chance someone could help me out ?

The 'correct' way to interface with the phone system, at least in the USA, is to use a Data Access Arrangement (DAA) Module. These devices are usually pre-approved by the FCC, which is a big plus if you are building something that will be sold in the US.

Google that term and you'll find many sources for these interface modules. One popular manufacturer is Cermetek.
 

highlander11

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I ll probably use TCM5589N, TP5089N



I have an idea but still not sure ..
I ll connect a spdt RELAY and a 200 ohm~300 ohm resistor to the telephone line
the relay will be controled by a microproc 8051 ( for example)
so when the microproc detects a connection of telephone line to the socket it will connect 200 ohm resistor therefore he TDMF IC wont be fried..sicne the telephone company drops the voltage to around 5 voltage when you put a 200~300 ohm resistor and fromt here on the project will dial or what ever..

will it work since it seems too simple a relay and a resistor .
since a protection circuit could make life harder
 

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