KT3170 Vs. MT8870 DTMF Decoders

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vinod
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KT3170 Vs. MT8870 DTMF Decoders

Post by vinod » Sat Feb 13, 2010 6:11 am

Does there exists any differences in the decoding response of KT3170/MT8870 DTMF Decoders ?.
I am using MT8870 and have no capability to detect DTMF tones on on-hook state.
But somewhere (http://electronicsworld.tripod.com/remo ... sckt2.html) I have read about KT3170 is that,
Once a call is established (after hearing ring-back tone) on on-hook, if you dial ‘0’ in DTMF mode
KT3170 can decodes this as 1010 without attending the call.

If digit ‘0’ is not dialed (in DTMF) after establishing the call, the ring continues
and the telephone connected in parallel can be used for normal conversation.

If this is true I can simplify my DTMF project by replacing MT8870 with KT3170. In the case of MT8870 I have
to design complex ring detection circuit to automatically off-hook.


Many peoples obtained positive result by following the circuit in the above link using KT3170.
My phone-set have no caller id facility. Does there any possibility for the caller ID (CLIP) signal to come ?
Which mode is used to send caller information in India (FSK or DTMF). If it is DTMF, I think DTMF Decoders can detect DTMF tones on on-hook state.
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Re: KT3170 Vs. MT8870 DTMF Decoders

Post by dyarker » Sat Feb 13, 2010 6:58 am

Which phone? Near end (the phone line with your circuit attached), or far end (a phone on another line)?

If near end, your circuit will "hear" dtmf tones. If calling from far there is no connection through the switch.
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Re: KT3170 Vs. MT8870 DTMF Decoders

Post by SETEC_Astronomy » Sat Feb 13, 2010 8:56 am

vinod wrote:Does there exists any differences in the decoding response of KT3170/MT8870 DTMF Decoders ?.
I am using MT8870 and have no capability to detect DTMF tones on on-hook state.
You cannot decode DTMF with the phone on-hook. The call has NOT been established until you lift the phone therefore no audio is passed to your line yet.

In the states CallerID is sent using Bell 202 FSK and can be decoded with the phone on-hook, the data is sent only once in between the first and second rings. If your phone doesn't have the ability to receive CallerID you can buy a device or IC to do so but you must also purchase the service from your telco.

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