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HT9200B DTMF generator.

 
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mc004



Joined: 29 May 2006
Posts: 3
Post15 Oct 2006 16:06   HT9200B DTMF generator.
I design DTMF generator with HT9200B. But how can I interface the output of the HT9200 device to the telephone line? there is a schematic in HOLTEK web site.(http://www.holtek.com.tw/english/tech/faq/telecom_faq.htm#3-4 ) But there are 3 undefined transistor. What kind of transistors must be used in this circuits. thanks.
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IanP



Joined: 05 Oct 2004
Posts: 6306
Helped: 1474
Location: West Coast
Post16 Oct 2006 3:19   Re: HT9200B DTMF generator.
This circuit from your link looks "suspicious" ..
Here is a circuit that works .. see picture below ..

Regards,
IanP

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citofonoremoto



Joined: 03 Nov 2006
Posts: 1
Post03 Nov 2006 21:31   Re: HT9200B DTMF generator.
I had the same problem. I hope IanP's solution works... Anyone tried it already?[/quote]
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sensor_ua



Joined: 11 Oct 2006
Posts: 19
Helped: 1
Post28 Nov 2006 18:59   HT9200B DTMF generator.
PNP - 2N5401,
NPN - 2N5551
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sabeti_1990



Joined: 16 Nov 2007
Posts: 65
Helped: 4
Post25 Jun 2008 7:36   Re: HT9200B DTMF generator.
hi

NPN 2n5551 is ok
PNP 2n5404 or mpsa92 (U can use)
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rogerynt



Joined: 06 Mar 2007
Posts: 109
Helped: 11
Post30 Jun 2008 18:56   Re: HT9200B DTMF generator.
One transistor is MPSA92, the other one is MPSA42 and both of them MUST use high voltage type transistors. Otherwise the NPN transistor will switches on when ring signal applies to it, as a result the isolation fails.
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