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HT9200B DTMF generator INTERFACING TO TELEPHONE LINE

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mc004

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ht9200b

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.(**broken link removed** ) But there are 3 undefined transistor. What kind of transistors must be used in this circuits. thanks.
 

dtmf generator

This circuit from your link looks "suspicious" ..
Here is a circuit that works .. see picture below ..

Regards,
IanP
 
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    tpetar

    tpetar

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ht9200 fail

I had the same problem. I hope IanP's solution works... Anyone tried it already?[/quote]
 

hardware dtmf generator

PNP - 2N5401,
NPN - 2N5551
 
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    davehj

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ht-9200b

hi

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

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dtmf generator circuit

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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