I want to use a DTMF decoder IC such as HT9170 to get the numbers. What confused me is how to connect the decoder with telephone line? Is the transformer necessary? Or can I have another solution? What=92s the means of the =93600-600 Ohm=94 marked with the transformer? Thank you very much!
usually it is the easiest way.
yes.
resistance of the windings.
A transfomer is advisable, it will protect your electronics from the
48V on the phone line, such asmore here
martin
You can also use a pair of high- voltage capacitors (one in each line) to isolate the signal. See
JS
Please look this web lnik there are lots of telephone interface circuits.
Joe
For a hobby project or will you be selling this? The transformer or capacitor solutions will suffice for a do-it-yourself project. But if this has got to be of professional quality, I'd suggest looking up the requirements for the interface requirements. Also, consider the that requirements will differ between countries in which you intend to sell this.
I saw 'China' in your email address, so I'm assuming that whatever solution you choose may show up in millions of consumer products sold worldwide any time now. :-/
s/resistance/impedance/
Cheers! Rich
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