Phone and DTMF decoder

  • Thread starter php
  • Start date
  • #1
php
11
0
hi,

how does one connect a telephone line with a DTMF decoder(e.g CM8870). i.e which telephone wires(of the 2 pairs of the telephone cable) to i connect to the 8870?

again if i use a cell/mobile phone how to i connect to the 8870?

any help will be appreciated.
 

Answers and Replies

  • #2
MATLABdude
Science Advisor
1,655
4
hi,

how does one connect a telephone line with a DTMF decoder(e.g CM8870). i.e which telephone wires(of the 2 pairs of the telephone cable) to i connect to the 8870?

again if i use a cell/mobile phone how to i connect to the 8870?

any help will be appreciated.

Well, if you look at the datasheet:
http://www.cmd.com/products/data/pdf/obsolete/cm8870.pdf

...and some background on telephone wiring:
http://en.wikipedia.org/wiki/Tip_and_ring

Then you see that you'd probably need some circuitry before the CM8870 to filter out the -48V bell ringing signal, and scale the actual dial tones so that they don't exceed 5V.

For a cell phone, you'd need a microphone or an audio jack if the phone comes with handsfree capability.

Also, a Google search for 'DTMF Decoder' brings this up:
http://www.bobblick.com/techref/projects/tonedec/tonedec.html
 

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