Connect Telephone Line to CM8870 DTMF Decoder

[php]

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.

 

[MATLABdude]

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

 

[oswaler]

Hello,

To connect a telephone line to a CM8870 DTMF decoder, you will need to connect the telephone wires to the appropriate pins on the decoder. The CM8870 datasheet should have a pinout diagram that shows which pins correspond to the telephone line inputs. Typically, the telephone wires will be connected to pins labeled "IN+ and IN-". As for using a cell/mobile phone, you will need to connect the phone's audio output to the IN+ and IN- pins on the decoder. This can usually be done using an audio cable with the appropriate connectors. As always, it is important to consult the datasheet for the specific decoder you are using to ensure proper connection and functionality. I hope this helps. Best of luck with your project.