Phone line audio interface

with this simple device, you can connect audio recorder, speaker or anything else to telephone line (input AND output). It can also be used to transfer audio over your house's phone wiring.

Step 1 Parts

You will need:
  1x phone cable (cut in half)
  1x audio cable (also cut in half)
  2x 10uF capacitor
  1x 10K resistor (approx.)
  something to mount components on

(EDIT: [Mar 19, 2011] look at the schematic for correct version)

Comments

[gitanojr]

ok there's two 1uf capacitor and one 10K resistor, what are the two 4.7k and the 2 V something???

Here is what im trying to do, i made a mic out of a phone headset using one instructable from here...

I tested the mic and worked, i cut the wire in half and added one RJ11 connectors to each end, but when i connected one end to my pc and the other end to another jack i hear a lot of noise...

Im trying to use your instructable and i believe it can be done, i attached a little drawing of what im trying to do...

Thanks...

[caitlinsdad]

What happens when a call comes in? Does it blow out what is connected?

[nodoubtman]

Is it a zener 2v ? i cannot find zener diode 2v so can i use zener diode 2.7v?

thanks! :)
marC:)

[caitlinsdad]

dunno. you have to reply to the others that are more knowledgeable in electronics to tell you.

[MikB]

Quite probably. And for bonus effects, it may well eject the contents of the two capacitors too.

10uf is unnecessarily large for passing just audio. No voltage spec is given (ringing voltage can be 100-200v depending on your country, never mind any surges for lightning). You might want to use more suitable capacitors (400v non-polarity concious ones). Oh, and that 100-200v being AC will pass straight through those capacitors. Eek.

There's also no electrical isolation between the phone line and the recorder (which if it's either mains powered, or connected to any other mains powered equipment will cause interesting noises on the line).

You are missing at the very least an isolation transformer and some diodes (back to back reverse parallel on the OUTPUT side of the transformer) to clamp the signal levels down to something normal.

It's simple, it may work, but I'd not connect anything to the line that way!

[crtn2]

Thanks.

I made this for my local phone line (not for landline), which is more safe. I will fix the schematic to be safe to connect to landline.

BTW, if i use isolation transfromer, the audio is very quiet.