Inject sound to a phone landline

[AnalogKid]

Is the source really 0.6 mV (600 uV) or is that a typo? What is the source? What is the output voltage at normal volume levels? What is the current capability? Is it a speaker output from a small amplifier, the line output from a computer, the earphone output from an MP3 player - what?

Your drawing implies that you want to inject audio while the handset still is connected to the phone instrument. This is harder to do than just replacing the handset with an audio source. Which do you want to do?

ak

 

[kellygoose]

You say home phone line. Is it post?(plain old telephone system). Or is it VOiP? The difference is significant on how you build your system. I worked for AT&T for many years as a technician working on problems similar to what you are asking, please let me know if I may be of help.

 

[linningck]

Hi kellygoose. It is not VOIP. It is to send basic sound through basic phone and basic landline.
You are welcome to help.

 

[linningck]

Here is the idea, plug my mobile between handset and phone to send sound (music, speech...) by phone landline.

 

[linningck]

Source is 0.6 v, sorry for mistake ;-)
And, yes it must be isolated as source is not protected against input signals.

 

[CDRIVE]

You say home phone line. Is it post?(plain old telephone system).

Uh,.. I think that would be "POTS".

Chris

 

[AnalogKid]

Here is the idea, plug my mobile between handset and phone to send sound (music, speech...) by phone landline.

What is the "iso ampli"? If this is an opamp, a small audio amplifier with speaker outputs, an MP3 player, or what?

Whatever it is, we can figure out how to couple it to the handset jack on the phone. All of your drawings show a connection to the micropphone in the handset, but this will not work. The plan is to completely remove the handset mic, and inject your audio into the handset jack on the phone.

ak

 

[linningck]

Here, is why I request help. Analogkid, if you have idea, you are welcome to explain.
Iso ampli is because phone landline voltage is far to high for a mobile.

 

[AnalogKid]

Here, is why I request help. Analogkid, if you have idea, you are welcome to explain.
Iso ampli is because phone landline voltage is far to high for a mobile.

If you were injecting directly into the phone line that would be true, but the circuit already shown would work for that. But the high line voltage does not appear at the handset jack, so the only requirements are low DC voltage isolation and adjusting the audio level to match what the phone wants to see.

If the music source is an MP3 player, you will need two resistors and one capacitor. The two resistors attenuate the output of the MP3 player to match the input voltage requirement of the handset jack, and the capacitor blocks the small DC voltage present at the jack for an electret microphone in the handset.

From the output of the player, a 10 uF capacitor and,a 22k ohm resistor in series, and a 2.2K resistor to GND. GND in this case is the return to the MP3 player and the microphone inout -. The junction of the two resistors goes to the microphone input +. This attenuates the audio output by 11:1, a reasonable starting point to determine what is really needed.

I'm not where I can draw a schematic. Draw one and post it and we'll move on from there.

ak

 

[linningck]

Sure, I will draw. But, what do you mean by the "circuit already shown". Many were draw.