Communication over DC power line

[kamalpathi]

Hi,

I am trying to send DTMF signal over 24V DC power line, but as soon as i connect dtmf tone output to 24V DC bus, signal becomes dead. ie, singnal is not passing over the power line.

Pls anybody suggest some idea how to pass dtmf signal over DC power line?

Regards,
Kamal

 

[JimB]

Exactly the same as the reply I gave to this thread:

https://www.electro-tech-online.com/threads/how-can-i-send-audio-dc-suply-by-2-wires.89711/


You need to decouple the power and signal.
A good PSU will kill any signals on its output due the the action of the decoupling and smoothing capacitors. Same for the power decoupling capacitors in the amplifiers.

Modify your diagram as I have shown below.

The chokes let the DC supply pass through, but block the audio signal.
The capacitors pass the audio signal but block the DC supply from entering the amplifiers.

JimB
Attached Thumbnails

 

[RadioRon]

Another way is to wire a transformer into the DC circuit so that the transformer secondary is in series with the DC line and the primary is fed from a high powered audio amp that passes the DTMF. The secondary windings have to be able to tolerate the DC current without saturating, so you have to use a substantial power transformer. Perhaps an 8 ohm speaker driver transformer, or a 6.3 Volt filament transformer would work. I'm not sure exactly which one would be best.

This approach puts the audio source in series with the DC source instead of in parallel, so you don't shunt the audio output of the DTMF nearly so badly.