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Data and DC power over a single twisted pair cable

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seven_segment

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Hello all. I'm searching for a way to transfer both data AND power over a single twisted pair cable. The data itself is a differential RS485 signal from a PIC micro and DS75176 at either end, running at 19200bps. The power is DC 24v, with a maximum current in the area of a couple of Amps.

I've never tried to do this before and searching the internet has revealed nothing, perhaps I'm just not looking in the right places? As usual, all advice/links/circuits much appreciated!

Matthew
 

Re: Data over DC power

Hi,

With low power load you can sink power from RS-485 line. You need diode and capacitor.
 

Re: Data over DC power

You can use the same line for both DC and AC/pulse signals/power, just use capacitors for separating different signals.

nguyennam
 

Re: Data over DC power

a way to transfer both data AND power over a single twisted pair cable. The data itself is a differential RS485 signal

You can't do that, as RS485 signal is BALANCED SIGNAL (differential)!
On USB connection, 2 cables for BALANCED SIGNAL data line, 2 cables for power line.
 

Re: Data over DC power

budhy said:
You can't do that, as RS485 signal is BALANCED SIGNAL (differential)!
On USB connection, 2 cables for BALANCED SIGNAL data line, 2 cables for power line.

That was my initial thought too, but on reflection I realised that its actually common practice in the audio world with 48v phantom power on balanced microphones - AFAIK 48v is applied to both the hot and cold side of the balanced line, and grounded via the screen of the cable. I'll be using STP cable for this project, so there's no reason I couldn't use a similar system, I'm just not sure how to implement it or if I'll be able to get the current rating I require?
 

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