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Power and Data over 2 wires

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christophercowler

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Hi,

I have a requirment to send power and data over a single pair of wires and am experiancing problems, here are my requirements:

Limited to 2 wires
Distance is 300 meters
Minimum baudrate required is 1200bps
Power is 24VDC @ 1amp (could make it 24VAC if needed)

I was thinking this could be done by coupling power onto a half duplex RS485 link. Some experimentation has shown this to be difficult, further research and digging around on the net has uncovered a few other people who have attempted the same thing but failed.

If anyone has any suggestions on how I might achieve this I would be most greatful.

Thanks

Chris
 

Hi

Use a low ohm resistor (10 ohm or less) in series with the + line
connect a short switch (best on power mosfet + driver ) after the resistor between the + and Gnd.(shorting the PSU when conducting)
the resistor is power limiting and for avoid shorting the power supply

Connect a current sense amplifier (INA138) on the other end of the GND

connect the uart TX line to the MOSFET driver input
at the other end connect the INA138 output to the RX line

All the best

Bobi
 
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