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Power and data by two wires

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togarha

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Hi!

I want to send data and power supply by two wires up to 100m.

- Power supply must be 5V in remote system, it can be bigger by the two wires and regulated by an 7805 or similar in remote.

- Data is preferable to be RS-485...

How can I make the two systems? What max baudrate can I have?

Thanks in advance,

Regards,
 

umup said:
RS485 can't use 2 wires, minimum 3 (without power).
Click to expand...

Are you sure what are you talking about? I think no, RS-485 (Half-duplex) only uses 2 wires ( A , B ). It no needs more wires, it's a balanced transmission...

But, RS-485 is not necessary, can be any protocol that can send data up to 100m in the same wire that vcc...

Regards,
 

Are you sure what are you talking about? I think no, RS-485 (Half-duplex) only uses 2 wires ( A , B ). It no needs more wires, it's a balanced transmission...
Click to expand...
Yes, it will work without ground connection, but it is recommended always connect ground together :
**broken link removed** :
Signals A and B are complementary,but this doesn’t imply that one signal is a current return for the other. RS-485 is not a current loop. The drivers and receivers must share a common ground. This is
why “two-wire network” is a misnomer when applied to RS-485.
Click to expand...

You asked :
I want to send data and power supply by two wires up to 100m
Click to expand...
. Power and signal transmission usually done with 4-20mA current loop, HART used for digital data transmission through analog current loop
 

But I suppose that HART needs more extra components than other protocols that can be implemented...

I'm not sure of that, but I think so...

about the three wires, connecting the gnd wire of the two systems can make an error, it is better to put an opto-isolator than short the two grounds...

Regards,
 

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