long distance serial communication

[pallu87]

hii...
i am working on a project where i need to transmit serial data over a long distance approx 2 miles...on twisted copper lines(2 wires)
can you offer suggestions on how it is possible...
i googled it and found out that there are many drivers and modems for this but with insanely high prices like a 1000$

please help me out i am really stuck against a wall here....

Its a Data acquisition system
i am using avr to measure temp humidity and power and tx it via uart to a PC
there will be many avrs joining 2 the pc... i am using only 2 wires tx and gnd
no feedback needed, the problem is...
the distance between avr and pc is approx 2 km

 

[chrisshortys]

Might be worth considering going over to Fiber Optics?

 

[pallu87]

fiber optics just for 2 miles???
and i am goin 2 get only twp i.e telephone leased lines

 

[chrisshortys]

Sory, i thought you might mean that the two places where on the same site. I run fiber cables for lengths of just 120 meters at times.

 

[crutschow]

I assume you can transmit at a low data (baud) rate. This reference https://www.lammertbies.nl/comm/info/RS-232_specs.html says you can transmit to 3000 feet (900 meters) at 2400 baud. So at a lower rate (say 300 or 600 baud, maybe even 1200) you should be able to go 2km.

 

[0x00x0]

Have a look at this: https://www.commfront.com/RS232-RS485-RS422-Serial-Converters/Serial-Repeaters.htm

The RPT-232-3 is an optically isolated RS-232 data repeater (extender) (TX, RX, and GND), which works in pairs to extend the full-duplex RS-232 distance up to 1.8 miles (3 km). This product features opto-isolation circuitry, which effectively protect your RS-232 devices from transient surges, ground loop, and remote lightning.

The unit is powered from the RS-232 data line, and therefore, no external power or RTS, DTR is required.

And only $104 each

 

[arrie]

I would also go repeater.
But it's important to ensure there are nothing to add noise in the form of EMF to your signal cable, with the repeaters that can be problematic.

 

[blueroomelectronics]

Why not look at XBee extended range RF adapters.

 

[Diver300]

I would try RS 232 or RS485 direct with no repeater. If you keep the baud rate down to 1200 baud or so the capacitance and delays should not affect you.

I have used 3 V CMOS levels over 100 m at 4800 baud with no problems.

 

[blueroomelectronics]

RS232 not likely, RS485 or RS422 with proper temination and slow baud rates has a fighting chance.

 

[arrie]

Hi Bill.

Tell us more. I know that pallu specifically stated 2 copper wires.
But I'm always interested in RF, what sort of frequency are you taking about, what final stage power output, etc. for licensing purposes. Will it not be overkill?

wifi has become cheap, then there is the new(old) wireless usb standard. If he has DLOS he can also build a neat optic wireless solution. Love those.

 

[crutschow]

Have a look at this: https://www.commfront.com/RS232-RS485-RS422-Serial-Converters/Serial-Repeaters.htm

And only $104 each

I agree that, if you go with a wired connection, an isolator is a good thing to minimize transient and ground loop problems. And I believe it's $104 for the pair.

 

[Willbe]

transmit serial data over a long distance approx 2 miles...on twisted copper lines(2 wires)
Its a Data acquisition system
i am using avr to measure temp humidity and power and tx it via uart to a PC
there will be many avrs joining 2 the pc... i am using only 2 wires tx and gnd

At 30'/Ω, a 4 mile loop resistance comes out to ~700 Ω, so using a 50 v P-P 300 ohm source impedance transmitter into the sending end of 300 ohm twin lead gives ~40 mA P-P into a 300 ohm load.
What minimum bandwidth do you need? With the setup above you might get 16 kHz.