jcb@loral.UUCP (Jay Bowden) (09/20/89)
I am looking for cheap ways to extend RS-232 signals to
go about 2-3 km. I've seen no-power-needed plug-in
drivers from Black Box, but they are about $90 per side,
and that seems excessive. Anyone know of a cheaper
soloution?
THanks!
- Jay
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Jay Bowden, EE/Consultant; see also Bowden Engineering
Currently contracted at Loral Instrumentation, San Diego
{ucbvax, ittvax!dcdwest, akgua, decvax, ihnp4}!ucsd!loral!jcbkaufman@Neon.Stanford.EDU (Marc T. Kaufman) (09/21/89)
In article <2395@loral.UUCP> jcb@loral.UUCP (Jay Bowden) writes: >I am looking for cheap ways to extend RS-232 signals to >go about 2-3 km. I've seen no-power-needed plug-in >drivers from Black Box, but they are about $90 per side, >and that seems excessive. Anyone know of a cheaper >soloution? I 'invented' one of these things in 1980, and at the time my company was building them the all-up cost to manufacture, INCLUDING the external plug-in transformer AND packaging, was $5.00 So, to make it easier for the rest of you, here is a circuit that will extend a full duplex RS-232 circuit on 2 wires. Use a fast slew-rate op-amp for best results at high speed and long range. (the op amps need to be fed with +/- 12 volts, or whatever your RS-232 chips use. you can derive this from the other pins, such as RTS and DTR, or just supply it from outside): |\ TxD-------|+\ 2 K | \-------+--/\/\/\/--+------------------line + (to other line+) Gnd---+---|- / | | (0V) | | / 2K > | |\ | |/ < +----|+\ | | | \------- RxD | +----------------|- / | | | / | 1K > |/ | < | | +--------------+------------------------------line - (to other line -) As you can see, the thing is basically a DC bridge. I have run this circuit at 19.2 KB on 2 miles of wire. Have fun with it. Marc Kaufman (kaufman@Neon.stanford.edu)