At 03:17 PM 6/18/2007, Jim Brown wrote:
>On Mon, 18 Jun 2007 14:37:50 -0700, Jim Lux wrote:
>
> >Actually.. I think it would be better to make the "power handling"
> >wires the short ones, and the "information handling wires" (the RS232
> >connection) the long one. Rather than try and develop and build 8
> >drivers (2 coils for each of 4 steppers), just buy an off the shelf
> >long distance serial connection.
>
>Jim, you may have hit the nail square on the head (as usual)! If the
>StepIR will work that way from a user interface point of view (that is, if
>the user controls aren't on the box that you want to move to the base of
>the tower), that makes a lot of sense. RS232 will easily go several
>hundred feet if low capacitance twisted pair (like CAT5) is used for each
>circuit and the wiring avoids pin 1 problems and hum loops. Follow the
>instructions in my RFI Tutorial, and be careful NOT "ground" the RS232
>signal at more than one point. A good way to do this is to keep it off of
>ground at the tower, and let it get its power from the shack.
>
>http://audiosystemsgroup.com/RFI-Ham.pdf
>
>If you want to go further, B&B Electronics (google to find them) has good
>interfaces at moderate cost that convert the RS232 signal to a balanced
>one.
Or, if the rates are slow, my current favorite scheme is to use some
opto isolators at both ends of the line. The TxD from the controller
goes to the LED in the opto. An external power supply provides the
current through the transistor. A the receiving end, the pair goes
through the LED in a second opto. The collector transistor in the
second opto is tied to a resistor that's pulled up to +9 to +12V, and
the emitter is tied to -12V (usually you get the +12 and -12V by
diodes from the DTR, DSR, etc lines). The collector:resistor
junction goes to the RxD pin on the Rs232 interface.
Done right, there's NO galvanic connection between the cable and the
equipment on either end, except at the power supply that provides the
"loop current".
Jim, W6RMK
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