Long distance stamp to stamp communications

Archiver

For my current project I will need to establish serial communications
between two stamps at opposite ends of a 150-200 foot cable (running
off of separate power supplies.) What would be the best way to do
this? Is flow control (in the manner of the SERIN and SEROUT
commands) possible over these distances?

I will also need to use a stamp to switch several high power devices
(most notably a set of automobile headlights, but also a fuel pump
and some others), what kind of current do relay coils draw to hold
them shut? How can I use more than just 1 or 2 relays without
exceeding the stamp's current limits?

Thanks for any help,
Douglas McClean
jxm156@p... or IDiggles@a...

Archiver

If you're concerned about driving more than one or two relays.... you could
always drive a transistor, which in turn drives the relay.... the power to
turn on the transistor will be very slight. Or, I'm on shaky ground, but
perhaps solid state relays already do this...

---

Original Message

---

From: <IDiggles@a...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, January 31, 2001 6:57 PM
Subject: [noparse][[/noparse]basicstamps] Long distance stamp to stamp communications


> For my current project I will need to establish serial communications
> between two stamps at opposite ends of a 150-200 foot cable (running
> off of separate power supplies.) What would be the best way to do
> this? Is flow control (in the manner of the SERIN and SEROUT
> commands) possible over these distances?
>
> I will also need to use a stamp to switch several high power devices
> (most notably a set of automobile headlights, but also a fuel pump
> and some others), what kind of current do relay coils draw to hold
> them shut? How can I use more than just 1 or 2 relays without
> exceeding the stamp's current limits?
>
> Thanks for any help,
> Douglas McClean
> jxm156@p... or IDiggles@a...
>
>
>
>
>

Archiver

I have set up rs-485 networks (ala the app kit) with separations of as much
as 70 feet with no problem using three wires( signal a/signal b/ground) and
a load resistor st the ends.

Archiver

>For my current project I will need to establish serial communications
>between two stamps at opposite ends of a 150-200 foot cable (running
>off of separate power supplies.) What would be the best way to do
>this? Is flow control (in the manner of the SERIN and SEROUT
>commands) possible over these distances?

RS-485 can do this easily. It uses differential signals and twisted pairs
that eliminate the electrical noise that can show up over these distances.

With just 2 Stamps, you can use full duplex (2 wires for each direction)
and the programming will be easier. You can communicate exactly the same as
if you were connecting the stamps directly. Use port pins, not SIN and SOUT.

If you want to use Fpin flow control, you can connect these via RS-485
also, in the same way as if they were data lines.

The Max3081 (www.maxim-ic.com) is an example of a transceiver to use at
each end. It has limited slew rate, which means it's low speed, but plenty
fast for a Stamp, and doesn't need terminating resistors in most cases (so
you save on parts and power consumption).

The cable should also include a ground wire.

I have more about RS-485 here:

http://www.lvr.com/serport.htm

Jan Axelson
http://www.lvr.com
jan@l...

Archiver

Jan,
You say the cable should include a ground wire for this to work
properly. Would a relatively large wire be needed if the two ends are
working off of separate power supplies? (A 12 volt battery at one end
and a marine electrical system (battery, alternator, etc) at the
other) My only concern is that for this application to work I would
ideally like to thread all of these wires through a garden hose, so
space is limited.

Thanks for the help,
Doug McClean

--- In basicstamps@y..., Jan Axelson <jan@l...> wrote:
>
> >For my current project I will need to establish serial
communications
> >between two stamps at opposite ends of a 150-200 foot cable
(running
> >off of separate power supplies.) What would be the best way to do
> >this? Is flow control (in the manner of the SERIN and SEROUT
> >commands) possible over these distances?
>
> RS-485 can do this easily. It uses differential signals and twisted
pairs
> that eliminate the electrical noise that can show up over these
distances.
>
> With just 2 Stamps, you can use full duplex (2 wires for each
direction)
> and the programming will be easier. You can communicate exactly the
same as
> if you were connecting the stamps directly. Use port pins, not SIN
and SOUT.
>
> If you want to use Fpin flow control, you can connect these via RS-
485
> also, in the same way as if they were data lines.
>
> The Max3081 (www.maxim-ic.com) is an example of a transceiver to
use at
> each end. It has limited slew rate, which means it's low speed, but
plenty
> fast for a Stamp, and doesn't need terminating resistors in most
cases (so
> you save on parts and power consumption).
>
> The cable should also include a ground wire.
>
> I have more about RS-485 here:
>
> http://www.lvr.com/serport.htm
>
> Jan Axelson
> http://www.lvr.com
> jan@l...

Archiver

>You say the cable should include a ground wire for this to work
>properly. Would a relatively large wire be needed if the two ends are
>working off of separate power supplies?

RS-485's differential drivers have equal and opposite currents that
normally cancel each other out almost completely. The only current in the
ground wire is the very small current due to any mismatch between the
drivers. So it doesn't have to be large in diameter.

Jan Axelson
http://www.lvr.com
jan@l...