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David Griffith · April 16th 10, 01:10 PM posted to rec.radio.amateur.moderated

wrote:
David Griffith wrote:
That's one of the first places I looked and where I got the idea.
However, what he did was have a circuit watch the keyboard LEDs. What
I'm trying to do is make something that attaches to an RS232 port. That
way, I can run a three or four wire cable from a server in a back room
to wherever I decide to put my sounder. There are two ways I could do
this. The first is cheap and dirty. It works by energizing the sounder
coils whenever RTS is asserted. That would require special program --
not too tough, but won't be as flexible as in the second approach. The
other is to buffer RS232 in a microcontroller, convert to morse code,
then tap out the message. In effect, this creates a one-way
serial-to-telegraph modem. That second approach is what has me most
interested. Suppose you have a server writing logs to a serial port...
See the sort of bizzare fun that can be had?

Absolutely!

I would think something like this would be fairly easily done in an
Arduino or basicStamp.

The hardware would be near trivial -- get the thing some power, provide
a RS-232 driver, and a open-collector transistor to drive the sounder.
(what kind of voltage/current does a sounder want?)

You'd have plenty of spare output lines (since you only need one to
drive the sounder!) so you could generate a keyed tone on another
output for driving a speaker, useful once you find out why they
dropped sounders like a hot rock once someone invented the BFO(grin)!

I suppose the next thing to do is look for a good simulator that runs on
Linux.

The power requirements of sounders depend on the ohm ratings of the
coils, which is usually stamped somewhere on the sounder. The lower the
ohms, the lower the voltage requirements. Some modern things need to be
done like adding more resistance so it won't be too sluggish. Also a
pair of zeners back-to-back is recommended to prevent something (I
forget what).

Another thing I'll need to use a few lines for would be some means of
varying the output speed. Yes, an alternate output could ride along for
free. Perhaps also a relay to go to the key input of a radio.

--
David Griffith
--- Put my last name where it belongs