Re: Using ONE serial port for shutter AND telescope control ?

Howard Hedlund

Hi Joe,

Here's the RS232 pinout that we have in technical support:

Hope it helps.

Mag. 7 skies!

Howard Hedlund

Astro-Physics, Inc.



From: [] On Behalf
Of Joseph Zeglinski
Sent: Sunday, July 01, 2007 9:37 PM
Subject: [ap-gto] Using ONE serial port for shutter AND telescope
control ?


I posted this idea on the DSLRFocus group, and wanted to ask here, if
there would be any "serial port signal conflicts" on my AP900 GTOCP3

I have a working LED version DSLR shutter release cable, and it seems a
waste to use the one laptop serial port, just to toggle the RTS signal
line to
fire a shutter. Then use a second serial port, wasting a USB port plus a

USB/Serial dongle, to drive the mount either via the Auto Guider port,
or one
of the two serial external control ports. On top of that, there is the
for two serial cables, all the way back to the laptop, to perform the
services of firing a shutter and remotely operating the mount.

Since the shutter release RTS signal isn't required by the AP900, then
there should be no conflict with driving both sets of signals, in one
to two devices. The camera end never sees all the other signals, and
"hopefully", the GTOCP3 is only wired to the Transmit/Receive and common

ground pins (so RTS toggling should not affect it's normal operation,
with a
planetarium program).

If this would work, for astro photography:
1.. You would need just one serial cable to the mount - the nearby
release two wire cable, would be just about a couple of feet long, at
plugged into the LED firing circuit inside the DB9 clam shell, at the

2.. This would save wasting a second computer serial port, or a USB port

along with a USB/Serial dongle.

3.. One less cable to trip over, tangle around the mount, or need to be
packed up every time.
The AP900 user manual (Appendix: B pg. 86) states: "the serial ports do
use X-On/X-Off, or hardware flow control" - (RTS/CTS) - which in this
would be an advantage. I couldn't find any AP900 wiring diagrams for the

GTOCP3 serial ports, to show potential conflicts.

Can anyone verify that the GTOCP3 serial ports are wired for "just" the
signal wires - so they would be blind to the presence of an RTS shutter
release signal?

The only possible problem with this approach might still be that the
serial port drivers won't share a common port, with two programs.

Any feedback would be most welcome.


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