Instruction manual

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Appendix 4 Serial Ports and Cables
Introduction
In the following discussion, we use DEVICE to stand for either Digital Dome Works, Dome Wizard, RoboFocus or
other device as may be appropriate to your installation.
The communication between the computer and the DEVICE is via a "serial" cable connected to a PC serial port,
called a COMmunications Port (for purposes of this discussion RS232 and “serial” refer to the same thing). If the
settings for the software do not match the port, communication will not succeed. In this section, we'll talk about
COM ports.
A standard PC running a recent version of Windows (or alternative operating system) frequently has three serial
ports numbered COM1-COM3, which are often assigned to:
• mouse (usually COM1)
• spare(COM2)
• modem (usually on COM3 in our port assignments)
Some PCs have a separate special input for the Mouse (PS/2 style), which frees the COM1 port for other uses.
A remote control observatory may require that the control computer have enough serial ports to serve:
• mouse
• modem (optional)
• telescope
• CCD (may be a parallel port rather than serial)
• DEVICE
Task: You will need to assure that your computer has the correct number of RS232 ports to serve your needs, and
you will need to have the proper cables to run from your computer to the observatory. In this appendix, we will
discuss both issues.
Serial Cable Options
Regardless of how many conductors the long cable has, we only use three for the serial communication (e.g., black,
green, and yellow on 6-conductor cable).
We provide nominal 10-ft. signal cables to connect your PC to DEVICE. This will work fine if your computer is in
or next to the dome. However, if you need to run longer cables, you can order them from us or easily build and
install your own. For relatively short runs (roughly up to 50-75 feet), you can use standard six-conductor flat
telephone cable with standard six conductor connectors.
If you are at a substantial distance, say, 100 ft or more. You may need to run the cable in some type of conduit
underground, and you may want cable that is physically stronger. The cable for the RS232 can be almost any
reasonably low capacitance, three (or more) conductor cable, for example, twisted shielded pair. For long runs, use
reasonably large wire (e.g., 20 gauge conductors). We have used a variety of wire types, including “thermostat”
wire (4 conductor) and even Romex #14 building wire (2 wires plus ground).
The easiest and most flexible way to make the connections is to use a standard 6-conductor telephone jack (female)
with wire leads. You can then simply hook the proper wire color to each of your long wire conductors, and then use
our standard (or your own) phone cables for inside the dome and control room. The colors we use are Black
(ground, DB9-5), Yellow (PC in DB9-3), and Green (PC out DB9-2). You can also use various other types of
connectors (e.g. DB9, use numbers above plus jumper DB9-7 and 8). See the schematic of connectors in the rear of
this instruction manual for further details.