Connecting a Telescope

Connecting a Telescope to Your Computer:

Connecting is Simple!

Most telescopes that ScopeDriver supports communicate at a very slow speed (9600 bps), and so connection issues are uncommon. All you need is a serial port on your computer (or a serial port adapter if your computer has no serial ports), a cable, and the telescope.

Your
Computer

USB-to-Serial Adapter
(if needed)

Serial Cable

Your
Telescope

Step One: The Serial Port

Many computers have a built-in serial port. On PC’s, the ports are usually named COM1 and COM2. On older Macintosh computers, the ports are named Modem and Printer. If your computer has a free serial port, you just need to buy or build a cable that fits your computer’s serial connector.

PC serial ports will either have a “DB-25” connector (a two-row connector with 25 pins) or a DB-9 pin connector. Macintosh serial ports employ a “DIN-8” connector with eight contacts.


DB-9 (PC)	DB-25 (PC)	DIN-8 (Macintosh)

Many newer computers do not have serial ports. Fortunately, many companies produce USB-to-serial adapters that simply plug into your computer’s USB port. If you need a USB-to-serial adapter, make sure you get one that is designed for standard serial devices. Do not purchase a so-called “PDA adapter”; they may be cheaper, but are unlikely to work with your telescope.

If you do need to install an adapter, make sure you also install the latest driver software from the manufacturer’s web site. Restart your computer after installing the driver software.

Many manufacturers produce excellent serial adapters. We have had excellent experiences with the Keyspan adapters and their support software.

Your computer’s built-in serial ports and/or your adapter’s serial ports should appear in the Connect window’s Port: pop-up menu. If your adapter’s ports don’t appear there, either the adapter’s software is improperly installed, the adapter itself is improperly installed, or the port may be in use by other software (such as fax software).

Step Two: The Telescope

The serial port on your telescope is usually labeled “RS-232” (a serial interface standard, where “RS” stands for Recommended Standard). The location of the port, as well as the type of connector, varies between models, as described below:

LX200 (both “Classic” and “GPS”): The telescope’s serial port is on the telescope base. It is labeled “RS-232,” and is a six-conductor RJ-11 jack.
Meade Autostar #495 and #497: The telescope’s serial port is on the hand controller. It is labeled “RS-232,” and is a four-conductor RJ-22 jack.
Meade Autostar #494 and Starfinder: The serial port is on the telescope’s base, and a special cable containing active circuitry (the Meade 506 Cable) must be used. Note that these models do not support many ScopeDriver commands.
Losmandy Gemini: The serial port is on the electronics box, labeled “RS-232,” and is a four-conductor jack.

Step Three: The Cable

The remaining piece of required hardware is the cable that connects your computer’s (or serial adapter’s) serial port to your telescope’s serial port. You can either construct your own cable, or purchase one ready-made.

When building or selecting a cable, you need to make sure that one end fits your computer’s (or adapter’s) serial port, and that the other end mates properly with your telescope’s serial port.

For those wishing to purchase a cable, Charles Turner offers ready-made cables for LX200’s, Autostars, and Geminis. He is familiar with many types of serial adapters and telescopes, and so can advise you on the correct cable needed for your setup. Losmandy also sells PC-to-Gemini cables.

If you’re handy with a soldering iron, you may wish to construct the necessary cable yourself. The below links may be helpful:

Bill Arnett discusses building a cable to connect a Mac or PC to an LX200.
Stephen Voss covers building a cable to connect a Mac or PC to a Gemini.
R.A. “Doc” Greiner has a page with LX200 cable specifications and information.
Mike Weasner links to a great deal of Autostar cable information.

Once you have your serial adapter (if required) and your cable, you’re ready to connect everything up.

Step Four: Connecting

It’s best to start by connecting everything indoors. If problems develop, you won’t lose observing time, and things will be easier to troubleshoot with good lighting.

Begin with the power removed from your telescope and your computer. While some people report success with “hot-plugging” serial connectors, it is possible to damage your telescope’s serial interface circuit if you connect with the power on to either your computer and/or telescope.
Next, connect your cable between your computer’s (or your adapter’s) serial port and your telescope’s serial port. Switch on the telescope, then start up your computer.
Launch ScopeDriver. When the Connect window appears, look for the name of your serial port in the Port: pop-up menu. If it’s not there, check the Troubleshooting section at the end of this document.
Next, select your telescope model from the Telescope: pop-up menu.
Click the Connect window’s Connect button to initiate a connection.

Check the below section if you encounter any error messages while connecting or while using ScopeDriver.

Troubleshooting

Occasionally, something may go wrong which causes an unreliable or failed connection. Such problems are usually easy to diagnose and solve.

ScopeDriver doesn’t list my built-in serial port in the Connect window’s Port: pop-up menu.

This could mean that some other application program is using your computer’s serial port. Try disabling any fax, communications, or other software that communicates via the serial port, then restart the computer and try again.
Try booting in safe mode. On the PC, this is usually done by holding down the F8 key during a restart, although this may vary by version. On a Macintosh, hold down the SHIFT key as you restart the machine, until you see the message “Safe Boot” or “Extensions Off.” After startup completes, try connecting again.

ScopeDriver doesn’t list my USB-to-serial adapter’s serial port in the Connect window’s Port: pop-up menu.

Make sure the adapter is properly connected to a working USB port.
Ensure that the adapter’s driver software is installed and up-to-date. Download the latest driver software from your adapter manufacturer’s web site, install the software, restart your computer, and try again.
Make sure that you are using an adapter designed for general serial devices. Specialized “PDA adapters” may be inexpensive, but they often are incompatible with non-PDA devices.
Some other application program may be using your adapter’s serial port. Try disabling any fax, communications, or other software that communicates via the serial port, then restart the computer and try again.

My serial port appears in the Connect window’s Port: pop-up menu, but I receive an error when I try to connect or after connecting.

First, make sure the correct model is selected in the Connect window’s Telescope: pop-up menu. Also click to de-select the Increase Responsiveness control, then try connecting again.
Try selecting a different serial port from the Port: pop-up menu in the Connect window.
Make sure your telescope is powered up, and complete the telescope’s polar alignment procedure, then try again. Some telescopes refuse to accept serial commands until the telescope is aligned via a one- or two-star alignment.
Check to make sure that all connectors are firmly seated in their sockets.
Long cable runs can lead to “noise” on the serial line. If you’re using an extension cable, try removing it before connecting again. Also beware of unshielded wire connections, which may be insulated but do not keep interference out.
If you are using a serial adapter, make certain that you are using its latest drivers. Outdated drivers may lead to unexpected behavior or even system freezes.
Power everything down, then check your serial cable with a continuity tester or ohmmeter. The cable links provided earlier in this document can guide you through the procedure.
Ensure that you’re using the correct cable. Cables that look identical may sometimes have very different characteristics.
Make sure that you are using an adapter designed for general serial devices. Specialized “PDA adapters” may be inexpensive, but they often are incompatible with non-PDA devices.
Some other application program may be using the serial port. Try disabling any fax, communications, or other software that accesses the serial port, then restart the computer and try again.
Check to see if updated firmware is available for your telescope. Sometimes, a “bug” in the firmware may lead to unexpected behavior.
Check ScopeDriver’s Communications window to see if any commands are reaching your telescope. In the Connect window, right-click (Mac: CONTROL-click) in a blank area of the window and select “Show Communications Window” from the contextual menu. This causes the Communications window to appear, where you can see ScopeDriver’s commands being sent to your telescope, and the instrument’s replies, if any. Click the Connect window’s Connect button to try connecting again.

My computer locks up when I try to connect.

This symptom is almost exclusive to USB-to-serial adapters. It indicates that either the driver software is incompatible with your system, or that the adapter itself is incompatible. Try installing the latest version of your adapter’s driver software from the manufacturer’s web site. Note that extremely low cost serial adapters — and most “PDA adapters” — are likely to cause problems.

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Page updated Monday, August 4, 2008 9:01 PM