This page outlines how I made a working DB9 RS-232 serial communications cable for my Meade DS-115 telescope.
This interface allows the telescope to connect to my computer through the telescope’s Autostar input socket. It is then possible to use various graphical astronomy packages on the computer to move the telescope’s motors and view night sky objects automatically, by simply clicking on the computer screen. The communications cable also allows for communication and transfer of data between the Meade Autostar handset for database update and firmware control (use Autostar firmware updates with caution!).
Why figure out the wiring rather just than buy the cable? Because that is the DIY way, since this is “just a cable” (… and the fact that the proprietary cable is hideously expensive for “just a cable”!).
If you don’t mind dishing out cash and buying a cable instead, you can check out the Meade cable for the pre-EXA model telescopes here from E-bay or Amazon. (Note: this cable is for an older styled Meade telescope and may not be compatible with newer models. Be sure to double check what cable your specific telescope model requires.)
Making and using this RS-232 serial interface cable has been simple as well as extremely satisfying. I have not tested this cable with other similarly aged models of Meade telescope, but I would cautiously assume other telescopes may also be compatible (Meade D-114, etc). Especially if they have a similar looking Meade cable junction box arrangement. It is very likely the company used the same electronics and cable wiring for each the various scope models of the time. After saying that, I provide this information with all hopes it will assist others, but without any guarantees that wiring will be compatible, or will not damage, your particular telescope (if a differing model to the DS-115).
Whether buying the real cable, or making this DIY communications cable yourself, allowing computer aided mapping and navigation of the telescope motors will be a major upgrade to your telescope and astronomy experience if you have not tried it before. Computer object locating software really opens up the usually hidden depths of space to everyone and takes the hassle out of deciding what to find and look in the night sky.
The Telescope and Autostar Handset
Before we go further, let’s look at the details of the Meade telescope, handset and other equipment we are dealing with.
The Meade DS-115 is an older style 115mm reflector telescope with a focal length of 910mm (f/7.9). This particular model appears to me a somewhat obscure and uncommon model, but seems similar in most respects to the relatively common Meade DS-114.
My telescope came supplied with both a simple handheld push-button motor controller board, as well as the (then) optional upgraded Meade Autostar 495 Handset (pictured in fig 2). The Autostar handset provides full setup and tracking control for the Meade series telescopes. The handset also contains a database of commonly observed night sky objects so positioning coordinates and tracking can be automated using the handset alone. While the handset does provide limited visual reference through a two line LED display, it does not compare to the rich graphical experience of using a full virtual sky map on a computer screen for telescope positioning.
The telescope has a power and cable socket junction box at the head of the tripod. The (female) socket holes are labeled “HEX”, “AZ”, “ALT” and “AUX”. These correspond to the positions for attachment of the controller handset (or Autostar handset), the azimuth motor, the altitude motor control and an auxiliary attachment for use of a focus motor if desired, respectively.
The separate Meade Autostar handset has two sockets on its base. The eight point contact socket is for connection of the Autostar handset directly to the telescope’s “HEX” socket (described above).
The additional four contact point socket is for serial port interfaces with a computer. Hence, this is the socket we need to connect through with our DIY connection cable in order to use our chosen astronomy software package to drive the telescope motors. Please note that the AUX (auxillary) port, or any other port on the telescope itself, are not used for computer interfacing purposes. All serial communications with a computer need to be done through the Meade Autostar interface socket!
What is a DB9 RS-232 serial communications cable?
DB9 refers to the standard design cable connector end that terminates in 9 contact pins. It is also called a DE9 connector. (Do not confuse this with the similarly sized and shaped 14 pin video plug that was common for connecting video screens some years ago.) You will need one of these DB9 connection plugs for this project, either from an old cable (easiest), or as a new part.
RS-232 refers to the RS-232 communication protocol that was commonly used for cable data transfer in the past. Even today, it is still a handy protocol for communicating with serial and printer ports of older computers and cards. The Meade DS-115 telescope uses this protocol for all data transfer.
Whether interested in the technical jargon or not, don’t get turned off by it if you have not run into these terms before. They are not important for anyone who just wants to make the cable itself and get things working.
1 x DB 9 connector plug (also named DE-9 connector)
- A DB25 (ie: 25 pin plug) can also be used if you intend to drave the telescope from a computer printer port rather than the 9 pinned RS-232 serial port. Pinout connections will obviously differ slightly if using the DB25, but the correct pins can be found by using a DB9 vs DB25 cross reference chart. Sorry, I haven’t gotten around to checking the specific pins required for the DB25 myself.)
1 x 4 pin network socket plug (or standard 6 pin telephone plug can also be used)
1 x length of network cable, 1m to 50m long depending on your telescope use preferences.
Making the Cable Connections
The Meade communications cable has a DB9 connector plug on one end and a narrowed 4 connector telephone like socket on the other.
To make the connection cable, I therefore cut and combined an old 4 wire telephone cable (with plastic male socket fitted), a 20m network cable, and a female DB9 adapter end. The network cable was cut to length and 3 wires were soldered to the DB9 plug pins to match the arrangement shown in figure 4.
I then cut the telephone cable and kept the desired plastic plug on the end. (I took this approach rather than using new cable and separate plastic socket as I had the unused cable laying around. Further, it is usually easier stripping and soldering mid-cable wires together than it is to mess with plastic connector clamping. While soldering signal wire is not usually “technically correct” due to potential interference and shielding problems, we can easily get away with it for this low baud rate, non-critical application.
Once the three correct telephone wires were stripped and ready to connect, they were soldered onto the network cable in a way that matches the arrangement shown in figure 4. The telescope interface socket for fitting of the plastic clip adapter is narrower than the standard telephone connector. A standard telephone connector will therefore require a small amount of filing or grinding on both sides of the plastic clip plug to allow it to fit snugly (unless you initially manage to find the relatively uncommon narrow adapter). It is not a big deal to grind the telephone adapter as the plastic shaves away easily. File away evenly on both side until the connector fits snugly in the Meade Autostar’s bottom interface socket.
The telescope communications cable was made long for convenience sakes. This was so I can drive the telescope from inside (in the warmth), while the telescope sits outside. As long as you are using network cable or similar, anything up to at least 50m length should be usable for RS-232 communications. If you start running into signalling, connection and dropout problems however, make the cable shorter.
Basically, the wire connection is a simple null-modem arrangement involving only the transmit data (TD), receive data (RD) and signal ground (SG) pins of each side of the interface.
With all wiring checked, you are good to go!
Good luck. We wish you clear skies and out of this world experiences in your astronomy!