Meade LX200 RS232 Port Connections

To connect an LX200 to a computer you need a special cable. You can sometims buy one from the company that makes the software you’re using but it’s much cheaper to make one for yourself. The parts only cost a few dollars and it will take only a few minutes. All you need is a soldering iron, the appropriate connectors and the information below. It’s really a lot simpler that it looks.


For those of you who know what you’re doing all you need to know is the pinouts:

+12v DC1    
Misc Serial Out2    
PC Transmit Data3332TxD
PC Receive Data5523RxD
Misc Serial In6    

In the diagrams below the colors indicate which pins connect to each other.

LX200 RS232 Port

At right is a diagram of the LX200’s RS-232 port as you see it looking into the panel. Note the odd pin numbering: 1-4-2-5-3-6, read left to right looking into the port (This numbering is taken from the LX200 User’s Manual, don’t expect to see it elsewhere.)

At left is the corresponding 6-pin modular plug (RJ11) viewed from the flat side (top as it is inserted into the LX200; not the end); the connecting pins are on top, the tab on the bottom of the diagram represents the wire.

Mac Ports

The Macintosh’s modem and printer ports use a DIN-8 jack as shown at right looking into the Mac. The diagram at left shows the pins from the end of the male plug. Of course, it’s a mirror image of the diagram of the port. The pins are usually labeled in tiny raised letters.

Making a Simple Cable

Making a cable is just a matter of wiring up the connectors with matching colors as shown below. Connect pin 3 to pin 3, pin 4 to pin 4, and pin 5 to pin 5. (The exact correspondence of numbers is purely accidental.)

(Crossing lines do not connect)

Making a Dual Cable

Though they are labeled as “Unused” in the LX200 manual pins 2 and 6 are actually an extra RS232 port (pin 4 is a common ground). Thus you can make two simultaneous RS232 connections to your scope. This is useful if, for example, you want to connect to a computer and your CCD camera at the same time.

Connect one connector as above. For the other one, connect pin 6 to pin 3, pin 2 to pin 5, and the common ground pin 4 to pin 4.

(Crossing lines connect only where a dot is shown)

Other Computers

Other computers use a variety of different connectors. Most common are DB-25 (right, top) and DB-9 (bottom); they are shown here looking at the pins from the end of the male connector. Connect as for the Mac substituting per the pin-out table above.

Pin Nomenclature

The various RS232 pins go by a confusing variety of names. Fortunately for this purpose, we need only be concerned with three of them: GroundRxD (receive data), and TxD (transmit data).

The diagram at right shows how to connect a DIN-8 (top) to a DB-25 (below).

Richard Mathews says, “On the DIN-8, pins 5 and 8 are both Receive Data (actually RxD- and RxD+). The voltage difference between them is what matters. … To reduce noise, you should connect pin 8 to ground by tying it to pin 4. Note that your diagram for connecting a DIN-8 to a DB-25 already shows this connection, but you don’t show it in the info on connecting the RJ-11 to the DIN-8.” Richard is probably right but my cable works fine anyway.


Modern computers have USB instead of serial ports. To use an LX200 with a USB computer you need a cable such as above plus a serial-USB adapter. I use a Keyspan USB Twin Serial Adapter; there are several other similar products available.


Check your cable carefully before using it. A miswired cable could fry the RS232 ports on either end.

I have made a cable using this information. I have tried to make it correct. But I’m only human. If you burn up your LX200 it’s not my fault.


  • The cable can be very long (100ft or more) if you want. Use heavier gauge wire for longer lengths.
  • It can be somewhat difficult to solder wires to the tiny pins on the backs of these connectors. The easy way to make an LX200-computer cable is to buy a cable with an 6-pin modular plug on one end and another cable with the proper connector (DB-9 or whathever) on one end. Then cut both wires in the middle and just solder the wires together. You may have to use a meter to verify which wire is which.
  • If you want to avoid splicing wire, special tools for working with modular plugs are available
  • You can actually use a 4-pin modular connector if you can’t find a 6-pin one. It will connect to the middle 4 pins of the jack. (But, of course, this won’t work for the dual cable.)
  • Though the LX200’s port uses the same connector as your modem it will not work with a modem. Do not use a simple phone cord to connect your LX200 to a modem or to a phone line.
  • Pin 1 of the LX200’s port is a 12vDC source. But don’t expect it to deliver much current.
  • The LX200’s CCD port is just for moving the scope; it just runs the motors. Some CCD cameras can also use an RS232 port for fuller control of the LX200.
  • You can buy all the parts and tools you need from any electronics supply outlet such as DigiKey or Newark.
  • For info on LX200 cables see Information about Plugs and Cables by R. A. Greiner.
  • Constructing an RS232 cable for a Magellan I by Alistair Symon (Alistair believes this will also work for a Magellan II)
  • How to control the LX-200 from a handheld PC by Matt Considine
  • Robert B. Denny’s nifty Astronomer’s Control Panel for the Meade LX-200 Telescopes
  • Infogenie plugin for Starry Night
  • If all this is too much hassle, you can buy ready-to-use cables from Charles Turner


This page was made possible by the generous contributions of Don DillingerMichael Hart and others on the MAPUG mailing list (plus a little help from the LX200 manual, appendix F). I am grateful for their help but any mistakes are mine.

Bill Arnett; last updated: 2002 Feb 28