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:
In the diagrams below the colors indicate which pins connect to each other.
|Description ||LX200 ||DIN-8 ||DB-9 ||DB-25 ||Name
|+12v DC ||1 || || || ||
|Misc Serial Out ||2 || || || ||
|PC Transmit Data ||3 ||3 ||3 ||2 ||TxD
|Ground ||4 ||4 ||5 ||7 ||Gnd
|PC Receive Data ||5 ||5 ||2 ||3 ||RxD
|Misc Serial In ||6 || || || ||
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.
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 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.
The various RS232 pins go by a confusing variety of names. Fortunately for this purpose,
we need only be concerned with three of them:
Ground, RxD (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
- 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
- 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
Michael 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