Divinehunter

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.

1. Computer Com Port Pinout
2. Db9 Serial Port Pinout
3. Pc Serial Pinout

Pin-outs

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

Jun 23, 2020 The background of the 9 pin serial port First introduced in the 60s, RS-232 is a protocol that defines how the data is transferred, bit by bit from a Data Terminal Equipment (DTE) such as a computer terminal, to Data Communication Equipment (DCE) such as a modem. RS-232 is the common standard used in serial ports.

• This adapter will enable you to connect a HP48 Calculator at the ) 9 pin computer serial port. 9 PIN D-SUB FEMALE to the Computer. +-+ O O O O -/ 4 3 2 1. 4 PIN HP48 to HP Serial Port. 9-Pin HP48; Carrier Detect: 1: Receive Data: 2: 2.
• However, presence of a 9-pin D- subminiature connector is neither necessary nor sufficient to indicate use of a serial port, since this connector was also used for video, joysticks, and other purposes. Serial or COM Pinout Serial or COM Pinout ©Easy PC Online Return to Contents Page 27 28.
• Below is the RS232 connector pinout for testing computer serial port. Data and handshake lines connected. In this case, the sent data is immediately returned back and analyzed by the standard serial port verification software.

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: 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.

USB

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.

Disclaimer

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.

Notes

• 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

Credits

This page was made possible by the generous contributions of Don Dillinger, 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

RS232 serial cable layout

Almost nothing in computer interfacing is more confusing than selecting the right RS232 serial cable. These pages are intended to provide information about the most common serial RS232 cables in normal computer use, or in more common language “How do I connect devices and computers using RS232?”

RS232 serial connector pin assignment

The RS232 connector was originally developed to use 25 pins. In this DB25 connector pinout provisions were made for a secondary serial RS232 communication channel. In practice, only one serial communication channel with accompanying handshaking is present. Only very few computers have been manufactured where both serial RS232 channels are implemented. Examples of this are the Sun SparcStation 10 and 20 models and the Dec Alpha Multia. Also on a number of Telebit modem models the secondary channel is present. It can be used to query the modem status while the modem is on-line and busy communicating. On personal computers, the smaller DB9 version is more commonly used today. The diagrams show the signals common to both connector types in black. The defined pins only present on the larger connector are shown in red. Note, that the protective ground is assigned to a pin at the large connector where the connector outside is used for that purpose with the DB9 connector version.

The pinout is also shown for the DEC modified modular jack. This type of connector has been used on systems built by Digital Equipment Corporation; in the early days one of the leaders in the mainframe world. Although this serial interface is differential (the receive and transmit have their own floating ground level which is not the case with regular RS232) it is possible to connect RS232 compatible devices with this interface because the voltage levels of the bit streams are in the same range. Where the definition of RS232 focused on the connection of DTE, data terminal equipment (computers, printers, etc.) with DCE, data communication equipment (modems), MMJ was primarily defined for the connection of two DTE’s directly.

RS232 DB25 to DB9 converter

Computer Com Port Pinout

The original pinout for RS232 was developed for a 25 pins sub D connector. Since the introduction of the smaller serial port on the IBM-AT, 9 pins RS232 connectors are commonly used. In mixed applications, a 9 to 25 pins converter can be used to connect connectors of different sizes. As most of the computers are equipped with the DB9 serial port version, all wiring examples on this website will use that connector as a default. If you want to use the example with a DB25, simply replace the pin numbers of the connector according to the conversion table below.

RS232 serial loop-back test plugs

The following RS232 connectors can be used to test a serial port on your computer. The data and handshake lines have been linked. In this way all data will be sent back immediately. The PC controls its own handshaking. The first test plug can be used to check the function of the RS232 serial port with standard terminal software. The second version can be used to test the full functionality of the RS232 serial port with Norton Diagnostics or CheckIt.

Testing occurs in a few steps. Data is sent on the Tx line and the received information on the Rx input is then compared with the original data.

The signal level on the DTR and RTS lines is also controlled by the test software and the attached inputs are read back in the software to see if these signal levels are properly returned. The second RS232 test plug has the advantage that the ring-indicator RI input line can also be tested. This input is used by modems to signal an incoming call to the attached computer.

RS232 null modem cables

The easiest way to connect two PC’s is using an RS232 null modem cable. The only problem is the large variety of RS232 null modem cables available. For simple connections, a three line RS232 cable connecting the signal ground and receive and transmit lines is sufficient. Depending of the software used, some sort of handshaking may however be necessary. Use the RS232 null modem selection table to find the right null modem cable for each purpose. For a Windows 95/98/ME Direct Cable Connection, the RS232 null modem cable with loop back handshaking is a good choice.

RS232 null modem cables with handshaking can be defined in numerous ways, with loop-back handshaking to each PC, or complete handshaking between the two systems. The most common null modem cable types are shown here.

Db9 Serial Port Pinout

Pc Serial Pinout