How to build a serial cable for Celestron NexStar telescopes.

The serial connector

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[-] We need a female Sub-D 9pin serial connector. This piece will fit inside your computer's serial port and/or usb adapter.

A female Sub-D 9pin connector

[-] To be sure our cable will work smoothly with any program, we should short some pins on the serial port to create "fake" handshake signals. Otherwise, we could have problems to talk with a "three pin only" serial device. In the following schematics we can see the serial port pinout: we're going to short together RTS/CTS (pins 7 and 8) and DTR/DSR (pins 4 and 6). We will then connect the cable in the following way: wire A to pin 3 (TX); wire C to pin 5 (GND); and wire D to pin 2 (RX).

Schematics of the serial port

[-] This is the back of the serial connector with two little wires we will use to make the shorts:

Serial connector with wires

[-] Once the wires have been soldered the connector will look like this:

Serial connector with shorted pins

[-] We proceed to solder the wires to the connector:

The three wires have been soldered to the serial connector

[-] We can finally close the Sub-D box. Note the metallic "stop" at the bottom of the box that prevents the wires to be pulled too much.

Closing the serial box

[-] The cable is finished!

The finished cable

Copyright (C) 2003 Alessio Sangalli,

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