The Shoestring Astronomy Store

Guide Port Interface Products


Shoestring Astronomy has always been an "evening and weekend" enterprise when I was employed full-time. Now that I am retired, we do like to travel frequently. I will do my best to fill orders and respond to emails in a timely manner, but please realize that there may be times when I cannot respond as quickly as I would like to.

Thanks for your patience, and your patronage. Doug Anderson

Thanks to webcam technology, it is now easy and much less expensive to set up your own autoguiding system. You'll need a PC or laptop computer, a webcam or other video device, autoguiding software, and some sort of interface so that the computer can talk to your telescope mount and direct it's motion. Of course, you will also need a telescope mount that is capable of receiving tracking correction commands. To use our products shown below, your mount will need an ST-4 compatible guide port. More information on ST-4 guide ports can be found in our Guide Port Cabling document. If you are new to webcam autoguiding, click here for a brief overview of the key elements of any webcam autoguiding system.

The GPUSB guide port interface adapter plugs directly into a USB port on your computer or a USB hub attached to your computer. Using an RJ-12 cable, the adapter connects to the guide port of your telescope mount. This guide port interface uses optocouplers to electrically isolate the computer from the telescope, eliminating a possible source of electrical interference. This interface adapter requires no external power source since it receives its power via the USB cable. More information can be found by clicking here to view the User Manual.


We had one case where a customer used an improperly wired cable with his Celestron Advanced Series Goto mount. This resulted in damage to the electronics in his mount, as well as damage to the interface adapter. We can't stress enough the importance of using a properly wired cable. If you choose to make or buy your own from another source, please be sure it is built per the description shown in this document.

We also offer cables and other accessories that are known to work with the GPUSB, taking more of the guesswork and locating parts off your hands.


You will need third-party software that supports these products as part of your autoguiding system. The matrix below shows the software packages we are aware of. If you know of others, please email us and let us know. Shoestring Astronomy is continuously working with software vendors to add support for our products. If your favorite software is not compatible, ask them to add us! For software packages that use ASCOM to interface to the GPUSB, you will first need to download and install the ASCOM platform from, then download and install our GPUSB ASCOM driver, see download details below.
Supports GPUSB



Astro IIDC (Macintosh)


AstroGuider (OS X)


Autostar/Envisage by using Guidestar LX200 Software Emulator








KStars (Linux)




MaxIm DL


MaxIm Essentials




PHDGuiding (Windows)

Yes (Directly or ASCOM)

PHDGuiding (Macintosh)


wxAstroCapture (Windows and Linux)



Any mount with an ST-4 compatible autoguider port should work with these adapters. Mounts that we are aware of include the Losmandy GM-8 and G-11 (see note below), Takahashi EM-10 (must use the GPCNV-TAK guide port converter), Meade LX-200 (see note below), Meade LX-90, Celestron Nexstar i-series, Celestron Celestar 8, Celestron Advanced Series GoTo, Celestron CGE series, Celestron CPC series, Orion Atlas EQ-G style, Gemini G-41, Skywatcher HEQ5-Pro, Astro-Physics AP900 QMD, JMI NGT, Vixen SkySensor2000 (must use the GPCNV-SS2K guide port converter), and Tom O. Equatorial Platform. Even if your mount does not have autoguide port, it may be possible to modify your handcontroller to add an ST-4 compatible autoguide port (see below).
NOTE to Losmandy Owners: If you have a GM-8 or G-11 without the Gemini box, you will need the GPUSB. If you are using the NEW style Gemini box (the NEW style has a circular DIN connector to connect to the motors), then you will need the GPUSB. If you are using the OLD style Gemini box (the OLD style has a modular RJ-45 connector to connect to the motors), then you will need the GPUSB-AH.
NOTE to Meade LX-200 Owners: The diagram shown in the manual for the older "classic" Meade LX-200 makes it appear that the CCD port does not follow the ST-4 standard. The CCD port is indeed ST-4 compatible, but Meade chose to use a nonconventional pin numbering scheme, and did not provide a diagram that shows how the pins are physically numbered.
NOTE to Kenko Skymemo Owners: The Kenko Skymemo does allow for autoguiding, but only along the RA axis. You will need our GPUSB-AH guide port interface, and the GPCBL-SKY adapter cable.


Many mounts that have motorized movement in RA and Dec, and that have handcontrollers to manually guide the mount, can be modified to add an ST-4 compatible guide port. The best example of this is older EQ style mounts. Using the GPKIT-EQ kit of parts that we sell below, and the instructions found here, you can modify this handcontroller to work with our GPUSB.
Several customers have modified the Vixen DD-1 handcontroller in a manner similar to that for the EQ handcontrollers. You can use the EQ documentation, our GPKIT-EQ, and this picture to perform this modification. However, because of a difference in the internal electronics, the Vixen DD-1 modification must use our GPUSB-AH guide port interface adapter. The GPUSB will not work.
The Takahashi TG-SE handcontroller can be modified by adding relays as shown in this schematic.
If you don't own one of these mounts, don't give up hope. Almost any handcontroller can be modified by adding relays in parallel with the directional pushbutton switches to add an autoguide port. See our Handcontroller Modification Guidance document for suggested schematics and part numbers.

GPUSBCheck by Shoestring Astronomy
GPUSBCheck is a simple, free software application that you can use to verify that your GPUSB, computer, and scope mount are all working together properly. You can download them using the links found below. You should use this the first time you set up your system. You can also use it as a debugging tool anytime your system is not functioning properly. If your system works fine with GPUSBCheck, but not with your third-party software, then the problem most likely lies with the third-party software and you should contact them for technical support. If your system does not work with GPUSBCheck, then you should contact us for technical support.

Yahoo Autoguiding Group

Cedric Thomas has created a wonderful gathering spot for everyone interested in autoguiding. TheYahoo Autoguiding Group is a place where you can tap into the experience of hundreds of current and future autoguiding amateur astronomers.

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gpusb.jpg (64 kbytes)

USB Guide Port Interface (guide port cable not included)

Click for more information

gpusb.jpg (64 kbytes)

USB Guide Port Interface for OLD Gemini (guide port cable not included)

Click for more information


GPUSB User Manual

Click here to view/download. (Requires Adobe Acrobat Reader)

  Absolutely Free  

Install GPUSBCheck

Click here to install the free software you can use to verify your GPUSB.

  Absolutely Free  

Install GPUSB ASCOM Driver

Click here to install our free GPUSB ASCOM driver.

  Absolutely Free  
gpcnv_tak.jpg (69 kbytes)

Guide Port Converter for Takahashi Mounts

Click for more information

gpext.jpg (67 kbytes)

Guide Port Converter for SkySensor2000

Click for more information


Skymemo Adapter Cable (8 feet)

gpext.jpg (67 kbytes)

Guide Port Extension

Click for more information

gpspl.jpg (76 kbytes)

Guide Port Splitter

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Try L-Com

gpfc_7.jpg (142 kbytes)
Guide Port Flat Cable, 7 feet
gpfc_14.jpg (119 kbytes)
Guide Port Flat Cable, 14 feet
gpfc_14.jpg (119 kbytes)

Guide Port Flat Cable, 25 feet

(Actual cable not shown)

gpcc_5.jpg (139 kbytes)
Guide Port Coiled Cord, 5 feet when extended

(Color may vary)

gpcc_7.jpg (139 kbytes)

Guide Port Coiled Cord, 7 feet when extended

(Actual cable not shown, color may vary)

gpcc_10.jpg (139 kbytes)

Guide Port Coiled Cord, 10 feet when extended

(Actual cable not shown, color may vary)

Discontinued Discontinued
gpcpl.jpg (95 kbytes)

Guide Port Cable Coupler

If the cables above are not long enough, use this to join two together.

gpkit_eq.jpg (71 kbytes)

Guide Port Conversion Kit for EQ-style mounts

Parts needed to add an ST4 compatible guide port to an EQ-style dual axis handcontroller.


Instructions for GPKIT-EQ

Click here to view/download. (Requires Adobe Acrobat Reader)

  Absolutely Free