UPDATED (February 2016): PAGE UNDER CONSTRUCTION. This page is being updated to reflect the current changes and upgrades in my setup. I am now using other alternatives such as a GPUSB or an Arduino as a means to establish communication between the telescope and the mount since the parallel port (the port used in the original version of this DIY) is now becoming obsolete.

WARNING: I assume no responsibility for any damage caused to your equipment by following the information presented here. Please proceed with caution and follow instructions at you own risk.

I this part, we will setup four things:

  • the guiding software (PHD2) and the appropriate settings
  • the GPUSB driver
  • the web camera’s driver
  • check whether the GPUSB and the guide connects without problem when used together in the guiding software

(Note: I will write a separate article on how to use an Arduino instead of the GPUSB.)

1. The guiding software that we will use is the PHD2 Guiding. Most of the settings are left to their default values, but some values specific to your setup must be entered, and in some cases, experimenting with some other values is recommended to achieve best results.


Click the ‘brain’ icon to access the Advance Settings tab. In the Global tab, enter the focal length of your guidescope.


At the start of a guiding session, PHD2 Guiding attempts to determine how well your mount responds when given a set of instructions to move east and move west (a process called calibration). Adjust the ‘calibration step’ until you find a value that works for your setup. Alternatively, you may use the ‘Calculate’ button for help. The Maximum Duration pertains to the maximum length (in milliseconds) of each guide pulse. It is recommended to conduct some experiment with your setup to find the most appropriate values.


If you are using a modified camera, find a delay value that works with camera.

2. Autoguiding requires a means for a computer to send guiding signals to a telescope’s mount. For most mounts, especially the entry-level ones, a separate device can be used to enable the computer ‘talk’ to the mount—an example of which is a USB Guide Port Interface or GPUSB.

Install the GPUSB ASCOM Driver to allow guiding programs to recognize the GPUSB hardware. Install also the diagnostic tool called GPUSBCheck (to check if the GPSUSB works properly).


Connect the GPUSB to the computer using the USB port and then run GPUSBCheck. Click Connect in the main menu. If the GPUSB works as intended, it should return the message “GPUSB adapter found!” You can then play with the buttons and the GPUSB should respond accordingly.

3. Install the camera’s driver. In this setup, I will be using a Logitech 4000 web camera. It comes with an installation CD which contains all the necessary drivers for the webcam. Drivers for most recent operating systems can be found here.

Logitech 4000 installation disc


4. Test whether the guide camera and the GPUSB work together in PHD2 Guiding.


Click the Camera Icon to access the Equipment tab and then select in the drop-down menu “Long exposure Serial webcam” as the camera and GPUSB as the mount.



Set the guide camera’s settings by clicking the settings icon, and then select the appropriate port where your camera is connected. Other settings are usually left to default values, but you may need to change some of them depending on how your camera was modified.


Click the Connect icon for the Camera and the Mount. PhD2 Guiding will attempt to establish a connection with camera and the mount. You will know that a successful connection is established when the buttons change to “Disconnect” (also a status is displayed on the lower left corner of the PHD2 Guiding window.) Click Close.


Click the loop icon (green) to begin guiding. Adjust the guide camera exposure in the drop-down menu if necessary. To exit, click Stop.

In my next post, I will describe how to connect the GPUSB to a telescope, through the ST-4 port or an improvised DIY port through the hand controller (if the mount has no ST-4 autoguider port).

UPDATED (January 2016): This post has been updated to eliminate the need for a parallel port, which is now becoming obsolete.

Related articles:
DIY Autoguider (Part 1: Introduction)
DIY Autoguider (Part 2: Setting-up the Guiding Software)
DIY Autoguider (Part 3: Wiring Diagrams)
DIY Autoguider (Part 4: Autoguiding and Polar Alignment)

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For DIY astronomy projects useful for astrophotography, click here.

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© Anthony Urbano (Manila, Philippines)