DIY Autoguider (Part 2: Setting-up the Guiding Software)

Guiding commands from the computer are sent through a port called ‘LPT1‘, or the parallel port (or sometimes called printer port). It is a kind of interface that allows a simple way for a computer to communicate with other devices.  We will try to convert these ‘commands‘ into a form that can be easily interpreted by your telescope mount. The simplest way to do that is to convert the commands into light pulses using Light-Emitting Diodes (or LEDs). These light pulses in turn will be used to drive what is called a ‘light activated switch‘ that we will connect directly to the autoguider port or hand controller. In this DIY guide, we will focus first on how a computer (with the use of the guiding software called GuideMaster) can generate light pulses, by connecting LEDs to the computer’s parallel port.

The parallel port is mounted on a socket called DB25F(F stands for ‘female socket’) or DB25M(M stands for ‘male socket’). It has 25 pins (1 to 13 top row, 14 to 25 bottom row). For this project, we are only interested in pins 4, 5, and 25 (other pins will be utilized however in future upgrades). Shown below is a photo of my laptop’s parallel port.

A female parallel port (DB25F). Note the location of pins 4,5, and 25 (see arrows).

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