The parallel port is one of the easiest computer ports to interface with. It allows any computer to ‘talk’ with other devices like turning on and off a light bulb, or any other electrical appliance for that matter. Obsolete as it may seem, the parallel port is still used today to perform tasks such as controlling a telescope during autoguiding operation and controlling the precise timing of relays in a dedicated long-exposure camera used in astrophotography.


A computer’s parallel port featuring the pins relevant in controlling various astronomical equipment

Most computers produced nowadays, however, are no longer equipped with parallel ports. For someone who needs access to this port, possibly because his or her system requires this type of port, or simply because one would just want to explore how computers can interact with other devices, there are two possible options:

(1) if a computer has a serial port, one may simply construct a DIY serial-to-parallel port converter (serial port is converted directly to parallel port) or

(2) if the computer has no serial port, but has a USB port, one can first convert the USB port to a serial port, and then convert the serial port to a parallel port using a DIY serial-to-parallel port converter (a USB port is converted first to serial port, then the resulting serial port is then converted to a parallel port).


A DIY serial-to-parallel port adapter will essentially allow a camera or a telescope requiring a parallel port to utilize a computer’s serial port instead. If no serial port is available but a USB port is available, a USB-to-serial port adapter may be used to first convert the USB port into a serial port. Direct conversion from USB port to a parallel port will not work.


The adapter functions as an electronic relay and may be may be constructed using diodes, resistors, and transistors. An optional switch may be included to turn on and off the the long-exposure function of the camera. The circuit diagram used in building this converter was based on Peter Katreniak’s K3CCDTools web page.


Signals sent through the serial port in the form of electrical pulses are used to activate electronic switches (transistors) required to properly operate a long-exposure camera

The conversion from USB port to serial port, and then serial port to parallel port is necessary since a direct USB port to parallel port conversion will simply not work since the direct conversion provided by commercially-available converters only creates a virtual port. While such converters work fine with printers (the task in which they were originally designed to flawlessly perform), they do not work well with telescopes and cameras since their hardware configuration cannot be used to energize any of the output pins in the simulated parallel port.

Related article:
DIY Autoguider: Home-built Autoguider Project
Testing ATIK-1HS II Long Exposure Mode (by James Kevin Ty)

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© Anthony Urbano (Manila, Philippines)