Parallel Port Interface to the Private Eye P4 Head-Mounted Display

Parallel Port Interface to the
Private Eye P4 Head-Mounted Display


The Private Eye P4 is a monochrome head mounted display manufactured by Reflection Technology in the early 1990's. The company seems to have gone out of business, but a sales brochure describing the device is available here, and a full set of developer's documentation lives here (permanent mirror here.) The display was distinguished by its relatively low price and high resolution (modern color micro-LCD HMD's are available with less than half the addressable pixels for several times the price.) It goes without saying that currently the Private Eye can only be obtained second-hand. The display has a resolution of 720x280 and talks through a proprietary serial interface. The CGA-compatible ISA video card which shipped with the device cannot be connected to most modern PCs (the screen shot below was taken with the card connected to a vintage single-board computer.) I contemplated designing a USB interface for the display, but was hampered by my inability (to date) of locating a HID class standard for displays (whether or not it exists, I will probably end up dreaming up my own protocol, since I will have to write the display driver from scratch anyway.) In order to experiment and see what various things will look like on the Private Eye, I built a trivial parallel port interface. This little dongle does not deserve its own page at all. This section is mostly a placeholder for the delicious USB-to-P4 schematics that will one day be posted.