|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
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
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.