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The Virtual Reality Homebrewer's Handbook
Paperback/CD-ROM Set Published by John Wiley and Sons
£24.95 UK, $39.95 US, $55.95 CAN
Biocular Head Mounted Display
This has got to be one of the easiest HMDs to build ever! Itís built along similar lines to the last project, but uses a fresnel lens in front of both eyes, instead of a glass lens in front on one eye. If youíre buying new parts for this project, read the notes in the last project about choosing LCD TVs and PC to video converters.
Fresnel lenses can be made up on plastic as a series of concentric circles. Each circle is like part of a normal lens, but has had everything except for the curve on the surface removed. This means you can have a flexible flat plastic sheet with the magnifying capabilities of a much bigger solid lens. Fresnel lenses are available in all sizes, some even as large as a man. The credit card size versions used in this project are available cheaply (£/$1.50) from opticians and other places as hand held magnifiers, and usually offer a three times magnification. An extra feature of fresnel lenses is their ability to bend light like a prism, when it passes through away from the centre of the circles. Itís this property that allows us to use both eyes with a single lens in this project.
Important Note: Fresnel lenses are not recommended for extended use as they will cause eye strain. Therefore, be reasonable about the length of time you use this HMD for, and take regular breaks if you need to use it for long periods.
Figure 4. 1 - Assembly of the Biocular HMD
Building the Biocular HMD
Make the enclosure
A cardboard enclosure is used to separate the lens the required distance from the LCD screen, and block out external light. Use cardboard thick enough to keep its shape, and either get matt black card, or colour the inside of the enclosure matt black before you use it (this stops reflected light). Mark out the template on the cardboard, using measurements from your TV screen and fresnel lens. Experiment beforehand to find the necessary distance between the lens and the LCD screen (40mm in my unit), remembering to keep the centre of the circles on the lens between your eyes, and the lens with the rough side towards, and the smooth side away from, your eyes. After marking the template, cut along the solid lines, and score along the dotted lines. You should then be able to fold the cardboard into a box, open at both ends, and narrower at one end than the other. Use glue on the single tag on the side to hold the enclosure together. Bend the tags on the open ends outwards.
Figure 4. 2 - Enclosure Template for Biocular HMD
Cut a rectangular hole in the lens of the goggles, centred between the eyes, and slightly smaller than the size of the fresnel lens.
Paint the lens of the goggles matt black to stop any light entering. Welding goggles should be light-proof around the edges, but if they are not, or you are using transparent safety goggles, then paint the edges black. If you canít stop the light coming in with the paint, try covering the goggles with insulation tape.
Glue the fresnel lens to the outside of the goggles lens over the previously cut hole. Make sure that the fresnel lens is placed so that the circles on it are centred between the eyes, and the rough side, not the smooth, is facing the eyes.
Glue the enclosure onto the goggles lens over the fresnel lens. Make sure you put the enclosure on the correct way round with the end cut to fresnel lens size over the lens. The tags on the enclosure should be bent outwards and used to glue it to the goggles lens. You may need to cut a slot in the bottom of the enclosure for it to fit around your nose. This is best measured by trial and error.
Glue or tape the other end of the enclosure to the TV screen. Glue is more secure, but adhesive tape means that you can get your TV back unharmed later.
If you find the enclosure cannot support the weight of the HMD well, try drilling 4 small holes in the goggles lens, 2 either side of the enclosure. A piece of string or thin wire can then be used to tie the TV to the goggles, supporting much of the weight.
Connect the TV to your PC via the PC to video converter. Turn on the TV, put on the goggles and enjoy! If the goggles keep slipping because of the weight of the HMD, try running another elastic strip from the TV, over your head to the goggle elastic.