There are two problems with connecting a Limelight to a Macintosh II video
card:
1. The Macintosh II video card has a 15 pin DB-style female connector,
whereas the Limelight has a BNC female input.
2. The Macintosh II video signals are 35KHz for horizontal frequency and
66.67Hz for vertical scan rate. To properly display the video signal, a
bandwidth of 21 MHz for monochrome and 22MHz for color is needed. The
Limelight projector has a bandwidth of 20Mhz and a horizontal auto lock
maximum frequency of 33Khz
The first problem can be fixed with a specially configured cable. We wired
a Macintosh video cable to split the green signal on pin 5 to a BNC
connector. This cable allowed connection of both the monitor and the
projector. Another solution would be to contact Arizona Covid or Extron
Electronics. These companies manufacture break-out cables and converter
boxes. In this case, it would merely be a cable change. Although some
enhancements (vertical and horizontal picture centering or color
enhancement) are included in their converter boxes, this is not
particularly useful on a monochrome projector like the Limelight. Since
screen position controls are also supplied on the projector, a converter
will probably not be needed.
The second problem is not as easily dealt with without modifications to
the projector. Since its circuitry can not accept higher frequency data
rates, there is some image loss. Also, the plastic lens of the projector
can't focus all parts of the screen clearly, resulting in a good deal of
blurring on the edges. (A curved-back screen helps somewhat.) Though the
Limelight specification claims a maximum of 33 KHz for the horizontal scan
rate, the projector we tested was able to handle a full line of video from
the Macintosh at 35KHz. This may be a specification set below the
performance level on the projector -- however, the Macintosh scan
frequencies were pushing the limits of the projector: it took very little
adjustment to the horizontal control to lose the signal. A black box is
not likely to sharpen the image by modifying the signals, since the
problems are inherent in the projector's ability to handle the resolution.
As it stands, with a break-out cable the projector does display the
Macintosh II video, though the image may be objectionable to some.