Re: Dissolves for 3-D projectors

[michaelk@xxxxxxxxxxx (Michael Kersenbrock)]

> George, you may have your next product in-line.....how about going down to
> the R & D dept. at Themelis International and talking with the folks about a
> dissolver that would operate with two of any old style projectors......like
> your viewer power supplies...where you bypass the on- off button on the
> viewer,
> (great option for those old Revere viewers where the button spring is either
> broken or corroded from battery acid)
> I know this is not as simple as it sounds, but take a couple of older
> projectors.....say a Compco, and a TDC, and figure a way to get into the
> power that is supplied to the bulbs.....provide a rheostat so that you can
> fade up on one image....and fade down on the other.....boy would that open a

Actually, that'd be a pretty simple device.  To minimize liablity problems
and for neatness as well, it'd have to be a universally installable option
that's installable inside of various projectors.  This way the line-power
stays in the unit, and only low voltage control signals come out to hook between
units (to make them synchronize) or to an external device connected to a tape
recorder doing the control.

The fader just needs to be a "thyristor" (actually, a triac or related device)
with a control circuit that has a decay shape that takes into account the 
rapid brightness drop-off of a "nominal" projection lamp vs. effective RMS voltage.
It also needs to provide some isolation, perhaps optical for the off/on signal that
exits the projector.  I recall there being some optically isolated "solid state
relays" but I don't recall there being fade control -- so the device may have to
be discretely built.

A small circuit board would probably do.  Each projector would connect to a
small control box that could be powered off of one of those blocks-on-the-wall
type power units and connect to 'n' projectors.  Would take simple circuitry to
have it fade and move to the next projector upon a 'beep' from the tape
recorder, and of course one could use different tones to make it go forward,
backwards, all-off, or whatever. Perhaps an on-tone and an off-tone for each
channel.  Perhaps with two speeds of fade (fast/slow) for each.

Actually, if one uses one of those cheapie microcomputers ($5~10 variety in
lowish quantity) in the central controller, it could pulse-width-modulate
a binary signal on that optically isolated line to easily change the brightness 
at varying rates as well as changing the various channels simultaneously or
in controlled sequences.  That would give total continuous control but still
have the control lead be binary.

The projectors and their bulbs would probably need to have a basic match like
the two halves of a single projector -- at least to the extent of general brightness
and bulb type to keep bulb color and brightness matched when switching from
one to another without color bias changes.  One could control any projector, but one 
might want to have only multiples of the same kind being together for best performance,
or at least "in public". :-)

It'd be time consuming for all the physical building (circuit boards,etc) aspects,
although conceptually and electrical-design-wise it'd be simple.  If one were to
do this commercially, one would wonder about liablities and U.L. approvals, and
such though.  And maybe FCC emissions testing as well.  But for one's own kitchen
table.... :-)

Of course, having only one stereo projector, such a project would be *REALLY*
low on my  'round tuite list -- which is already long enough to last me a good 
while. Should I ever get a second projector, I'll add the project to my list
and I'll let everybody else have the circuitry if someone hasn't already done
I get to it (which is *very* likely  :-).

Is this what you meant by brainstorming?


Mike K.


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