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From: dan@rna.UUCP (Dan Ts'o)
Newsgroups: net.graphics
Subject: Re: laser shows
Message-ID: <444@rna.UUCP>
Date: Thu, 10-Oct-85 15:53:54 EDT
Article-I.D.: rna.444
Posted: Thu Oct 10 15:53:54 1985
Date-Received: Sat, 12-Oct-85 07:47:51 EDT
References: <737@wdl1.UUCP>
Reply-To: dan@rna.UUCP (Dan Ts'o)
Organization: Rockefeller Neurobiology
Lines: 39

In article <737@wdl1.UUCP> jbn@wdl1.UUCP writes:
>
>      The basic idea is to use a loudspeaker driver to move the mirror;
>some rigs are as simple as a small bit of mirror glued to a loudspeaker
>cone.  But I'd like to hear more about what's commercially available.

	Well, that might produce interesting results, but that would not
allow any kind of 2D linearity. You could never produce the pretty 3 color
laser graphics animations shown at Siggraph, nor the regular oscilloscope-like
displays.

	The real thing uses mirrors on galvanometers. Such mirrors are produced
by a company in Watertown, Mass called General Scanning. They make drivers as
well, although you can drive the coils with a regular stereo hifi amplifier.

	Two mirror are used, each one mounted on a shaft that is driven by
a galvanometer. The mirror are placed one above the other, tilted and one
rotated by 45 degrees. This arrangement allows one coil to control the X
axis and the other to control the Y.

	You can drive the X axis with a waveform generator and the Y with your
music to produce a laser oscilloscope. It is best to filter out the high
frequencies and drive the Y mirrors with just the bass portion of the music
because the eye cannot follow the high frequency stuff. The mirrors themselves
have a frequency response from DC (if you use the right drivers) to about 1Khz.
To represent the high frequency portion of the music, you could drive the mirror
with the amplitude envelope (just like AM). I have never done this but it
should work.

	I hope this helps.
					Cheers,
					Dan Ts'o
					Dept. Neurobiology
					Rockefeller Univ.
					1230 York Ave.
					NY, NY 10021
					212-570-7671
					...cmcl2!rna!dan
					rna!dan@cmcl2.arpa