View single post by Jeff
 Posted: Feb 10th, 2008 01:27 PM
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Jeff

 

Joined: Nov 7th, 2007
Location: Alabama USA
Posts: 127
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EVP_Babs wrote: Don't think I dropped off the face of the earth here. I am reading and trying to assimilate the knowledge.

The initial reason for asking if light blocked light was in relation to the theremin video that notemanz posted. I have seen quite a few theremin devices being sold on ebay which operate by something blocking a light cell. If a spirit is made of light and light can not block light than I would assume that anything that operates on that theory will be of no use.



Babs
Hey Babs.  I agree with your thoughts on a photo-sensitive arrangement.  Most phototransistors work on tight, filtered, infrared spectrum.  So any light energy outside of that spectrum would be ignored just because of the nature of the photo sensitive base of the transistor.  On those types of sensors, there is actually an infrared transmitter, and infrared receiver.  The transmitter is producing the infrared energy via a a lense that focuses the energy away from the receivers lense.  When something solid enough to reflect that energy comes withing that focused area, the beam is reflected back into the receiver.  This changes the receiver's gain into the amplifier it is feeding.  The closer the object, the more, or less gain is produced by the receiver.  In the case of the Theremin, the gain is decreased to lower the audio volume of the instrument.

The RF Theremin, which was the instrument I originally posted on, can sense proximity within its RF field.  This is why the thought occured to me in the first place.

Hope this helps!

Jeff