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From: jkh@meepmeep.pcs.com (Jordan K. Hubbard)
Newsgroups: sci.electronics
Subject: Re: sensory substitution
Message-ID: <1990Feb5.162926.3877@pcsbst.pcs.com>
Date: 5 Feb 90 16:29:26 GMT
Reply-To: jkh@meepmeep.pcs.com (Jordan K. Hubbard)
Organization: PCS Computer Systeme, GmbH
Lines: 55

You'll probably want to talk to the Smith-Kettlewell Institute
of Visual Research in San Francisco. They've done a lot of interesting
things for the blind. One of the things they had that impressed me
(at least in concept, the implementation still had a few rought edges) by
its general simplicity was a system for indicating the room
numbers by broadcasting a recording of the room number ("one-oh-three...
one-oh-three..one-oh-three..") over an IR led mounted above the door
frame. A small receiver would pick up the broadcasted signal and
decode it (presumably into an earphone). It seems that a simple
unit could be built to announce just about everything ("Emergency
exit..", "Mens room..", "Harry's bar".. etc) using an IR led (TIL32 or
equiv), a small ROM and some glue logic. I think the SKIVS system
used tape, but nowadays you can get at least 20 seconds of reasonable
quality sound into one ROM, using compression [and the current high capacity
of ROMs]. The biggest problem to overcome is getting the receiver and/or
transmitter to work reliably given the various forms of light interference 
and angles of reflection involved.

This brings me to my main question, however..

Here in Munich, during the summer evenings, we have lots of Bats
that congregate over the river to munch on winged insects and other
savory morsels. I've often sat watching them swooping around, wishing
that I could somehow eavesdrop on their guidance signals and see how and
when they "ping" their targets. Questions:

1. What is the frequency range and average amplitude of bat radar?

2. What sort of microphone(s) would be best? If bat radar is fairly
   low amplitude, should I build a parabolic mike? How does one properly
   design a parabolic dish for a given freqency range? I probably don't
   want to go for omnidirectional sensitivity anyway, since that would
   make it impossible to track a single bat diving after an insect.

3. What sort of frequency converter circuitry would I need?

The ideal setup would be a small box containing the electronics and
batteries with a jack for a pair of headphones to monitor the
down-shifted signals and a jack for some sort of pistol-grip mounted
mike that I could point at areas of interest.

Sorry if these questions are a bit simplistic, I'm afraid my expertise
lies more in software than hardware.

Any and all help would be much appreciated. I'd be happy to forward
any information I get to other interested parties (I suspect that it's
a somewhat esoteric area of interest, however).

					Jordan Hubbard
					jkh@meepmeep.pcs.com
					Munich, West Germany
			PCS Computer Systeme GmbH, Munich, West Germany
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