Alt-BEAM Archive
Message #07354
To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Wed, 3 Nov 1999 17:08:14 -0800
Subject: [alt-beam] Re: directional can of worms
Wowza!
I really like your sound BEAM thought experiments Jacob! What was the output
from the Polaroid range finder unit?
I played a bit with ultrasonic intrusion alarms but they use doppler shift
to detect motion and are pretty useless for this application.
A surplus motion detector may be a cheap source of ultrasonic transducers
though. I suggest a combination sound click and IR flash could be used to
get direction and range by measuring the delay between those two signals
(speed of light vs speed of sound). heheh!
regards
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411
> -----Original Message-----
> From: Jacob Booth [SMTP:j.booth@mary.acu.edu.au]
> Sent: Wednesday, November 03, 1999 4:32 PM
> To: beam@corp.sgi.com
> Subject: directional can of worms
>
> There are many ways of direction finding with RF. Not necessarily easy
> ones, as thing just happen too fast. No one has yet mentioned the fact
> that
> in a beam type environment, reflections and shadow areas would be far too
> common. Don't get me wrong, I am not poo-pooing the idea at all; I would
> like to have a tracking station that I could use to monitor my bot's
> motion
> on my pc (so I could see what it was up to during the day.
>
> I have a video camera hooked up for time lapse, but that just ain't as fun
> :). That would help on the size problem, as the bot would be sending out
> the beacon, and the antenna system could be set around it's operating area
> at a more manageable distance.
>
> I think triangulation error would still be rather inaccurate at this kind
> of scale. Finding a ship at sea would be easier than finding my bot under
> the sofa :)
>
> Maybe (and boy, am I going to open a can of worms here, and reopen some
> long dead threads) the good old 40khz AUDIO transducers would be of some
> use here. The 'beam' of audio is quite directional, and things happen at
> an
> order of magnitude slower in audio. I know polaroid made some fantastic
> units (complete, with transducer and driver/rx board) that we used on some
> prototype bitumen laying machinery. This stuff was VERY accurate (had
> temperature compensation etc) to within 1-2 mm over a 1.5 metre range. The
> range was extensible, with a similar extension on the accuracy (eg 15 m
> range 1-2 cm accruracy. Not bad at all really). Unfortunately they stopped
> production of the unit. You can still get the transducer (they still use
> them in the autofocus of their cameras) but they needed some bizzare
> voltages to run (300v pulse to transmit etc). We tryed to build the driver
> boards ourselves, but just couldn't copy the quality or repeatability.
> They
> also used custom ic's :(
>
> So what was I saying? Oh, yeah, uh, so sound can be used instead of RF in
> short-range projects. PIcture 3-4 mikes around a room, hooked up to some
> sort of differential op-amp stage and a pc, the bot wandering about
> 'barking'. And then picture the PC drawing a trace of the bot wandering
> about the screen. Maybe different tones (or even DTMF) so the bot can
> communicate what it is 'thinking'.
>
> Well, thats got my two typing fingers tired.
>
> cheers
> Jacob
> ------------------------------------------------------------------
> Jacob Booth BIS, MCP Web http://www.its.mary.acu.edu.au/
> IT Services Email j.booth@mary.acu.edu.au
> Phone (02) 97392235 Fax (02) 97392924
> Australian Catholic University - MSM Campus Strathfield NSW
7355 Wed, 3 Nov 1999 20:25:18 -0500 PBS - no Mark! Dave Hrynkiw
> Hmmm. Sorry guys, but it looks like they didn't use his footage, and used
a
> lot more time on the robocup soccer instead. Can't blame them - the
robocup
> stuff was amazing!
>
> Regards,
> Dave
> ---------------------------------------------------------------
> "Um, no - that's H,R,Y,N,K,I,W. No, not K,I,U,U, K,I,_W_. Yes,
> that's right. Yes, I know it looks like "HOCKYRINK." Yup, only
> 2 vowels. Pronounciation? _SMITH_".
> http://www.solarbotics.com
>
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