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- Newsgroups: sci.electronics
- Path: sparky!uunet!pipex!bnr.co.uk!bmdhh243!michthom
- From: michthom@bnr.ca (Michael Thomson)
- Subject: Re: Elec-Mag Rad
- Message-ID: <1992Dec16.123411.22879@bnr.uk>
- Sender: news@bnr.uk (News Administrator)
- Nntp-Posting-Host: bmdhh255
- Organization: BNR Europe Ltd, Maidenhead, UK
- X-Newsreader: TIN [version 1.1 PL8]
- References: <1gm4rhINN7vl@uwm.edu>
- Date: Wed, 16 Dec 1992 12:34:11 GMT
- Lines: 58
-
- Chad Edward Albrecht (albrecht@csd4.csd.uwm.edu) wrote:
- : 1) ...I need to measure distances within .001 of an inch ... It needs to
- : be a fairly long wavelength, so as to not give me cancer!
- : I will ... have each transmitter send a slightly different frequency
- : and the same receiver distinghush between them.
-
- I'm not sure exactly what you're after, but I think your expectations are
- rather higher than you will be able to achieve easily. Why have you decided on
- such a high level of accuracy? You can't hold your hand still to anything like
- that precision, so why measure it? Assuming you are working in a coordinate
- system, 20 feet on a side, you'll be working in a space 240000 pixels on a
- side, or a volume of 1.38x10^16 points! I hope you've got some nifty hardware!
- That's a LOT of points to recalculate every frame!
-
- Also I think you're wanting to use RF(Radio Frequency) signals for the
- measurements. This is tricky stuff to set up, and extracting several
- close-packed frequencies will be a nightmare!
-
- I think a much more realisable scheme would be based on ultrasound. You then
- require one transmitter, and four recievers to fix the transmitter's position
- in an x,y,z coordinate system. Generate an ultrasonic chirp, and time the delay
- before each reciever gets it. The propagation speed of sound in air is *MUCH*
- slower than RF, so you should be able to do this with a micro (but watch out
- for return signals from two detectors arriving very close together!!)
-
- The delay varies with distance, and sound travels at 330m/s in air. That means
- 33 cm/ms or 3.3 mm every 10 microseconds. I really believe that an accuracy of
- 5 mm will be PLENTY! This assumes that you can check for the return signals
- every 10 microseconds, which is not difficult on a decent PC.
-
- I don't know how you plan to measure the orientation of the transmitter point -
- I really don't have very good suggestions here. A joystick-type affair would
- give you pitch and roll information, but it isn't much help with rotation about
- an axis perpendicular to the floor! Sorry I can't be more helpful!
-
- I would only take a position reading about twice a second, because you'll need
- the CPU time to triangulate the position, and redraw the screen. THIS WILL TAKE
- TIME!
-
- In summary, I would advise you to think VERY carefully about what you NEED to
- get out of this system. If you have limited time for this project, make sure
- you have achievable goals, or at least realistic ones! Your assessors are more
- concerned with the way you tackle the problem than its eventual solution! Don't
- try to build a system that does everything. Spend your time on getting a simple
- system that works well, and approach it sensibly. You will reap the rewards in
- a much better assessment than if you pack in all the features you can think of,
- don't quite get it working, and the whole system is a mass of patches and bugs
- waiting to get out.
-
- Hope this is of some help. Sorry I can't E-mail! All the best for a very
- interesting and challenging project!
- --
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- + Michael Thomson + The opinions expressed here, while definitely NOT +
- + + those of my employer, may OR MAY NOT be mine! +
- + BNR Europe Limited + --------------------------==========-------------- +
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