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'SSU unit: Cheap Sonar, transmitter'
1997\11\16@163214 by Robert Nansel

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part 0 379 bytes
-BN



Attachment converted: wonderland:U2_Fig_1.GIF (GIFf/GKON) (0000BE73)
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  Country Robot            "Modular robot components
  69 S. Fremont Ave. # 2     for education and industry"
  Pittsburgh, PA 15202
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1997\11\16@182107 by Leon Heller

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Why have you sent me three postings with this unwanted crap!!!!


In message <v02140b01b09512990a4d@[204.171.126.30]>, Robert Nansel
<spam_OUTbnanselTakeThisOuTspamNAUTICOM.NET> writes
{Quote hidden}

--
Leon Heller: .....leonKILLspamspam@spam@lfheller.demon.co.uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM    Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/rcm.htm for details of a
low-cost reconfigurable computing module using the XC6216 FPGA

1997\11\16@184752 by Herbert Graf

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-----Original Message-----
From: Leon Heller <leonspamKILLspamLFHELLER.DEMON.CO.UK>
To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Date: Sunday, November 16, 1997 18:22
Subject: Re: SSU unit: Cheap Sonar, transmitter


>Why have you sent me three postings with this unwanted crap!!!!


   I guess I am now aware of your opinion on these postings, however, I
found them very interesting, and i have been looking for that kind of info
for quite a while now. I realize that it wasn't perhaps the most considerate
thing for this person to do, but I am sure I am not the only one who found
it nice to find it in my mailbox. TTYL

1997\11\16@215116 by Robert Nansel

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To anyone who was inconvenienced by my posting the GIFs of the ultrasonic
schematics: my apologies. I posted them because of the large number of
requests I received from other members of the list.

Perhaps a more constructive way to respond to this issue would be to define
what is "too large" a file to attach (or if one should attach files at
all).

I shall be guided by the collective opinion.



--BN

----------------------------------------------------------------------------
  Country Robot            "Modular robot components
  69 S. Fremont Ave. # 2     for education and industry"
  Pittsburgh, PA 15202
----------------------------------------------------------------------------

1997\11\17@071002 by Ron Kreymborg

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On Sun, 16 Nov 1997, Robert Nansel wrote:
> To anyone who was inconvenienced by my posting the GIFs of the ultrasonic
> schematics: my apologies. I posted them because of the large number of
> requests I received from other members of the list.
> Perhaps a more constructive way to respond to this issue would be to define
> what is "too large" a file to attach (or if one should attach files at
> all).
> I shall be guided by the collective opinion.
> --BN

A 56K attachment is fine by me. But then I'm using a big unix box
connected to the university 100baseT network. If I was on a 28K baud line
connected to a busy isp it would probably be a different matter. Perhaps
the question should be why was the attachment considered "crap"?

Ron

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ron Kreymborg                   Computer Systems Manager
Monash University               CRC for Southern Hemisphere Meteorology
Wellington Road
Clayton, VIC 3168               Phone     : 061-3-9905-9671
Australia                       Fax       : 061-3-9905-9689
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1997\11\17@102453 by Tom Rogers

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Since I thought the original discussion sort of asked for the details, I
thought the
posting was appropriate.

I vote to allow big attachments when solicited. Let the people with real
bandwidth
problems refuse attachments or limit their size in their email software or
at their
server.

--Tom Rogers  VP-R&D  Time Tech Inc.

{Original Message removed}

1997\11\17@105948 by myke predko

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Tom Rogers wrote:
>I vote to allow big attachments when solicited. Let the people with real
>bandwidth
>problems refuse attachments or limit their size in their email software or
>at their
>server.

This is assuming that people with bandwidth problems or who have to pay for
download bandwidth *can* change how their mailers work.  Some people don't
have the option of refusing attachments (or if they do, the attachment is
still downloaded to their PC - I know Eudora works that way).

What should have been done is to put the files on a server and let everybody
who wanted them download them at their leisure, rather than pushing them on
all 1200 of us.


If you have a large file that people have requested and you don't want to
send to each person individually and you don't have a web page or server
space for the file(s), it is appropriate to put a request on the list for
somebody to put it on their server.

I did this in the past and I always got two or three people willing to help
out.

myke

Check out "Programming and Customizing the PIC Microcontroller" at:

http://www.myke.com

1997\11\17@121625 by Sean Breheny

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Hello all,

I don't remember who posted it, but a few days ago, someone made a
suggestion that, instead of having the SSU time the time interval between
pulses, it just send a pulse whenever it receives an echo and count the
number of pulses it sends out. I think that this is a great idea because it
naturally provides for regular reporting intervals, i.e., the code could go
like this:

set up interrupt every 100 ms (or whatever delay you want)

a: send pulse
wait for receive pulse
when received, increment counter
goto a

interrupt:
send counter value
counter = 0
return

I will try this in my prototype.

Sean

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
http://www.people.cornell.edu/pages/shb7
Web Page Under Construction!
shb7spamspam_OUTcornell.edu

1997\11\17@134406 by mike

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In message  <01bcf367$01371760$64592581@bullgoose> @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
writes:
> Since I thought the original discussion sort of asked for the details, I
> thought the
> posting was appropriate.
>
> I vote to allow big attachments when solicited. Let the people with real
> bandwidth
> problems refuse attachments or limit their size in their email software or
> at their
> server.

I vote to send attachments direct to who ever solicits them.

As Andy Warren has pointed out, there are 1200 people on the list
if 100 people ask for the attachment, that leaves more than 10 times
that number who didn't ask for it.

Also, I, along with many others have no way of refusing large e-mails.
I don't pay by the byte, but I do pay the standard telephone charges.


Regards,

Mike Watson

1997\11\17@154926 by Eric van Es

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Tom Rogers wrote:

> Since I thought the original discussion sort of asked for the details, I
> thought the posting was appropriate.
>
> I vote to allow big attachments when solicited. Let the people with real
> bandwidth problems refuse attachments or limit their size in their email
> software or
> at their server.

OK - when solicted. But I think that one should consider other ppl too. I'm one
of those ppl that pay for time spent on the net. Since I got connected to the
web, our phone bill has gone up 3 times. If I can shave a minute of every time I
download my mail - I can have 3 more beers a month! Bargain!

I don't have much space on my ISP's server, but I'm willing to post images like
BN's. I'd rather do that than have certain characters loose all manners and
start throwing words like "moron" and "crap" around. This used to be a calm
list. No politics (mostly) & hate groups... Sometimes I write similar things
when ppl get me upset, but I never actually mail them.....

Anyway: Those same three files everyone got is also on my site if you loose
yours <G>

Cherio folks!

--
Eric van Es               | Cape Town, South Africa
KILLspamvanesKILLspamspamilink.nis.za | http://www.nis.za/~vanes
LOOKING FOR TEMPORARY / HOLIDAY ACCOMODATION?
http://www.nis.za/~vanes/accom.htm

1997\11\17@184403 by Engineering Department

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<Ron Kreymborg writes about the large attachment: >
> Perhaps  the question should be why was the attachment
> considered "crap"?

My thoughts exactly.  Ill advised perhaps, but
certainly not "crap".

Win Wiencke
Image Logic Corporation

1997\11\18@024710 by Mike Ghormley

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Sean Breheny wrote:

>I don't remember who posted it, but a few days ago, someone made a
>suggestion that, instead of having the SSU time the time interval
>between pulses, it just send a pulse whenever it receives an echo and
>count the number of pulses it sends out. I think that this is a great
>idea <SNIP>

Sean,

I think that there might be a fly in the ointment in the "count the
pulses scheme."  While it will work fine for finding the distance from
the transducer to a single object like a wall, my students found out that
in a "real world" environment (moving around the lab) there were multiple
echoes coming back at varying times from various objects within the
transducer's cone.  Depending on the settling time of your tank circuit
you might get a lot of ghost hits.  A single metal legged stool would
give us four hits per ping, for instance.

While I am on the subject, let me put out a couple more ideas that might
be useful as no one seems to be posting something similar.

Use piezo transducers as they will eliminate a *lot* of
frequency-dependant circuitry.  Also, it is such a high-Q device that you
can hit it with almost any short pulse and it will resonate at its center
frequency without much help.

Use a darlington transistor to drive the transmitting piezo element.  You
can drive the darlington straight off of a CPU pin.

Hit a 40kHz transducer with a 12.5uS (1/2 40kHz period) pulse for the
best results.  At least that is what we found with (I believe) Murata
transducers.

We tried making an op-amp gain block for the receiver that had a
logarithmic gain over time, and then start its ramp after a ping but
found it too much trouble for us.  We mistakenly thought that the
amplitude of the signal might give us useful positioning information, but
it only seemed to tell us about the area of the reflective surface and
its hardness.  Varnished wood had stonger signals than plain wood of the
same area, for instance.  We settled on an AGC circuit to pump up weak
signals.

We tried some one-chip Tx/Rx devices (I seem to remember a TI and an NS
part, but I don't recall the numbers) but found that the Tx and Rx
sections shared a common resonant circuit and that minimum distances were
limited to around 6-8" due to the settling time of the tank circuit.

Just some thoughts...

Michael

1997\11\18@075200 by Sean Breheny

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Hmmmm,

I see what you mean about the multipath problem.

Sean




At 11:45 PM 11/17/96 -0800, you wrote:
{Quote hidden}

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
http://www.people.cornell.edu/pages/shb7
Web Page Under Construction!
RemoveMEshb7TakeThisOuTspamcornell.edu

1997\11\18@135039 by Tim Kerby

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Hi
Multipath should not be too much of a problem if the beam is collimated and
the first ping is the one taken count of.


Tim




At 07:50 18/11/97 -0500, you wrote:
{Quote hidden}

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1997\11\19@015753 by Mike Ghormley

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Tim Kerby wrote:

>Multipath should not be too much of a problem if the beam is collimated
>and the first ping is the one taken count of.

You are right Tim, but Sean was looking at a different scheme which had
the problem I posted.

The scheme was to zero a counter and then send a ping.  As soon as an
echo was detected, the counter was incremented and another ping was
immediately sent -- then another, and another...

Then after a set amount of time the number of pings would be counted to
determine the distance from an object.  The counter would then be zeroed
and the loop would begin again.  Thus, my caveat about multiple echo
returns.

From what little experience I had, the surest method to measure to the
closest object is to send the ping and measure the time for the first
return, as you suggested.  It is then wise to wait to send the next ping
until no echo could possibly return and be detected.  We did some trial
and error to find the appropriate time, but found that a large metal door
would return a detectable echo a great distances in a concrete corridor.
We shortened the time between pings by zapping the AGC gain back down to
1:1 which killed any distant echoes.

Another idea we were going to try was to send out 3 pings, then we would
send out 4 pings, then 5, then 3, then 4, etc.  We were going to count
the number of return pings to see if we were looking at the current ping
or a previous one.  Unfortunately, I resigned before the idea was carried
out, so I don't know how practical it is.

Michael

1997\11\19@084609 by Tom Rogers

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Collimated is the wrong term here. Unlike light, it's a real stretch to get
to the particle-like behavior of sound. Designing mechanical components
based on the idea that the wave-like nature of the "beam" is similar to
light will also be less than satisfactory. The math is fairly exotic but
do-able for linear uncompressible media, but air doesn't fit that
description.

For this project I would (again) strongly advise examining existing
successful systems and emulating them.

--Tom Rogers  VP-R&D  Time Tech Inc.

-----Original Message-----
From: Tim Kerby <RemoveMEtim.kerbyspamTakeThisOuTUKONLINE.CO.UK>

>Multipath should not be too much of a problem if the beam is collimated and
>the first ping is the one taken count of.

1997\11\19@095508 by 'Grif' w. keith griffith

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At 22:55 11/18/96 -0800, you wrote:
>Tim Kerby wrote:
>
>>Multipath should not be too much of a problem if the beam is collimated
>>and the first ping is the one taken count of.

Don't forget the shallow water problem,,, that is the second bounce.  Don't
know how big a problem it'll be for air,,, but a hull in shallow water will
show a second image at twice the distance to the physical bottom.  Yea,,, I
know,,,,  cheap fish finder  ;-)



'Grif' N7IVS

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