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'Serial Sonar Unit kit proposal - feedback requeste'
1997\11\10@190006 by Rick Dickinson

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I've seen quite a large number of postings by people looking for sonar devices
for robotics use.  The commonly suggested solution (the Polaroid sonar module)
has several drawbacks, however: 1) it's expensive ($50 each or so), 2) it needs
modifications to measure short distances, 3) the transducer used is fairly
large (1.25" or so diameter), and 4) your processor gets tied up calulating the
range by timing the reflected chirp.

Owing to the success of the various serial LCD "backpack"-type devices, I
thought it would be useful to develop a low-cost kit for an ultrasonic ranging
unit, that could be accessed using some simple serial protocol.  I envision
this "Serial Sonar Unit" (SSU) being a small PIC-based PC board, with
connections to a pair of Murata 40 KHz transducers like the ones sold by All
Electronics for $2.50 a pair.

The SSU would have two modes: continuous reading, and on-command.  If set to
continuous mode, the SSU would continually send out, and time the echos of,
tone bursts, storing the most recent result internally.  When polled, it would
return the most recent reading.  In on-command mode, the SSU would wait for a
"go" command of some sort, then send a pulse and time its return.  If polled
before the measurement was complete, it would return some sort of "busy"
indication.  If polled after the measurement was complete, it would return the
measurement.

My intent is to come up with a design that will save my fellow hobbyists some
time and money, and will make it easy to incorporate sonar ranging into PIC and
other small microcontroller-based projects.  Offloading the timing, transducer
drive, and calculation tasks to a dedicated SSU will allow the programmer to
concentrate on the tasks to be done, not the ranging implementation.  Allowing
single-shot or continuous ranging will allow simpler implementations to use the
continuous mode, and multiple-unit configurations to use single-shot mode to
avoid interference between transducer pairs.

Details to be ironed out include:
 -  Protocol for commands, including mode changes
 -  Data format for measurement data returned
      Inches?
      Milli/microseconds?
      Binary or BCD?
 -  I2C, SPI, or none of the above
 -  Baud rate/clocking (async 9600/4800/2400/1200? Autobaud? Sync?)
 -  Distribution mechanism
      PIC code/Schematics/PCB layout on web for download?
      Preprogrammed PICs and etched PCBs for purchase?
      Both?

I am just at the "fleshing out the idea" stage, and I would appreciate any
feedback as to whether or not anyone would be interested in such a device.
Also, I want the SSU to be as useful as possible, so I would love to hear
everyone's input on the implementation details I outlined above.  I figure that
the discussion would be most valuable if everyone could participate, so please
send replies to the PICLIST instead of directly to me.

Thanks in advance,

- Rick Dickinson
+--------------------------------+------------------------------+
| Rick "The Notes Guy" Dickinson | Views expressed by the author|
| Lotus Notes & Domino Solutions | are not necessarily those of |
| (818)563-1061 spam_OUTrtdTakeThisOuTspamnotesguy.com | Enterprise ArchiTechs.  They |
|   http://www.eArchiTechs.com   | might not even be mine....   |
+--------------------------------+------------------------------+

1997\11\10@204451 by Fred Hansen

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Good Evening Picsters

Sonar rangefinding is a common thread and
often generates a lot of interest but not
a complete project. Rick's idea is quite
good, I nominate him Project Leader.

Have you seen the August Issue of Circuit
Celler (page 76) where Jeff Bachiochi uses
a Sharp GP1U5 IR receiver and replaced the
IR sensor part with an ultrasonic transducer?
A great idea, check it out!

Count me in Rick!

Fred Hansen     Research Scientist
NYU Center for Advanced Technology
http://www.cat.nyu.edu

1997\11\10@221540 by Ian Raymond Douglas

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G'Day Rick
    I for one would be veeeery interested.
                           Regards, Ian Douglas

1997\11\10@235904 by Alberto Smulders

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Hi Rick !!!

Another very interested person here, looking for a cheap method to measure
contents in grain and oil storage bins - should be a kind of ultrasonic
rangefinder, maximum range around 10...12 meters, ruggedized for use in an
industrial environment, some serial communication means for rather long
distance (up to 1 km or so) if possible with unique address for
interrogation, and.... (hmmm... am I asking too much ????)

Regards

Albert Smulders
InSAD - Encarnacion, Paraguay
.....insadKILLspamspam@spam@itacom.com.py

1997\11\11@002358 by tjaart

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Alberto Smulders wrote:
>
> Hi Rick !!!
>
> Another very interested person here, looking for a cheap method to measure
> contents in grain and oil storage bins - should be a kind of ultrasonic
> rangefinder, maximum range around 10...12 meters, ruggedized for use in an

I've often wondered if one can't use a speaker to see at which frequency
it resonates to measure the empty space in vessels like these. Another
application would be a pertol tank.

Has anyone tried this?

--
Friendly Regards

Tjaart van der Walt
tjaartspamKILLspamwasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
|    Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973    |
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|_____________________________________________________________|

1997\11\11@121341 by Rick Dickinson

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At 08:32 PM 11/10/97 EST, Fred Hansen <.....hansenKILLspamspam.....CAT.NYU.EDU> wrote:
>Good Evening Picsters
>
>Sonar rangefinding is a common thread and
>often generates a lot of interest but not
>a complete project. Rick's idea is quite
>good, I nominate him Project Leader.

Oh, how fun.... :-)

But seriously, what sort of interface/protocol would be appropriate?  What
format would you prefer the ranging data to be in?

>Have you seen the August Issue of Circuit
>Celler (page 76) where Jeff Bachiochi uses
>a Sharp GP1U5 IR receiver and replaced the
>IR sensor part with an ultrasonic transducer?
>A great idea, check it out!

Interesting idea.  Are there any details online anywhere?

>Count me in Rick!

Okay, Fred.  Your first task is to tell me what your personal "dream specs" for
an SSU would be.  How would you like it to work to make your life easiest?
What sort of granularity of measurement is needed?  Is 8 bits enough? Is 16
bits too many?  Would you like the results scaled to inches? cm? metres? left
as a raw count?  Should the data be presented in binary? ASCII? packed BCD?
EBCDIC?

- Rick "So many questions" Dickinson
+--------------------------------+------------------------------+
| Rick "The Notes Guy" Dickinson | Views expressed by the author|
| Lotus Notes & Domino Solutions | are not necessarily those of |
| (818)563-1061 EraseMErtdspam_OUTspamTakeThisOuTnotesguy.com | Enterprise ArchiTechs.  They |
|   http://www.eArchiTechs.com   | might not even be mine....   |
+--------------------------------+------------------------------+

1997\11\11@122036 by Rick Dickinson

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At 02:13 PM 11/11/97 +1100, Ian Raymond Douglas wrote:
>G'Day Rick
>     I for one would be veeeery interested.
>                            Regards, Ian Douglas

Interested in helping design, obtaining a unit after it's designed, or both?

Tell me what sort of specs your "dream SSU" would have?  How much granularity is
needed in the measurement?  What maximum range is appropriate?  How should
results be returned (binary/BCD/ASCII/etc.)?

- Rick "So many questions" Dickinson

+--------------------------------+------------------------------+
| Rick "The Notes Guy" Dickinson | Views expressed by the author|
| Lotus Notes & Domino Solutions | are not necessarily those of |
| (818)563-1061 rtdspamspam_OUTnotesguy.com | Enterprise ArchiTechs.  They |
|   http://www.eArchiTechs.com   | might not even be mine....   |
+--------------------------------+------------------------------+

1997\11\11@123248 by Rick Dickinson

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At 01:57 AM 11/11/97 -0400, Alberto Smulders wrote:
>Hi Rick !!!
>
>Another very interested person here, looking for a cheap method to measure
>contents in grain and oil storage bins - should be a kind of ultrasonic
>rangefinder, maximum range around 10...12 meters, ruggedized for use in an
>industrial environment, some serial communication means for rather long
>distance (up to 1 km or so) if possible with unique address for
>interrogation, and.... (hmmm... am I asking too much ????)

Hmmmm... I suppose that, as a kit, it would be a simple matter to ruggedize the
SSU by simply putting the circuit in a sturdy project box of some sort and
epoxy potting it.  The transducers could be mounted on the end of a cable to
allow easier positioning, with the "control" circuitry mounted nearby.

As far as the serial drive capability goes, I was planning on using TTL levels
to make microcontroller interfacing easier.  However, Maxim and other companies
make a number of chips for level conversion (the MAX232 springs to mind), so
just about any sort of line drivers could be added without much trouble (RS232,
RS485, etc.).

Since this is to be a kit, maybe allowing a "poll address" to be set by
programming an EEPROM location would solve your addressability issue.

What sort of granularity would you need in the measurement?  In other words, how
big of a "step size" is needed between readings?

- Rick "So many details to mail down" Dickinson

+--------------------------------+------------------------------+
| Rick "The Notes Guy" Dickinson | Views expressed by the author|
| Lotus Notes & Domino Solutions | are not necessarily those of |
| (818)563-1061 @spam@rtdKILLspamspamnotesguy.com | Enterprise ArchiTechs.  They |
|   http://www.eArchiTechs.com   | might not even be mine....   |
+--------------------------------+------------------------------+

1997\11\11@131609 by Alessandro Zummo

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Il 11-Nov-97, Rick Dickinson scrisse:

> unit, that could be accessed using some simple serial protocol.  I envision
> this "Serial Sonar Unit" (SSU) being a small PIC-based PC board, with
> connections to a pair of Murata 40 KHz transducers like the ones sold by All
> Electronics for $2.50 a pair.

I'm really interested...

>Details to be ironed out include:
>  -  Protocol for commands, including mode changes
>  -  Data format for measurement data returned
>       Inches?

better using cm.

>  -  I2C, SPI, or none of the above

I2c would be fine...

>  -  Baud rate/clocking (async 9600/4800/2400/1200? Autobaud? Sync?)

Fixed, say at 9600...

>  -  Distribution mechanism
>       PIC code/Schematics/PCB layout on web for download?
>       Preprogrammed PICs and etched PCBs for purchase?
>       Both?

In my opinion it should first come out in the first version (i.e. on web) and
then,
if needed in the second...


--

  - *Alex* -

     (KILLspamazummoKILLspamspamita.flashnet.it)

1997\11\11@131614 by Alessandro Zummo

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Il 11-Nov-97, Alberto Smulders scrisse:

>Another very interested person here, looking for a cheap method to measure
>contents in grain and oil storage bins - should be a kind of ultrasonic
>rangefinder, maximum range around 10...12 meters, ruggedized for use in an
>industrial environment, some serial communication means for rather long
>distance (up to 1 km or so) if possible with unique address for
>interrogation, and.... (hmmm... am I asking too much ????)

After a standard ultrasonic module has been defined you can even
add your own code to drive a fiber optic trasmission systemmm...

The main target should be to build that module.

--

  - *Alex* -

     (RemoveMEazummoTakeThisOuTspamita.flashnet.it)

1997\11\11@133150 by Rick Dickinson

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At 01:33 PM 11/11/97 +0100, Alessandro Zummo wrote:
>Il 11-Nov-97, Rick Dickinson scrisse:
>
[snip proposal for SSU]
>
>I'm really interested...
>
>>Details to be ironed out include:
>>  -  Protocol for commands, including mode changes
>>  -  Data format for measurement data returned
>>       Inches?
>
>better using cm.

What sort of granularity would be needed, and what is a reasonable maximum
range?  I want to avoid having to do any sort of AGC, so the range would have
to be known in advance to set the amp gain on the receiving transducer.

>
>>  -  I2C, SPI, or none of the above
>
>I2c would be fine...
>
>>  -  Baud rate/clocking (async 9600/4800/2400/1200? Autobaud? Sync?)
>
>Fixed, say at 9600...

I have been doing a little bit of design brainstorming, and have an idea or two
about implementing the interface portion.  I'll write up my ideas in another
post.

>
>>  -  Distribution mechanism
>>       PIC code/Schematics/PCB layout on web for download?
>>       Preprogrammed PICs and etched PCBs for purchase?
>>       Both?
>
>In my opinion it should first come out in the first version (i.e. on web) and
>then,
> if needed in the second...

I tend to agree.  I'd like to make this a collaborative effort with other
PIC-Listers, and make the design available freely to anyone with the resources
to build it.

- Rick
+--------------------------------+------------------------------+
| Rick "The Notes Guy" Dickinson | Views expressed by the author|
| Lotus Notes & Domino Solutions | are not necessarily those of |
| (818)563-1061 spamBeGonertdspamBeGonespamnotesguy.com | Enterprise ArchiTechs.  They |
|   http://www.eArchiTechs.com   | might not even be mine....   |
+--------------------------------+------------------------------+

1997\11\11@144926 by Robert Nansel

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>...Your first task is to tell me what your personal "dream specs" for
> an SSU would be.  How would you like it to work to make your life easiest?
> What sort of granularity of measurement is needed?  Is 8 bits enough? Is 16
> bits too many?  Would you like the results scaled to inches? cm? metres? left
> as a raw count?  Should the data be presented in binary? ASCII? packed BCD?
> EBCDIC?
>
> - Rick "So many questions" Dickinson


Here's my wish list: I would like the SSU to use an I2C interface, with the
possibility to configure it to do the following:

1) Use Hardware General Call to periodically broadcast range readings to
the bus; this has the advantage that the SSU code wouldn't need to know
anything about the other nodes on the bus. Instead, the SSU would transmit
as a master the I2C addr. "00000000" followed by "AAAAAAA1", where
"AAAAAAA" its own address, then the range data. This mode should be
programmable for update rates varying from, say, 16 Hz to 0.0625 Hz.

2) Respond as slave to direct addressing requests to: a) configure update
rate & mode; b) return range reading now; c) configure setpoints.

3) Broadcast Hardware General Call when high or low setpoints are crossed.

4) A variant of 3: Broadcast Hardware General Call on delta.


Data returned: Time Of Flight (TOF) to nearest half millisecond in binary.
Second choice would be BCD. Use TOF instead of absolute distance because
seconds are the same in MKS and Conventional units, and each node can scale
this into desired range units if needed. Also, you can adjust for
temperature & altitude effects more readily.

For many applications, 8-bit resolution would be entirely adequate, which
would correspond to a dynamic range of approx. 3.0" to 844" (7.6 cm to 2140
cm), with the usable band of commonly available transducers being from 6"
to 360" (15 cm to 914 cm). If you choose BCD, though, you might as well use
two bytes of packed BCD.

--BN

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

1997\11\11@145323 by gwaiche

picon face
Rick Dickinson wrote:
>
> I've seen quite a large number of postings by people looking for sonar devices
>  for robotics use.  The commonly suggested solution (the Polaroid sonar
module)
>  has several drawbacks, however: 1) it's expensive ($50 each or so), 2) it
needs
>  modifications to measure short distances, 3) the transducer used is fairly
>  large (1.25" or so diameter), and 4) your processor gets tied up calulating
the
>  range by timing the reflected chirp.
>
> Owing to the success of the various serial LCD "backpack"-type devices, I
>  thought it would be useful to develop a low-cost kit for an ultrasonic
ranging
>  unit, that could be accessed using some simple serial protocol.  I envision
>  this "Serial Sonar Unit" (SSU) being a small PIC-based PC board, with
>  connections to a pair of Murata 40 KHz transducers like the ones sold by All
>  Electronics for $2.50 a pair.
>
> The SSU would have two modes: continuous reading, and on-command.  If set to
>  continuous mode, the SSU would continually send out, and time the echos of,
>  tone bursts, storing the most recent result internally.  When polled, it
would
>  return the most recent reading.  In on-command mode, the SSU would wait for a
>  "go" command of some sort, then send a pulse and time its return.  If polled
>  before the measurement was complete, it would return some sort of "busy"
>  indication.  If polled after the measurement was complete, it would return
the
>  measurement.
>
> My intent is to come up with a design that will save my fellow hobbyists some
>  time and money, and will make it easy to incorporate sonar ranging into PIC
and
>  other small microcontroller-based projects.  Offloading the timing,
transducer
>  drive, and calculation tasks to a dedicated SSU will allow the programmer to
>  concentrate on the tasks to be done, not the ranging implementation.
Allowing
>  single-shot or continuous ranging will allow simpler implementations to use
the
{Quote hidden}

that
>  the discussion would be most valuable if everyone could participate, so
please
>  send replies to the PICLIST instead of directly to me.
>
> Thanks in advance,
>
>  - Rick Dickinson

Such a product already exist, and the cherry on top of the cake is
that it's pic based! (a basic stamp chip) It's called RadStamp, has a
range of 0.5 to 12m with a resolution of +/-10mm. The US sensor is
mounted on a stepper motor to make measures on 360 degrees. The device
has a RS232 output. It costs around 60$ but you need to add a Basic
Stamp2 to make it work. I guess it should be possible to replace the
BS2 with a "Pure" PIC chip.

It's distributed in UK by Milford Instruments.

Anyway, it will be fun to develop such a device by ourselves!

Cheers

Gael

1997\11\11@164711 by Rick Dickinson

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At 03:08 PM 11/11/97 -0500, TakeThisOuTkotayEraseMEspamspam_OUTahwanee.cs.dartmouth.edu wrote:

>As I wrote the stuff below I realized that the biggest
>decision you have to make is whether to design this
>product to interface to microprocessors or to
>computers.  If you design for microprocessors, some
>type of synchronous serial protocol is better and I
>would probably send the data in binary.  If you
>design for computers, an async serial protocol would
>be better and I would send the data in ASCII.

By breaking out the Communications Unit from the Ranging Unit, I should be able
to accommodate either one.

>>   -  Data format for measurement data returned

>I would suggest millimeters.

I suppose this would have to vary depending on the range being measured.

>>   -  I2C, SPI, or none of the above

>RS-485?  People may want to connect this to a PC which
>is why I might favor an async serial method.  It's
>easy to make an RS-232 to RS-485 converter and RS-485
>allows up to 32 nodes on a single twisted pair.

I was thinking it would make sense to leave the output at TTL levels, and allow
the end user to interface this to whatever physical medium was appropriate for
their application.

>>   -  Baud rate/clocking (async 9600/4800/2400/1200? Autobaud? Sync?)

>Async 9600.  You shouldn't need anything faster than that.

Agreed.... Not much data to send, so 9600 is overkill.  However, it's also
fairly "standard", so it's probably a good choice.

>>   -  Distribution mechanism
>>        PIC code/Schematics/PCB layout on web for download?
>>        Preprogrammed PICs and etched PCBs for purchase?

>Both if possible.

Agreed.  Right now I am leaning towards a standardized circuit and PCB, with
different versions of the Ranging Unit (RU) and Communications Unit (CU) PIC
code on a web site for download.  This way, we could pool resources to have a
batch of PCBs made up by a board fabrication house, and allow individuals to
program their own PICs.  I would also be willing to program PICs based on the
user's choice of the to-be-determined "standard" RU and CU designs.

- Rick "I love it when a plan comes together" Dickinson

+--------------------------------+------------------------------+
| Rick "The Notes Guy" Dickinson | Views expressed by the author|
| Lotus Notes & Domino Solutions | are not necessarily those of |
| (818)563-1061 RemoveMErtdspamTakeThisOuTnotesguy.com | Enterprise ArchiTechs.  They |
|   http://www.eArchiTechs.com   | might not even be mine....   |
+--------------------------------+------------------------------+

1997\11\11@193813 by Ross McKenzie

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At 09:30 AM 11/11/97 -0800, Rick "So many details to mail down" Dickinson wrote:

>What sort of granularity would you need in the measurement?  In other
words, how
> big of a "step size" is needed between readings?
>

Granularity? Are you thinking of "resolution" .... Expressed as 8, 12, 16,
whatever bit resolution. The "step size" is then a function of the range and
resolution of measurement.

Regards,

Ross McKenzie
Melbourne Australia

1997\11\11@202832 by Rick Dickinson

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At 11:34 AM 11/12/97 +1100, Ross McKenzie wrote:
>At 09:30 AM 11/11/97 -0800, Rick "So many details to mail down" Dickinson
wrote:
>
>>What sort of granularity would you need in the measurement?  In other
>words, how
>> big of a "step size" is needed between readings?
>>
>
>Granularity? Are you thinking of "resolution" .... Expressed as 8, 12, 16,
>whatever bit resolution. The "step size" is then a function of the range and
>resolution of measurement.

Exactly, Ross.  With, for instance, a conveniently chosen 21'4" range, an 8-bit
resolution will give you a granularity (or step size) of one inch.

I guess what I really meant to ask is "Am I correct in assuming that 8 bits of
resolution will be more than sufficient?".  It seems to me that, scaled over an
appropriate range, 8 bits would be appropriate for most hobbyist applications.

- Rick "Makes the circuit much easier, too" Dickinson

---
You can help design a Serial Sonar Unit for model robots!
 Vist http://www.notesguy.com/notesguy for details, or
  send mail to Rick Dickinson at rtdEraseMEspam.....notesguy.com

1997\11\11@204937 by Mike Keitz

picon face
On Tue, 11 Nov 1997 10:29:42 -0800 Rick Dickinson <EraseMErtdspamNOTESGUY.COM>
writes:
>At 01:33 PM 11/11/97 +0100, Alessandro Zummo wrote:
>>Il 11-Nov-97, Rick Dickinson scrisse:
>>
>[snip proposal for SSU]

>What sort of granularity would be needed,

The speed of sound in air varies with pressure, temperature, and
humidity.  Unless these factors are compensated for, granularity in the
measurement finer than the uncertainty of knowing the speed of sound is
not very useful.  In most applications, an absolute result is desired.

> and what is a reasonable
>maximum
> range?

The maximum range is whatever the transducers, transmitter, and receiver
allow.  For the Polaroid system it's about 30 feet.  This was well
matched for the original application of focusing a camera.   The parts in
the Polaroid circuit are rather high-performance (200V pulse to
transducer, stepped gain amplifier).  I don't know if the Murata
transducers could do better.

I want to avoid having to do any sort of AGC, so the range
>would have
> to be known in advance to set the amp gain on the receiving
>transducer.

This would really detract from the general-purpose utility of the device.
It shouldn't be hard to do AGC by using tri-state PIC pins to switch
resistors from various points in the receiver amplifier to ground.
Another way would be to vary the transmitter power. First try low power
assuming a short range, if no echo returns use high power and blank out
the spurious early returns.


>>>  -  Baud rate/clocking (async 9600/4800/2400/1200? Autobaud? Sync?)

I think async with a choice of 1200 or 9600 baud.  1200 could work better
if the device is at the end of long wires.  9600 would allow continuous
rapid measurements, or multiplexing the outputs of several units onto a
bus.  I like just sending ASCII text, since it allows making a quick
start with dumb-terminal software (or an actual dumb terminal).

If the unit does the conversion from time to distance, have a way to
input the local speed of sound.  There could also be a mode which just
outputs the time.
>
>I have been doing a little bit of design brainstorming, and have an
>idea or two
> about implementing the interface portion.

Really the form of the interface is the least of your worries.  If you
release the source code for the sonar core, then custom interfaces could
be developed as needed.

1997\11\11@215417 by Charles Hoss

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Alberto Smulders wrote:
>
> Hi Rick !!!
>
> Another very interested person here, looking for a cheap method to measure
> contents in grain and oil storage bins - should be a kind of ultrasonic
> rangefinder, maximum range around 10...12 meters, ruggedized for use in an
> industrial environment, some serial communication means for rather long
> distance (up to 1 km or so) if possible with unique address for
> interrogation, and.... (hmmm... am I asking too much ????)
>

no , not at all .
I make my on board car computer for my jeep and encountered the
same problem (noisy environment , lack of cables)
and came up with a simple idea (I guess I reinvented the wheel
but who cares) all units have serial numbers (one for the digi-compass
one for the dallas thermometer interface , one for fluid levels
and so on)
when the main system addresses one of them it wakes up (everybody else
goes sleepin') returns the required data and signs off with a 0ffh
the master waits for this (in case of timeout , displays the error)
the signoff is the reset for all the other systems .
now everybody waits for the next selector byte . and so on .

I guess this is not too complicated (most of the ideas came from the
dallas system , and biological analogs )

bye
charley

1997\11\11@224233 by Rick Dickinson

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At 02:11 PM 11/11/97 -0500, Mike Keitz wrote:
>On Tue, 11 Nov 1997 10:29:42 -0800 Rick Dickinson <RemoveMErtdEraseMEspamEraseMENOTESGUY.COM>
>writes:
>>What sort of granularity would be needed,
>
>The speed of sound in air varies with pressure, temperature, and
>humidity.  Unless these factors are compensated for, granularity in the
>measurement finer than the uncertainty of knowing the speed of sound is
>not very useful.  In most applications, an absolute result is desired.

Very true.  For this, and other, reasons, I don't think it make sense to try for
more than 8 bits of resolution over whatever range is being measured.  In fact,
for most hobbyist robotics applications, exact distance values aren't nearly as
useful as just being able to guage what fraction of the distance to something
you've already moved, so you can estimate how much longer to keep moving.

{Quote hidden}

Good point.  I wanted to keep the design as simple as possible for two reasons
-- to keep costs down so that hobbyists could afford to build it, and to make
it as simple to build and get "up and running" as possible.  I am afraid that
AGC circuitry would complicate the design and require some "tweaking" to make
it work.

>>>>  -  Baud rate/clocking (async 9600/4800/2400/1200? Autobaud? Sync?)
>
>I think async with a choice of 1200 or 9600 baud.  1200 could work better
>if the device is at the end of long wires.  9600 would allow continuous
>rapid measurements, or multiplexing the outputs of several units onto a
>bus.  I like just sending ASCII text, since it allows making a quick
>start with dumb-terminal software (or an actual dumb terminal).

True.  I'm planning on making the communication interface a separate unit from
the ranging unit.  This will allow a choice in output formats without
redesigning the whole thing.

>If the unit does the conversion from time to distance, have a way to
>input the local speed of sound.  There could also be a mode which just
>outputs the time.

I was actually thinking that just outputting the time might be the best all
around.  Let the end user decide if it's worth the math overhead to do the
conversion to distance units.

- Rick
---
You can help design a Serial Sonar Unit for model robots!
 Vist http://www.notesguy.com/notesguy for details, or
  send mail to Rick Dickinson at RemoveMErtdspam_OUTspamKILLspamnotesguy.com

1997\11\12@095055 by Guy Farebrother

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I would also be very interested.

The features that I would find useful would be to generate an interrupt
(toggle a pin?) whenever something enters a defined field within the range
of the device. This would be 3 - 4 inches. If a hand (or whatever) came
closer than 4 inches the unit would indicate that with a pin change
(toggle). The interface (serial) could then be used to determine range. The
defined field should be programmable so that I could set it to 4 inches, 40
inches, or whatever the min and max. values for the interface are.

Please keep me informed of any developments for this product.

PS It would have to work to -40 degrees C.

Guy

1997\11\12@103338 by Roger Books

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Robert Nansel wrote:

> Data returned: Time Of Flight (TOF) to nearest half millisecond in binary.
> Second choice would be BCD. Use TOF instead of absolute distance because
> seconds are the same in MKS and Conventional units, and each node can scale
> this into desired range units if needed. Also, you can adjust for
> temperature & altitude effects more readily.

TOF makes a lot of sense, if you need to measure distance in something other
than air the measurement is more "intuitive".  I wouldn't bother with BCD
though, binary math is much easier to deal with IMO.

Roger

1997\11\12@155534 by Martin R. Green

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The only problem I can see with your idea is that grain silos are
often choked with grain dust (which, by the way, is HIGHLY explosive),
which might very well introduce severe measurement errors.  Also, I
question whether the reflection from the grain would be of sufficient
intensity to measure.  The ultrasonic pulse would probably be
stretched immensely during reflection too since the grain surface
would likely be porous enough that reflection would occur from
anywhere in the first inch or two of grain.

Of course, all this might be irrelevant, so try it anyway.

On Tue, 11 Nov 1997 01:57:06 -0400, Alberto Smulders
<RemoveMEinsadTakeThisOuTspamspamITACOM.COM.PY> wrote:

{Quote hidden}

Martin R. Green
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1997\11\13@134343 by Eric van Es

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Alberto Smulders wrote:

> Hi Rick !!!
>
> Another very interested person here, looking for a cheap method to measure
> contents in grain and oil storage bins - should be a kind of ultrasonic
> rangefinder, maximum range around 10...12 meters, ruggedized for use in an
> industrial environment, some serial communication means for rather long
> distance (up to 1 km or so) if possible with unique address for
> interrogation, and.... (hmmm... am I asking too much ????)

I don't thinks so Alberto.

There are commercial unit available in SA. At work I had one that was for
industrial (mining) use. Range was more than 30metres (me tinks). Output was
industry standard 4-20mA output. Get one. Run 4-20mA through a resistor and
measure with a ADC & PIC. Transmit via one of many serial protocolli.....

Cheers!

--
Eric van Es               | Cape Town, South Africa
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1997\11\13@150422 by Alberto Smulders

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Eric van Es wrote:

> I don't thinks so Alberto.
>
> There are commercial unit available in SA. At work I had one that was for
> industrial (mining) use. Range was more than 30metres (me tinks). Output
was
> industry standard 4-20mA output. Get one. Run 4-20mA through a resistor
and
> measure with a ADC & PIC. Transmit via one of many serial protocolli.....
>
> Cheers!
>

Yes, I know there are commercial units available (see Cole Parmers
Catalogue), but their prices are prohibitive - and - as an example, now we
have a project here were we need about 28 level sensors (in the same
factory !). We even have projects sleeping because of the absolute
prohibitive cost of commercial available ultrasonic level sensors, so our
interest in developing our own - the technology involved mustn't be so
difficult!
By the way, I'm interested too in schematics - if possible in JPG format.

Regards,

Alberto Smulders
InSAD - Encarnacion, Paraguay
spamBeGoneinsadSTOPspamspamEraseMEitacom.com.py

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