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'Visiting ultrasonics, again...'
1996\03\25@095803 by Harrison Cooper

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Well, since the ultrasonic sensor I am trying to build it
interfaced to a PIC, its legal to talk about it here, right?

OK, I tried a couple of different circuits.  To generate the
40KHz signal, I brute forced it with a 40Kc xtal and a 4049.
That works fine, good square wave driving (and I can hear it).
Rx circuit, not so good.  I tried a couple of ways, but in one
case my amp turned into a osc (of course), and the other works
better (using a 324 quad amp), but the final stages seem dead.
Tried the obvious (new amp, etc), but it doesn't appear sensitive
enough.  I going to get another good analog guy to sit down and
see what he can tell me, but just curious what (if any) circuits
are proven to work.  Even an inexpensive commercial solution is
an option now (need to have this thing done by mid-april).  I
need to have a sense distance of 4 to 6 feet. Comments anyone ?

-Harrison Cooper
spam_OUThcooperTakeThisOuTspames.com

1996\03\25@125901 by Michael S. Hagberg

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>Well, since the ultrasonic sensor I am trying to build it
>interfaced to a PIC, its legal to talk about it here, right?
>
delete message

>-Harrison Cooper
> .....hcooperKILLspamspam@spam@es.com
>

Download microchip's app note AN597 Implementing Ultrasonic Ranging.

this interface requires ONLY 3 pins to connect to the polaroid 6500 module.
source code is included in the app note.

michael

1996\03\25@131145 by Bill Cornutt

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----------
>Well, since the ultrasonic sensor I am trying to build it
>interfaced to a PIC, its legal to talk about it here, right?
>
>OK, I tried a couple of different circuits.  To generate the
>40KHz signal, I brute forced it with a 40Kc xtal and a 4049.
>That works fine, good square wave driving (and I can hear it).
>Rx circuit, not so good.  I tried a couple of ways, but in one
>case my amp turned into a osc (of course), and the other works
>better (using a 324 quad amp), but the final stages seem dead.
>Tried the obvious (new amp, etc), but it doesn't appear sensitive
>enough.  I going to get another good analog guy to sit down and
>see what he can tell me, but just curious what (if any) circuits
>are proven to work.  Even an inexpensive commercial solution is
>an option now (need to have this thing done by mid-april).  I
>need to have a sense distance of 4 to 6 feet. Comments anyone ?
>
>-Harrison Cooper
> hcooperspamKILLspames.com
>

Might be that the xducers arn't the same or arn't centered at 40kc's.
(never expected to use the term kc again!)

Try swapping the xmitter and rec xducers.

If that don't work then try a varable osc like a
555 and adjust xmit frequencw until the receiver peeks.

If you are using the same xsucer for both xmit and receive then
adjust xmit frequency until receiver peeks.  And if you are
using one xducer, how do you get it to stop osilatting when time
to receive without residual oscilations?

Bill C.

1996\03\25@154157 by Mike Keitz

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{Quote hidden}

An internally-compensated general-purpose opamp like the 324 is generally
not suitable for 40 KHz signals, except maybe near unity gain (even then it
may not have the slew rate).  Try using a high-frequency op-amp like a 318
(or one of the many newer ones), a bipolar transistor amplifier, IF
amplifier chip (MC1330 ?) or maybe even a string of CMOS inverter sections
biased for linear operation.
Also, the Kapton film transdusers as used by Polaroid work similar to
condenser microphones:  they require a bias of a couple hundred volts DC.
In an echo-ranging system, the transducer is charged up with bias by
rectifying the transmit pulse so it is biased during the receive phase that
immediately follows.  Some provision for this would have to be made in a
split transducer system which I think is what you are trying.  Most likely
the piezoelectric types of transducer don't require bias.

-Mike

1996\03\25@233244 by terogers

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Harrison Cooper wrote:
>
> Well, since the ultrasonic sensor I am trying to build it
> interfaced to a PIC, its legal to talk about it here, right?
>
> OK, I tried a couple of different circuits.  To generate the

(more stuff here..)

You could try to get your analog guy to sit down and look at what's in
the Polaroid unit. Don't make any rash assumptions - it's like the
comments found buried in the SS system legacy code ('Subtle!'). I can't
really tell you what to do (what I've done belongs to Time Tech) but I
can tell you that just 'cause it's simple doesn't mean it's easy. If you
look at it right you'll get what you want.

Tom Rogers VP - R&D Time Tech, Inc.

1996\03\26@151149 by Moritz von Buttlar

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Hi !


I'm also currently working on an ultrasonic receiver.

>
> OK, I tried a couple of different circuits.  To generate the
> 40KHz signal, I brute forced it with a 40Kc xtal and a 4049.
> That works fine, good square wave driving (and I can hear it).
                                       ^^^^^^^^^^^^
                       How can you hear it if it's 40kHz ???
                       That's impossible...(or u are a bat)

> Rx circuit, not so good.  I tried a couple of ways, but in one
> case my amp turned into a osc (of course), and the other works
> better (using a 324 quad amp), but the final stages seem dead.
> Tried the obvious (new amp, etc), but it doesn't appear sensitive
> enough.  I going to get another good analog guy to sit down and


You should have at least an amplification of about 5000.
In order to get that at 40kHz it's often required to use a couple
of OPAMPS...Are you using a NE567 PLL tone decoder ? That's a
nice way for detecting the signal after it has been amplified.
Please tell me if you get some more information 'cause I also really
have to get my projekt done....


 ciao,

   Moritz





-----------------------
Moritz von Buttlar
Kiel, Northern Germany
+49-431-542834
## CrossPoint v3.02 ##

1996\03\28@093310 by Argiris A. Kranidiotis

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> of OPAMPS...Are you using a NE567 PLL tone decoder ? That's a
> nice way for detecting the signal after it has been amplified.
> Please tell me if you get some more information 'cause I also really
> have to get my projekt done....

My opinion is that a 567 (in order to be usefull) needs a long acquisition time.
This means you have to send several cycles of your ultrasonic signal, limiting
the distance you can detect (short ranges can't be detected). If you use a very
small capacitor, in order to get a fast responce from 567, then your tone
decoder will become useless with virtually no noise immunity.

I think simple threshold detection should be enough for your application.

Also, have in mind that a LM358 has a gain of about x10 at 40KHz ...!

It would be interesting to know how can we make an x5000 amplifier, without
of course getting EMI and all other kinds of noise (you know, aliens, UFO's
etc :-)

Best,

Argiris Kranidiotis.

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