2sx & Sonic Rangefinding
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Posts: 46,084
I was curious to know if anyone has tried to use the sonic
rangefinding circuit found in the Basic Stamp I application notes
with the 2SX module. I seem to be having a problem getting any
accurate results. I have adapted the code from the Stamp I syntax
(Sonar.bas) to the 2SX, but my ultrasonic signal travel time
variable has random, bunk values.
I have hooked up my rangefinding circuit up to an o-scope, and the
circuit seems to be working find. The only thing I can think of
causing problems is that the output pin from the tone decoder (567)
fluctuates a little when the pin transistions from high to low when
it has detected an appropriate signal. Could the switching of the
signal from the tone decoder be the problem? Something a debouncing
switch would fix? Also, if the tone decoder oscillation frequency
is not completely in synch with the ultrasonic transmission signal,
would be a explanation for the incorrect values? The values tend to
stay in certain range and never change despite a change in the
distance from an obstable.
I have o-scope images of various stages of the sonic randfinding
circuit.
Thanks,
Warren
rangefinding circuit found in the Basic Stamp I application notes
with the 2SX module. I seem to be having a problem getting any
accurate results. I have adapted the code from the Stamp I syntax
(Sonar.bas) to the 2SX, but my ultrasonic signal travel time
variable has random, bunk values.
I have hooked up my rangefinding circuit up to an o-scope, and the
circuit seems to be working find. The only thing I can think of
causing problems is that the output pin from the tone decoder (567)
fluctuates a little when the pin transistions from high to low when
it has detected an appropriate signal. Could the switching of the
signal from the tone decoder be the problem? Something a debouncing
switch would fix? Also, if the tone decoder oscillation frequency
is not completely in synch with the ultrasonic transmission signal,
would be a explanation for the incorrect values? The values tend to
stay in certain range and never change despite a change in the
distance from an obstable.
I have o-scope images of various stages of the sonic randfinding
circuit.
Thanks,
Warren
Comments
Thanks for the input. I kind of already had done some of the things
that you suggested, and I still seem to be having trouble. My power
source was on a different board to start off with. The problem that
you have, do you know if that is an issue with the circuit or the
interface between your circuit and your microcontroller/processor?
What stamp are you using, by the way?
This problem has been plaguing me for quite some time now. Any
input, suggestions, or resources would be greatly appreciated.
Thanks,
Warren
--- In basicstamps@y..., "ulibasic" <ulibasic@r...> wrote:
> Hi Warren,
>
> just a general advice: when working with sonar / ultrasonic stuff
you
> sometimes get the impression that your place is haunted because
that stuff
> is so deliberately sensitive to any kind of noise and all..
> Have been working on a similar problem for two days now, strange
> measurements, random behaviour and the last thing I did was I cut
the board
> in two, seperating the power supply from the rest of the circuit.
Now if I
> put it some 5 inch away from each other it works perfect!!! Donot
really
> know why but you never do with sonar stuff...
>
> Good luck, Uli
>
>
>
>
Urspr
Thanks for the input. I kind of already had done some of the things
that you suggested, and I still seem to be having trouble. My power
source was on a different board to start off with. The problem that
you have, do you know if that is an issue with the circuit or the
interface between your circuit and your microcontroller/processor?
What stamp are you using, by the way?
This problem has been plaguing me for quite some time now. Any
input, suggestions, or resources would be greatly appreciated.
Thanks,
Warren
--- In basicstamps@y..., "ulibasic" <ulibasic@r...> wrote:
> Hi Warren,
>
> just a general advice: when working with sonar / ultrasonic stuff
you
> sometimes get the impression that your place is haunted because
that stuff
> is so deliberately sensitive to any kind of noise and all..
> Have been working on a similar problem for two days now, strange
> measurements, random behaviour and the last thing I did was I cut
the board
> in two, seperating the power supply from the rest of the circuit.
Now if I
> put it some 5 inch away from each other it works perfect!!! Donot
really
> know why but you never do with sonar stuff...
>
> Good luck, Uli
>
>
>
>
Urspr
Are you *sure* you have got your timing right? I seem to recall a mention in
the app note about making sure that there is a reasonable timing gap between
the TX phase and the RX phase otherwise you get all sorts of spurious noise.
Also, check your power supply - is it man enough for the project?
Lastly look at your +vdd rail decoupling - it will do no harm to sprinkle a
few 10nf caramics across any and all rail eletrolytics - on both the TX and
RX side. Also think about putting a 10nf cap at the point where the PSU
wires connects to your project box or breadboard.
Regards,
Tony Wells
Original Message
From: "mauritian37" <mauritian37@h...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, January 14, 2002 6:42 PM
Subject: [noparse][[/noparse]basicstamps] Re: 2sx & Sonic Rangefinding
Uli,
Thanks for the input. I kind of already had done some of the things
that you suggested, and I still seem to be having trouble. My power
source was on a different board to start off with. The problem that
you have, do you know if that is an issue with the circuit or the
interface between your circuit and your microcontroller/processor?
What stamp are you using, by the way?
This problem has been plaguing me for quite some time now. Any
input, suggestions, or resources would be greatly appreciated.
Thanks,
Warren
--- In basicstamps@y..., "ulibasic" <ulibasic@r...> wrote:
> Hi Warren,
>
> just a general advice: when working with sonar / ultrasonic stuff
you
> sometimes get the impression that your place is haunted because
that stuff
> is so deliberately sensitive to any kind of noise and all..
> Have been working on a similar problem for two days now, strange
> measurements, random behaviour and the last thing I did was I cut
the board
> in two, seperating the power supply from the rest of the circuit.
Now if I
> put it some 5 inch away from each other it works perfect!!! Donot
really
> know why but you never do with sonar stuff...
>
> Good luck, Uli
>
>
>
>
Urspr
Most electrolytics don't have any effect as ripple reducers and transient
smoothers at frequencies above 40Khz upwards. So an electrolytic across a
supply rail on something running at 40Khz or above is probably about as much
use as a cholocate teapot. They still work fine for low-frequency ripples,
but not the higher frequency smoothing.
The favorite trick for radio requency designers who see this problem all the
time, is to use low-value non-electrolytic capacitors across eletrolytics in
important places. You tend to use a capacitance to suit the frequency
involved. Memory of similar 40Khz circuits tells me that 10nF worked quite
well for me. At 40Khz it doesn't matter what the type is, I suppose, just
use whatever is in your junk box.
Regards,
Tony
Original Message
From: "ulibasic" <ulibasic@r...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, January 15, 2002 7:33 AM
Subject: AW: [noparse][[/noparse]basicstamps] Re: 2sx & Sonic Rangefinding
Hey Tony,
good idea to check the power supply for sufficient ampere, sorry Warren I
forgot this important point.
Tony, could you describe that part about the decoupling and the caps a
little more? seems there is something to learn for me there...
Thanks, Uli
Urspr
Most electrolytics don't have any effect as ripple reducers and transient
smoothers at frequencies above 40Khz upwards. So an electrolytic across a
supply rail on something running at 40Khz or above is probably about as much
use as a cholocate teapot. They still work fine for low-frequency ripples,
but not the higher frequency smoothing.
The favorite trick for radio requency designers who see this problem all the
time, is to use low-value non-electrolytic capacitors across eletrolytics in
important places. You tend to use a capacitance to suit the frequency
involved. Memory of similar 40Khz circuits tells me that 10nF worked quite
well for me. At 40Khz it doesn't matter what the type is, I suppose, just
use whatever is in your junk box.
Regards,
Tony
Original Message
From: "ulibasic" <ulibasic@r...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, January 15, 2002 7:33 AM
Subject: AW: [noparse][[/noparse]basicstamps] Re: 2sx & Sonic Rangefinding
Hey Tony,
good idea to check the power supply for sufficient ampere, sorry Warren I
forgot this important point.
Tony, could you describe that part about the decoupling and the caps a
little more? seems there is something to learn for me there...
Thanks, Uli
Urspr
camera, the kind with ultrasonic autofocus.
Look for the ones with the 1-1 1/2" dia. circle on the front with the metal
grid over it--that's the ultrasonic autofocus thingy. They work extremely
well--fast & accurate, and disassembling one might provide some clues as to
how Polaroid got it all to work so perfectly. I've thought about just
taking the asembly from one & integrating it into one of my projects, but
haven't got around to it yet...
Good luck.
lots of wires a nice mirror and some lenses
Original Message
From: "Ted Fines" <fines@m...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, January 16, 2002 9:10 AM
Subject: [noparse][[/noparse]basicstamps] Re: 2sx & Sonic Rangefinding
> You might want to go to a nearby thrift store and pick up an old Polaroid
> camera, the kind with ultrasonic autofocus.
>
> Look for the ones with the 1-1 1/2" dia. circle on the front with the
metal
> grid over it--that's the ultrasonic autofocus thingy. They work extremely
> well--fast & accurate, and disassembling one might provide some clues as
to
> how Polaroid got it all to work so perfectly. I've thought about just
> taking the asembly from one & integrating it into one of my projects, but
> haven't got around to it yet...
>
> Good luck.
>
>
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3000mAh, 7.2V RC car battery. I figured this should be enough for
my ultrasonics at least. In the future, I will be running other
components off the same battery (motors, circuitry), but for now,
all I am trying to do is power the microcontroller and the
ultrasonic circuit.
As far as the timing is concerned, I am following the code provided
in the application notes. The program calls for a 0.5 ms pulse from
the stamp to ensure that the decoder picks up the signal. What I am
thinking now is that there might be "chatter" from my tone decoder,
because maybe my receiver is not damping fast enough. I'm not sure
though. I have taken the steps to wrap a rubber band around the
receiver to account for this, but I don't know the damping
characteristics of my receiver to know for sure. Any suggestions?
I have some images from an o-scope that people can look at if they
are interested. What makes me concerned from the images that I have
is that there seems to be this "chatter" that I spoke of earlier. I
am not sure whether this is due to the receiver speaker, or possibly
an issue with +vdd rail decoupling. Tony, my experience with
electronics is somewhat limited. If you could go into more detail
on what you suggested, that would be great.
Thanks,
Warren
--- In basicstamps@y..., "ulibasic" <ulibasic@r...> wrote:
> Hey Tony,
>
> good idea to check the power supply for sufficient ampere, sorry
Warren I
> forgot this important point.
> Tony, could you describe that part about the decoupling and the
caps a
> little more? seems there is something to learn for me there...
>
>
> Thanks, Uli
>
>
>
>
Urspr