Very Low Frequency Sine
Archiver
Posts: 46,084
I would appreciate any ideas as to how to generate a very low frequency sine
wave with a period of 3-5 minutes (or more) using a BS2.
wave with a period of 3-5 minutes (or more) using a BS2.
Comments
RTC chip (DS1302 springs to mind) you can output
varying voltages like this. The problem is to
'smooth' the output.
The BS2 can step from 0 to 255 and back in some
time period. The DtoA will convert the 0 to 255
into some stepped version of 0 to +5 volts.
It will look 'mostly' like a sign wave, will
actually be 255 'steps' between 0 and 5 volts.
You can add low-pass filtering to reduce the
'stepiness' of the output -- but at that low
a frequency, it could be difficult.
See the Parallax "Analog and Digital Course"
for more info.
Plus, why do you want to do this? The only
use I know of is a slow ramp needed for a
sound effect.
--- In basicstamps@yahoogroups.com, "eigenbraket" <mod@e...> wrote:
> I would appreciate any ideas as to how to generate a very low
frequency sine
> wave with a period of 3-5 minutes (or more) using a BS2.
>I would appreciate any ideas as to how to generate a very low frequency sine
>wave with a period of 3-5 minutes (or more) using a BS2.
What about connecting the Digital I/O's directly to an R2R (DAC) and then to
a Op-Amp configured as a voltage follower. Then it's just a matter of setting
the I/O pins to correspond to the correct analog level via a SIN/COS function,
or a pre-calculated lookup table.
things--exactly what I was thinking. I've given up on analog techniques.
Allan, to answer your question Why?--let's just say for the sake of ART.
Allan, you're right, the problem here is to smooth the output. The
"fundamental" being so low makes the partials low and very difficult to filter
with a low pass. I've done some research on low pass filters and the lowest
cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
activity). How to smooth the output of the DAC?!!!!
Matthew
gear-train driving a potentiometer. A "pot" has essentially infinite
resolution, and a gear train could convert a stepper running perhaps 60 RPM
down to the .01 Hz or so you need. Essentially, the gear train would
multiply the resolution of the stepper by its own ratio. Then just buffer to
suit.
Mike Sokol
mikes@m...
www.ModernRecording.com
"Yes, we're mum and dad - and good and bad -
and everyone's happy to be here.
Genesis-
Original Message
From: "eigenbraket" <mod@e...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, June 12, 2003 2:43 PM
Subject: [noparse][[/noparse]basicstamps] Very Low Frequency Sine
> Thank you Beau and Allan for your ideas. I think you're saying the same
> things--exactly what I was thinking. I've given up on analog techniques.
> Allan, to answer your question Why?--let's just say for the sake of ART.
> Allan, you're right, the problem here is to smooth the output. The
> "fundamental" being so low makes the partials low and very difficult to
filter
> with a low pass. I've done some research on low pass filters and the
lowest
> cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
> activity). How to smooth the output of the DAC?!!!!
> Matthew
>
>
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to me.
Matthew
--- In basicstamps@yahoogroups.com, "Mike Sokol" <mikes@m...> wrote:
> For such a low frequency, I would consider using a stepper motor through a
> gear-train driving a potentiometer. A "pot" has essentially infinite
> resolution, and a gear train could convert a stepper running perhaps 60
RPM
> down to the .01 Hz or so you need. Essentially, the gear train would
> multiply the resolution of the stepper by its own ratio. Then just buffer to
> suit.
>
> Mike Sokol
> mikes@m...
> www.ModernRecording.com
>
>
> "Yes, we're mum and dad - and good and bad -
> and everyone's happy to be here.
> Genesis-
>
>
Original Message
> To: <basicstamps@yahoogroups.com>
> Sent: Thursday, June 12, 2003 2:43 PM
> Subject: [noparse][[/noparse]basicstamps] Very Low Frequency Sine
>
>
> > Thank you Beau and Allan for your ideas. I think you're saying the same
> > things--exactly what I was thinking. I've given up on analog techniques.
> > Allan, to answer your question Why?--let's just say for the sake of ART.
> > Allan, you're right, the problem here is to smooth the output. The
> > "fundamental" being so low makes the partials low and very difficult to
> filter
> > with a low pass. I've done some research on low pass filters and the
> lowest
> > cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
> > activity). How to smooth the output of the DAC?!!!!
> > Matthew
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
> >
>things--exactly what I was thinking. I've given up on analog techniques.
>Allan, to answer your question Why?--let's just say for the sake of ART.
>Allan, you're right, the problem here is to smooth the output. The
>"fundamental" being so low makes the partials low and very difficult to filter
>with a low pass. I've done some research on low pass filters and the lowest
>cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
>activity). How to smooth the output of the DAC?!!!!
>Matthew
Start with a 16 bit D/A, then it will not need filtering that anyone
would notice. One bit at that level is like the thickness of one
sheet of paper in a stack 22 feet high. Or 12 bits, like one sheet
in a stack of 8 reams.
The TI TLV5618A is a dual 12-bit DAC in an 8-pin package, using
SHIFTOUT interface on the Stamp.
-- Tracy
(INTEGRATOR) so I don't know where you got the .01hz idea. First of all,
why do you need this great precision? The step distortion is relatively
insignificant at this frequency. A simple roll off filter will smooth the
edges of the steps from the dac and if this is not good enough, generate the
sine wave with analog circuitry that you could even phase lock to a high
frequency crystal time base for stability if frequency control is so
important.
Jim
http://www.geocities.com/jimforkin2003/
Original Message
From: eigenbraket [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=1kW_xUhmyqqlIgYgZEKw8tkembkM99mDlFGAUWjW-5ZTsnN3CSJun6HBAh3DAU632QuEMUjplQQ]mod@e...[/url
Sent: Thursday, June 12, 2003 2:43 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Very Low Frequency Sine
Thank you Beau and Allan for your ideas. I think you're saying the same
things--exactly what I was thinking. I've given up on analog techniques.
Allan, to answer your question Why?--let's just say for the sake of ART.
Allan, you're right, the problem here is to smooth the output. The
"fundamental" being so low makes the partials low and very difficult to
filter
with a low pass. I've done some research on low pass filters and the lowest
cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
activity). How to smooth the output of the DAC?!!!!
Matthew
To UNSUBSCRIBE, just send mail to:
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an op-amp low pass filter down to DC?
As far as analog techniques I've tried using the sine output of a couple
different function-generators-on-a-chip (XR2206 and 8038) without success.
The sine became grossly distored below 0.01 Hz. I've tried a relaxation
oscillator and that was stable but didn't produce a nice rounded sine, but
more of a triangle. Are you refering to some kind of a Wien bridge? As far as
stabilizing it with a PLL--this is beyond me right now. I do want a small range
of frequency control (1min-5min).
Matthew
--- In basicstamps@yahoogroups.com, "Jim Forkin" <jjf@p...> wrote:
> You can do low pass filtering down to dc with an op-amp low pass filter
> (INTEGRATOR) so I don't know where you got the .01hz idea. First of all,
> why do you need this great precision? The step distortion is relatively
> insignificant at this frequency. A simple roll off filter will smooth the
> edges of the steps from the dac and if this is not good enough, generate the
> sine wave with analog circuitry that you could even phase lock to a high
> frequency crystal time base for stability if frequency control is so
> important.
>
> Jim
> http://www.geocities.com/jimforkin2003/
>
>
>
Original Message
> From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> Sent: Thursday, June 12, 2003 2:43 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Very Low Frequency Sine
>
>
> Thank you Beau and Allan for your ideas. I think you're saying the same
> things--exactly what I was thinking. I've given up on analog techniques.
> Allan, to answer your question Why?--let's just say for the sake of ART.
> Allan, you're right, the problem here is to smooth the output. The
> "fundamental" being so low makes the partials low and very difficult to
> filter
> with a low pass. I've done some research on low pass filters and the lowest
> cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
> activity). How to smooth the output of the DAC?!!!!
> Matthew
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Define smooth...
amg
On Thu, 12 Jun 2003 18:43:17 -0000 "eigenbraket" <mod@e...>
writes:
> Thank you Beau and Allan for your ideas. I think you're saying the
> same
> things--exactly what I was thinking. I've given up on analog
> techniques.
> Allan, to answer your question Why?--let's just say for the sake of
> ART.
> Allan, you're right, the problem here is to smooth the output. The
>
> "fundamental" being so low makes the partials low and very difficult
> to filter
> with a low pass. I've done some research on low pass filters and
> the lowest
> cutoff frequency I've seen is around 0.01 Hz (for seismic and
> brainwave
> activity). How to smooth the output of the DAC?!!!!
> Matthew
________________________________________________________________
The best thing to hit the internet in years - Juno SpeedBand!
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12 bits over a period of 3min would mean a transition every 4 hundredths of a
second . . . uhm I guess that's pretty smooth!!
PS. I'm still curious about the analog solution using a low pass filter as this
was my first approach, but abandoned it.
--- In basicstamps@yahoogroups.com, amg amg <controlsdude2000@j...>
wrote:
> If you get a DAC with enough bits, do you really need to smooth it?
> Define smooth...
>
> amg
>
> On Thu, 12 Jun 2003 18:43:17 -0000 "eigenbraket" <mod@e...>
> writes:
> > Thank you Beau and Allan for your ideas. I think you're saying the
> > same
> > things--exactly what I was thinking. I've given up on analog
> > techniques.
> > Allan, to answer your question Why?--let's just say for the sake of
> > ART.
> > Allan, you're right, the problem here is to smooth the output. The
> >
> > "fundamental" being so low makes the partials low and very difficult
> > to filter
> > with a low pass. I've done some research on low pass filters and
> > the lowest
> > cutoff frequency I've seen is around 0.01 Hz (for seismic and
> > brainwave
> > activity). How to smooth the output of the DAC?!!!!
> > Matthew
>
>
____________________________________________________________
____
> The best thing to hit the internet in years - Juno SpeedBand!
> Surf the web up to FIVE TIMES FASTER!
> Only $14.95/ month - visit www.juno.com to sign up today!
occurs in reading words on a page or on a computer screen. Smooth eye
movements can occur while tracking a moving target at moderately low
frequencies, using an oculomotor brain system known as the smooth
pursuit system. It will not accurately track movements of any system
with a period of 3-5 minutes, but performs well at periods from about .1
to 1 seconds. So you need a better criterion than "imperceptible to the
human eye." Perception of motion is an even a higher-level problem
which supercedes objectively recorded "smooth" eye movements. So
perception of a transition of 4 hundredths of a second is not
physiologically possible.
I do research in human eye movements for fun and profit -- stamp related
of course [noparse]:)[/noparse] .
Dennis
Original Message
From: eigenbraket [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=1L_-ZysVlFjtDEqgUlanmrozcs1cYZbfbxTsMbWpHywBTXsEyb0YzlYhzqYG5CKCu7C7IgaH5j4]mod@e...[/url
Sent: Thursday, June 12, 2003 2:03 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
By "smooth" I mean imperceptible to the human eye.
12 bits over a period of 3min would mean a transition every 4 hundredths
of a
second . . . uhm I guess that's pretty smooth!!
PS. I'm still curious about the analog solution using a low pass filter
as this
was my first approach, but abandoned it.
--- In basicstamps@yahoogroups.com, amg amg <controlsdude2000@j...>
wrote:
> If you get a DAC with enough bits, do you really need to smooth it?
> Define smooth...
>
> amg
>
> On Thu, 12 Jun 2003 18:43:17 -0000 "eigenbraket" <mod@e...>
> writes:
> > Thank you Beau and Allan for your ideas. I think you're saying the
> > same
> > things--exactly what I was thinking. I've given up on analog
> > techniques.
> > Allan, to answer your question Why?--let's just say for the sake of
> > ART.
> > Allan, you're right, the problem here is to smooth the output. The
> >
> > "fundamental" being so low makes the partials low and very difficult
> > to filter
> > with a low pass. I've done some research on low pass filters and
> > the lowest
> > cutoff frequency I've seen is around 0.01 Hz (for seismic and
> > brainwave
> > activity). How to smooth the output of the DAC?!!!!
> > Matthew
>
>
____________________________________________________________
____
> The best thing to hit the internet in years - Juno SpeedBand! Surf the
> web up to FIVE TIMES FASTER! Only $14.95/ month - visit www.juno.com
> to sign up today!
To UNSUBSCRIBE, just send mail to:
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For circuits, look at any op-amp design text. Several were published by
National Semiconductor over the years and may be available on the internet.
Radio shack has some books on op amps and any college level electronics text
will help. Sounds like a trip to the local library is in order.
The American Radio Relay League has published several books which detail op
amp design including filters.
Here's an idea; use an op amp as an integrator with a slow response and
change the offset using a low level digital signal.
the output will track the input offset and will produce a sine wave.
Linearity may be difficult to achieve to a great extent, but at these
frequencies, you couldn't tell anyway.
jim
http://www.geocities.com/jimforkin2003/
Original Message
From: eigenbraket [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=b8AYLW0hzlqoGtSl10T25dL3hCsj1sPoyHE4Gq-4z0NbbxYB_GnGMU50WQomwng6Tjd-ppiozZZL5HNm]mod@e...[/url
Sent: Thursday, June 12, 2003 4:36 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
Thanks Jim for your comments. Could you direct me to some schematics of
an op-amp low pass filter down to DC?
As far as analog techniques I've tried using the sine output of a couple
different function-generators-on-a-chip (XR2206 and 8038) without success.
The sine became grossly distored below 0.01 Hz. I've tried a relaxation
oscillator and that was stable but didn't produce a nice rounded sine, but
more of a triangle. Are you refering to some kind of a Wien bridge? As far
as
stabilizing it with a PLL--this is beyond me right now. I do want a small
range
of frequency control (1min-5min).
Matthew
--- In basicstamps@yahoogroups.com, "Jim Forkin" <jjf@p...> wrote:
> You can do low pass filtering down to dc with an op-amp low pass filter
> (INTEGRATOR) so I don't know where you got the .01hz idea. First of all,
> why do you need this great precision? The step distortion is relatively
> insignificant at this frequency. A simple roll off filter will smooth the
> edges of the steps from the dac and if this is not good enough, generate
the
> sine wave with analog circuitry that you could even phase lock to a high
> frequency crystal time base for stability if frequency control is so
> important.
>
> Jim
> http://www.geocities.com/jimforkin2003/
>
>
>
Original Message
> From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> Sent: Thursday, June 12, 2003 2:43 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Very Low Frequency Sine
>
>
> Thank you Beau and Allan for your ideas. I think you're saying the same
> things--exactly what I was thinking. I've given up on analog techniques.
> Allan, to answer your question Why?--let's just say for the sake of ART.
> Allan, you're right, the problem here is to smooth the output. The
> "fundamental" being so low makes the partials low and very difficult to
> filter
> with a low pass. I've done some research on low pass filters and the
lowest
> cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
> activity). How to smooth the output of the DAC?!!!!
> Matthew
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
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get the stamp to move something that slowly.
Moving it in little 'jerks' is what the stamp is
going to do if you output a voltage change every
so often -- unless each 'jerk' is smoothed into
something slower than the criteria which
you've laid you here.
Personally, I can't directly watch the sweeping
of a minute hand and see it move -- but I can
observe it after a time and see it has moved.
That is, unless it is a 'digital' minute hand,
which steps from position to position. That
I can see.
--- In basicstamps@yahoogroups.com, Dennis O'Leary <doleary@e...>
wrote:
> The human eye generally moves in small jerks, called micro
saccades, as
> occurs in reading words on a page or on a computer screen. Smooth
eye
> movements can occur while tracking a moving target at moderately low
> frequencies, using an oculomotor brain system known as the smooth
> pursuit system. It will not accurately track movements of any
system
> with a period of 3-5 minutes, but performs well at periods from
about .1
> to 1 seconds. So you need a better criterion than "imperceptible
to the
> human eye." Perception of motion is an even a higher-level problem
> which supercedes objectively recorded "smooth" eye movements. So
> perception of a transition of 4 hundredths of a second is not
> physiologically possible.
>
> I do research in human eye movements for fun and profit -- stamp
related
> of course [noparse]:)[/noparse] .
>
> Dennis
>
>
Original Message
> From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> Sent: Thursday, June 12, 2003 2:03 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
>
>
> By "smooth" I mean imperceptible to the human eye.
> 12 bits over a period of 3min would mean a transition every 4
hundredths
> of a
> second . . . uhm I guess that's pretty smooth!!
>
> PS. I'm still curious about the analog solution using a low pass
filter
> as this
> was my first approach, but abandoned it.
>
>
>
>
> --- In basicstamps@yahoogroups.com, amg amg <controlsdude2000@j...>
> wrote:
> > If you get a DAC with enough bits, do you really need to smooth
it?
> > Define smooth...
> >
> > amg
> >
> > On Thu, 12 Jun 2003 18:43:17 -0000 "eigenbraket" <mod@e...>
> > writes:
> > > Thank you Beau and Allan for your ideas. I think you're saying
the
> > > same
> > > things--exactly what I was thinking. I've given up on analog
> > > techniques.
> > > Allan, to answer your question Why?--let's just say for the
sake of
> > > ART.
> > > Allan, you're right, the problem here is to smooth the output.
The
> > >
> > > "fundamental" being so low makes the partials low and very
difficult
> > > to filter
> > > with a low pass. I've done some research on low pass filters
and
> > > the lowest
> > > cutoff frequency I've seen is around 0.01 Hz (for seismic and
> > > brainwave
> > > activity). How to smooth the output of the DAC?!!!!
> > > Matthew
> >
> >
> ____________________________________________________________
> ____
> > The best thing to hit the internet in years - Juno SpeedBand!
Surf the
>
> > web up to FIVE TIMES FASTER! Only $14.95/ month - visit
www.juno.com
> > to sign up today!
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
Subject
> and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
the idea that whatever bit-resolution you decide to go
with, (be it an 8,10,12, or 16 bit DAC), and you ensure
that no more than 1 LSB changes on a clock transition. Then
shouldn't the only frequency that's required to be filtered
out is the fundamental frequency of the clock driving the
bits supplying the DAC?
Here is a table I generated indicating the required number
of steps between 0 and 360 deg with various bit-resolutions
guaranteeing that only 1 LSB changes on each clock transition
from a simple little QBASIC program that could be altered and
used to build a lookup table database.
res STEP (deg) steps/period
8-Bit 0.233 1,545
10-Bit 0.0568 6,338
12-Bit 0.01407 25,586
16-Bit 0.000875 411,428
'
'QBASIC program Start
'
CLS
Bits = 16
Pi = ATN(1) * 4
N = 2 ^ Bits
Count = 0
FOR Deg = 0 TO 360 STEP .000875
rad = (Deg / 180) * Pi
OldX = X
X = INT(SIN(rad) * N)
IF (X - OldX) > 1 THEN
PRINT Count, X, Deg
END IF
Count = Count + 1
NEXT Deg
PRINT "
"
PRINT Count, X, Deg
'
'QBASIC program End
'
3 min = 180 sec = 0.00555Hz
5 min = 300 sec = 0.00333Hz
...So the fundamental frequency for a 3 min Period @ 16_bit
resolution would be...
(.00555 x 411,428) = 2,283 Hz
...for a 5 min Period @ 16_bit this works out to...
(.00333 x 411,428) = 1,370 Hz
2,283Hz is what would be "audible" or considered noise on the
VLF output at 3Min and 1,370Hz at 5min
If your time interval changes or is adjustable as has been
indicated, then a simple LOW PASS filter set to at least twice
the highest fundamental you would be operating at.
-Beau Schwabe
>Good argument, but then his problem is how to
>get the stamp to move something that slowly.
>
>Moving it in little 'jerks' is what the stamp is
>going to do if you output a voltage change every
>so often -- unless each 'jerk' is smoothed into
>something slower than the criteria which
>you've laid you here.
>
>Personally, I can't directly watch the sweeping
>of a minute hand and see it move -- but I can
>observe it after a time and see it has moved.
>That is, unless it is a 'digital' minute hand,
>which steps from position to position. That
>I can see.
>
>--- In basicstamps@yahoogroups.com, Dennis O'Leary <doleary@e...>
>wrote:
> > The human eye generally moves in small jerks, called micro
>saccades, as
> > occurs in reading words on a page or on a computer screen. Smooth
>eye
> > movements can occur while tracking a moving target at moderately low
> > frequencies, using an oculomotor brain system known as the smooth
> > pursuit system. It will not accurately track movements of any
>system
> > with a period of 3-5 minutes, but performs well at periods from
>about .1
> > to 1 seconds. So you need a better criterion than "imperceptible
>to the
> > human eye." Perception of motion is an even a higher-level problem
> > which supercedes objectively recorded "smooth" eye movements. So
> > perception of a transition of 4 hundredths of a second is not
> > physiologically possible.
> >
> > I do research in human eye movements for fun and profit -- stamp
>related
> > of course [noparse]:)[/noparse] .
> >
> > Dennis
> >
> >
Original Message
> > From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> > Sent: Thursday, June 12, 2003 2:03 PM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
> >
> >
> > By "smooth" I mean imperceptible to the human eye.
> > 12 bits over a period of 3min would mean a transition every 4
>hundredths
> > of a
> > second . . . uhm I guess that's pretty smooth!!
> >
> > PS. I'm still curious about the analog solution using a low pass
>filter
> > as this
> > was my first approach, but abandoned it.
> >
> >
> >
> >
> > --- In basicstamps@yahoogroups.com, amg amg <controlsdude2000@j...>
> > wrote:
> > > If you get a DAC with enough bits, do you really need to smooth
>it?
> > > Define smooth...
> > >
> > > amg
> > >
> > > On Thu, 12 Jun 2003 18:43:17 -0000 "eigenbraket" <mod@e...>
> > > writes:
> > > > Thank you Beau and Allan for your ideas. I think you're saying
>the
> > > > same
> > > > things--exactly what I was thinking. I've given up on analog
> > > > techniques.
> > > > Allan, to answer your question Why?--let's just say for the
>sake of
> > > > ART.
> > > > Allan, you're right, the problem here is to smooth the output.
>The
> > > >
> > > > "fundamental" being so low makes the partials low and very
>difficult
> > > > to filter
> > > > with a low pass. I've done some research on low pass filters
>and
> > > > the lowest
> > > > cutoff frequency I've seen is around 0.01 Hz (for seismic and
> > > > brainwave
> > > > activity). How to smooth the output of the DAC?!!!!
> > > > Matthew
> > >
I poked around digikey's catalog and found some low pass filters in ic
packages available for less than $20.
5th order low pass from MAXIM (MAX281) "DC to 20kHz cutoff"
8th order low pass Linear Tech (LTC1064-3)
Matthew
--- In basicstamps@yahoogroups.com, "Jim Forkin" <jjf@p...> wrote:
> If you run a triangle wave through a low pass filter, you get a sine wave.
> For circuits, look at any op-amp design text. Several were published by
> National Semiconductor over the years and may be available on the
internet.
> Radio shack has some books on op amps and any college level electronics
text
> will help. Sounds like a trip to the local library is in order.
>
> The American Radio Relay League has published several books which
detail op
> amp design including filters.
>
> Here's an idea; use an op amp as an integrator with a slow response and
> change the offset using a low level digital signal.
> the output will track the input offset and will produce a sine wave.
> Linearity may be difficult to achieve to a great extent, but at these
> frequencies, you couldn't tell anyway.
>
> jim
> http://www.geocities.com/jimforkin2003/
>
>
>
Original Message
> From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> Sent: Thursday, June 12, 2003 4:36 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
>
>
> Thanks Jim for your comments. Could you direct me to some schematics of
> an op-amp low pass filter down to DC?
>
> As far as analog techniques I've tried using the sine output of a couple
> different function-generators-on-a-chip (XR2206 and 8038) without
success.
> The sine became grossly distored below 0.01 Hz. I've tried a relaxation
> oscillator and that was stable but didn't produce a nice rounded sine, but
> more of a triangle. Are you refering to some kind of a Wien bridge? As far
> as
> stabilizing it with a PLL--this is beyond me right now. I do want a small
> range
> of frequency control (1min-5min).
>
> Matthew
>
>
> --- In basicstamps@yahoogroups.com, "Jim Forkin" <jjf@p...> wrote:
> > You can do low pass filtering down to dc with an op-amp low pass filter
> > (INTEGRATOR) so I don't know where you got the .01hz idea. First of all,
> > why do you need this great precision? The step distortion is relatively
> > insignificant at this frequency. A simple roll off filter will smooth the
> > edges of the steps from the dac and if this is not good enough, generate
> the
> > sine wave with analog circuitry that you could even phase lock to a high
> > frequency crystal time base for stability if frequency control is so
> > important.
> >
> > Jim
> > http://www.geocities.com/jimforkin2003/
> >
> >
> >
Original Message
> > From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> > Sent: Thursday, June 12, 2003 2:43 PM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] Very Low Frequency Sine
> >
> >
> > Thank you Beau and Allan for your ideas. I think you're saying the same
> > things--exactly what I was thinking. I've given up on analog techniques.
> > Allan, to answer your question Why?--let's just say for the sake of ART.
> > Allan, you're right, the problem here is to smooth the output. The
> > "fundamental" being so low makes the partials low and very difficult to
> > filter
> > with a low pass. I've done some research on low pass filters and the
> lowest
> > cutoff frequency I've seen is around 0.01 Hz (for seismic and brainwave
> > activity). How to smooth the output of the DAC?!!!!
> > Matthew
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject and
> > Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
I don't understand you yet, but if you're right my life is much easier off.
I don't understand the first table you made:
res step (deg) steps/period
8-Bit 0.233 1,545
10-Bit 0.0568 6,338
12-Bit 0.01407 25,586
16-Bit 0.000875 411,428
How are you getting the middle column? Let's look at 16 bit resolution.
2^16 = 65536 steps
360degrees/65536 steps = 0.00549 degrees/step
Do you own a copy of the CMOS Cookbook?
--- In basicstamps@yahoogroups.com, "Beau Schwabe" <bschwabe@a...>
wrote:
> Perhaps I'm a little dense here... If you design around
> the idea that whatever bit-resolution you decide to go
> with, (be it an 8,10,12, or 16 bit DAC), and you ensure
> that no more than 1 LSB changes on a clock transition. Then
> shouldn't the only frequency that's required to be filtered
> out is the fundamental frequency of the clock driving the
> bits supplying the DAC?
>
> Here is a table I generated indicating the required number
> of steps between 0 and 360 deg with various bit-resolutions
> guaranteeing that only 1 LSB changes on each clock transition
> from a simple little QBASIC program that could be altered and
> used to build a lookup table database.
>
> res STEP (deg) steps/period
> 8-Bit 0.233 1,545
> 10-Bit 0.0568 6,338
> 12-Bit 0.01407 25,586
> 16-Bit 0.000875 411,428
>
>
>
> '
> 'QBASIC program Start
> '
> CLS
> Bits = 16
> Pi = ATN(1) * 4
> N = 2 ^ Bits
> Count = 0
> FOR Deg = 0 TO 360 STEP .000875
> rad = (Deg / 180) * Pi
> OldX = X
> X = INT(SIN(rad) * N)
> IF (X - OldX) > 1 THEN
> PRINT Count, X, Deg
> END IF
> Count = Count + 1
> NEXT Deg
> PRINT "
"
> PRINT Count, X, Deg
> '
> 'QBASIC program End
> '
>
>
> 3 min = 180 sec = 0.00555Hz
> 5 min = 300 sec = 0.00333Hz
>
> ...So the fundamental frequency for a 3 min Period @ 16_bit
> resolution would be...
> (.00555 x 411,428) = 2,283 Hz
>
> ...for a 5 min Period @ 16_bit this works out to...
> (.00333 x 411,428) = 1,370 Hz
>
> 2,283Hz is what would be "audible" or considered noise on the
> VLF output at 3Min and 1,370Hz at 5min
>
> If your time interval changes or is adjustable as has been
> indicated, then a simple LOW PASS filter set to at least twice
> the highest fundamental you would be operating at.
>
> -Beau Schwabe
>
>
> >Good argument, but then his problem is how to
> >get the stamp to move something that slowly.
> >
> >Moving it in little 'jerks' is what the stamp is
> >going to do if you output a voltage change every
> >so often -- unless each 'jerk' is smoothed into
> >something slower than the criteria which
> >you've laid you here.
> >
> >Personally, I can't directly watch the sweeping
> >of a minute hand and see it move -- but I can
> >observe it after a time and see it has moved.
> >That is, unless it is a 'digital' minute hand,
> >which steps from position to position. That
> >I can see.
> >
> >--- In basicstamps@yahoogroups.com, Dennis O'Leary <doleary@e...>
> >wrote:
> > > The human eye generally moves in small jerks, called micro
> >saccades, as
> > > occurs in reading words on a page or on a computer screen. Smooth
> >eye
> > > movements can occur while tracking a moving target at moderately low
> > > frequencies, using an oculomotor brain system known as the smooth
> > > pursuit system. It will not accurately track movements of any
> >system
> > > with a period of 3-5 minutes, but performs well at periods from
> >about .1
> > > to 1 seconds. So you need a better criterion than "imperceptible
> >to the
> > > human eye." Perception of motion is an even a higher-level problem
> > > which supercedes objectively recorded "smooth" eye movements. So
> > > perception of a transition of 4 hundredths of a second is not
> > > physiologically possible.
> > >
> > > I do research in human eye movements for fun and profit -- stamp
> >related
> > > of course [noparse]:)[/noparse] .
> > >
> > > Dennis
> > >
> > >
Original Message
> > > From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> > > Sent: Thursday, June 12, 2003 2:03 PM
> > > To: basicstamps@yahoogroups.com
> > > Subject: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
> > >
> > >
> > > By "smooth" I mean imperceptible to the human eye.
> > > 12 bits over a period of 3min would mean a transition every 4
> >hundredths
> > > of a
> > > second . . . uhm I guess that's pretty smooth!!
> > >
> > > PS. I'm still curious about the analog solution using a low pass
> >filter
> > > as this
> > > was my first approach, but abandoned it.
> > >
> > >
> > >
> > >
> > > --- In basicstamps@yahoogroups.com, amg amg <
controlsdude2000@j...>
> > > wrote:
> > > > If you get a DAC with enough bits, do you really need to smooth
> >it?
> > > > Define smooth...
> > > >
> > > > amg
> > > >
> > > > On Thu, 12 Jun 2003 18:43:17 -0000 "eigenbraket" <mod@e...>
> > > > writes:
> > > > > Thank you Beau and Allan for your ideas. I think you're saying
> >the
> > > > > same
> > > > > things--exactly what I was thinking. I've given up on analog
> > > > > techniques.
> > > > > Allan, to answer your question Why?--let's just say for the
> >sake of
> > > > > ART.
> > > > > Allan, you're right, the problem here is to smooth the output.
> >The
> > > > >
> > > > > "fundamental" being so low makes the partials low and very
> >difficult
> > > > > to filter
> > > > > with a low pass. I've done some research on low pass filters
> >and
> > > > > the lowest
> > > > > cutoff frequency I've seen is around 0.01 Hz (for seismic and
> > > > > brainwave
> > > > > activity). How to smooth the output of the DAC?!!!!
> > > > > Matthew
> > > >
of something that is linear. A sine wave however is not linear. Certain
Areas under the curve experience expansion and contraction if you are
incrementing the degree value in fixed increments. In other words there will
be some cases where consecutive points on the sine wave during expansion will
be greater than 1/65536. What I am suggesting is that if you desire a 16-Bit
resolution, then the precision should be maintained under the curve in a
worst case scenario (during expansion) so that the maximum delta between
consecutive points during an expansion of the sine should not exceed 1/65536,
otherwise the precision of the sine will be lost. If you agree that it is
possible to visually adjust the period of a sine wave so that you can represent
both the top half and the bottom half of a circle then what I'm about to
explain
might make more sense. Initially the "middle column" was derived by trial
and error with the program I provided indicating that there was only 1/65536
difference between consecutive points. However this value can be calculated
more accurately by the following....
Pi = 3.14159265359
StepsPerPeriod = (2^Bits) * 2 * Pi
DegreeStep = 1 / ( StepsPerPeriod / 360 )
FundamentalFrequency = ( 1 / ( Min * 60 ) ) * StepsPerPeriod
...In this case it works out to 0.000874 compared to 0.000875 for the
DegreeStep.
The difference is a result of integer rounding and the precision in which
Pi was
carried out.
-Beau Schwabe
>Beau,
>
>I don't understand you yet, but if you're right my life is much easier off.
>I don't understand the first table you made:
>
>res step (deg) steps/period
> 8-Bit 0.233 1,545
>10-Bit 0.0568 6,338
>12-Bit 0.01407 25,586
>16-Bit 0.000875 411,428
>
>How are you getting the middle column? Let's look at 16 bit resolution.
>2^16 = 65536 steps
>360degrees/65536 steps = 0.00549 degrees/step
>
>Do you own a copy of the CMOS Cookbook?
>
>
>--- In basicstamps@yahoogroups.com, "Beau Schwabe" <bschwabe@a...>
>wrote:
> > Perhaps I'm a little dense here... If you design around
> > the idea that whatever bit-resolution you decide to go
> > with, (be it an 8,10,12, or 16 bit DAC), and you ensure
> > that no more than 1 LSB changes on a clock transition. Then
> > shouldn't the only frequency that's required to be filtered
> > out is the fundamental frequency of the clock driving the
> > bits supplying the DAC?
> >
> > Here is a table I generated indicating the required number
> > of steps between 0 and 360 deg with various bit-resolutions
> > guaranteeing that only 1 LSB changes on each clock transition
> > from a simple little QBASIC program that could be altered and
> > used to build a lookup table database.
> >
> > res STEP (deg) steps/period
> > 8-Bit 0.233 1,545
> > 10-Bit 0.0568 6,338
> > 12-Bit 0.01407 25,586
> > 16-Bit 0.000875 411,428
> >
> >
> >
> > '
> > 'QBASIC program Start
> > '
> > CLS
> > Bits = 16
> > Pi = ATN(1) * 4
> > N = 2 ^ Bits
> > Count = 0
> > FOR Deg = 0 TO 360 STEP .000875
> > rad = (Deg / 180) * Pi
> > OldX = X
> > X = INT(SIN(rad) * N)
> > IF (X - OldX) > 1 THEN
> > PRINT Count, X, Deg
> > END IF
> > Count = Count + 1
> > NEXT Deg
> > PRINT "
"
> > PRINT Count, X, Deg
> > '
> > 'QBASIC program End
> > '
> >
> >
> > 3 min = 180 sec = 0.00555Hz
> > 5 min = 300 sec = 0.00333Hz
> >
> > ...So the fundamental frequency for a 3 min Period @ 16_bit
> > resolution would be...
> > (.00555 x 411,428) = 2,283 Hz
> >
> > ...for a 5 min Period @ 16_bit this works out to...
> > (.00333 x 411,428) = 1,370 Hz
> >
> > 2,283Hz is what would be "audible" or considered noise on the
> > VLF output at 3Min and 1,370Hz at 5min
> >
> > If your time interval changes or is adjustable as has been
> > indicated, then a simple LOW PASS filter set to at least twice
> > the highest fundamental you would be operating at.
> >
> > -Beau Schwabe
> >
> >
> > >Good argument, but then his problem is how to
> > >get the stamp to move something that slowly.
> > >
> > >Moving it in little 'jerks' is what the stamp is
> > >going to do if you output a voltage change every
> > >so often -- unless each 'jerk' is smoothed into
> > >something slower than the criteria which
> > >you've laid you here.
> > >
> > >Personally, I can't directly watch the sweeping
> > >of a minute hand and see it move -- but I can
> > >observe it after a time and see it has moved.
> > >That is, unless it is a 'digital' minute hand,
> > >which steps from position to position. That
> > >I can see.
> > >
> > >--- In basicstamps@yahoogroups.com, Dennis O'Leary <doleary@e...>
> > >wrote:
> > > > The human eye generally moves in small jerks, called micro
> > >saccades, as
> > > > occurs in reading words on a page or on a computer screen. Smooth
> > >eye
> > > > movements can occur while tracking a moving target at moderately low
> > > > frequencies, using an oculomotor brain system known as the smooth
> > > > pursuit system. It will not accurately track movements of any
> > >system
> > > > with a period of 3-5 minutes, but performs well at periods from
> > >about .1
> > > > to 1 seconds. So you need a better criterion than "imperceptible
> > >to the
> > > > human eye." Perception of motion is an even a higher-level problem
> > > > which supercedes objectively recorded "smooth" eye movements. So
> > > > perception of a transition of 4 hundredths of a second is not
> > > > physiologically possible.
> > > >
> > > > I do research in human eye movements for fun and profit -- stamp
> > >related
> > > > of course [noparse]:)[/noparse] .
> > > >
> > > > Dennis
> > > >
> > > >
Original Message
> > > > From: eigenbraket [noparse][[/noparse]mailto:mod@e...]
> > > > Sent: Thursday, June 12, 2003 2:03 PM
> > > > To: basicstamps@yahoogroups.com
> > > > Subject: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
> > > >
> > > >
> > > > By "smooth" I mean imperceptible to the human eye.
> > > > 12 bits over a period of 3min would mean a transition every 4
> > >hundredths
> > > > of a
> > > > second . . . uhm I guess that's pretty smooth!!
> > > >
> > > > PS. I'm still curious about the analog solution using a low pass
> > >filter
> > > > as this
> > > > was my first approach, but abandoned it.
> > > >
> > > >
> > > >
> > > >
> > > > --- In basicstamps@yahoogroups.com, amg amg <
>controlsdude2000@j...>
> > > > wrote:
> > > > > If you get a DAC with enough bits, do you really need to smooth
> > >it?
> > > > > Define smooth...
> > > > >
> > > > > amg
> > > > >
> > > > > On Thu, 12 Jun 2003 18:43:17 -0000 "eigenbraket" <mod@e...>
> > > > > writes:
> > > > > > Thank you Beau and Allan for your ideas. I think you're saying
> > >the
> > > > > > same
> > > > > > things--exactly what I was thinking. I've given up on analog
> > > > > > techniques.
> > > > > > Allan, to answer your question Why?--let's just say for the
> > >sake of
> > > > > > ART.
> > > > > > Allan, you're right, the problem here is to smooth the output.
> > >The
> > > > > >
> > > > > > "fundamental" being so low makes the partials low and very
> > >difficult
> > > > > > to filter
> > > > > > with a low pass. I've done some research on low pass filters
> > >and
> > > > > > the lowest
> > > > > > cutoff frequency I've seen is around 0.01 Hz (for seismic and
> > > > > > brainwave
> > > > > > activity). How to smooth the output of the DAC?!!!!
> > > > > > Matthew
> > > > >
motor with a sinusoidal profile to create a laser-diode moving target
for a visual moving stimulus. At the peak of the sine wave, the
step-to-step amplitude change is so small that I just let the beam dwell
at the same amplitude for about 12 steps.
Dennis
Original Message
From: Beau Schwabe [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ijpxF2dS7IE3QaRHp-p-2H_pId6Q7-DP65bNl8PH530WT_IjxBBLZBgjyCcl2OlIc9gKjPiPgyvpBZ_Hbf24]bschwabe@a...[/url
Sent: Monday, June 16, 2003 8:11 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Re: Very Low Frequency Sine
Yes, 16 bit resolution is 65536 steps IF you are representing the
resolution of something that is linear. A sine wave however is not
linear. Certain Areas under the curve experience expansion and
contraction if you are incrementing the degree value in fixed
increments. In other words there will be some cases where consecutive
points on the sine wave during expansion will be greater than 1/65536.
What I am suggesting is that if you desire a 16-Bit resolution, then the
precision should be maintained under the curve in a worst case scenario
(during expansion) so that the maximum delta between consecutive points
during an expansion of the sine should not exceed 1/65536, otherwise the
precision of the sine will be lost. If you agree that it is possible to
visually adjust the period of a sine wave so that you can represent both
the top half and the bottom half of a circle then what I'm about to
explain
might make more sense. Initially the "middle column" was derived by
trial and error with the program I provided indicating that there was
only 1/65536 difference between consecutive points. However this value
can be calculated more accurately by the following....
Pi = 3.14159265359
StepsPerPeriod = (2^Bits) * 2 * Pi
DegreeStep = 1 / ( StepsPerPeriod / 360 )
FundamentalFrequency = ( 1 / ( Min * 60 ) ) * StepsPerPeriod
...In this case it works out to 0.000874 compared to 0.000875 for the
DegreeStep.
The difference is a result of integer rounding and the precision in
which
Pi was
carried out.
-Beau Schwabe