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'[EE] Fundamental frequency from a ...motor?'
2005\04\05@163611 by Barry Gershenfeld

face picon face
I had a (strange / PICList-suitable) idea last week, along similar lines,
so I guess this would be a good time to fling it out there.  Same basic
idea, but build an audio tachometer.

<ramble>

I was over on the embedinc site reading about the design of a circuit to
clean up the signal from "an innovative, patented magnetic sensor" and I
got to thinking about how things always look simple when you start, but
after reality sets in you usually are doing some fancy signal conditioning
to make the thing work.  And I thought about all the noise, harmonics, and
"stuff" that makes zero-crossing detectors seem to work until you
demonstrate them to the customer, wherein they (the sensors, not the
customers) take this as a cue to go whacko and it's back to the drawing
board.   So then I thought about FFT's and signal processors, and how
that's a brute-force approach but it ought to at least work well.  Just
imagine the waveform you'd get if you put a microphone in the vicinity of a
running engine.  Now think about how you can work the gearshift of your car
without a tachometer.  Your ears are pretty good at "hearing" the engine
RPM  (your brain, actually).

Many years ago there was such a beast called an "optical mouse".  This was
a pointing device with no ball but rather some optical pickups and a
special "mouse pad" with a grid printed on it.  These things worked OK (not
perfect) but you had to use that grid.  If you tried it on, say, a printed
page it would move the cursor but it was very nutty.   So, I thought, all
you have to do it mount a tiny camera in there and then figure out which
way the "picture" moved.  Now, that, in theory, could work, but it was such
an outrageously complex and expensive idea that I generally told this only
as a joke.

You know the rest...a couple of years ago a co-worker showed me this new
"optical mouse" that Microsoft was making.  I remember "it had as much CPU
power as a 386" and stuff like that.  And you can buy them for less than
$50 now.  And no one gives it a second thought.

So I'm thinking, dsPIC and all that.  Though, in the thread that preceded
this, you almost have me convinced we wouldn't need to do all this.  Still,
think about that mouse.  It works on (almost) any surface.  The tach would
work with (almost) any motor.

</ramble>

Barry


2005\04\05@165514 by Carey Fisher - NCS

face picon face

  > You know the rest...a couple of years ago a co-worker showed
  > me this new
  > "optical mouse" that Microsoft was making.  I remember "it had
  > as much CPU
  > power as a 386" and stuff like that.  And you can buy them for
  > less than
  > $50 now.  And no one gives it a second thought.
  >
 Just how do optical mice (mouses?, meece?) work?
Carey Fisher

2005\04\05@171455 by Josh Koffman

face picon face
Essentially they take many high speed pictures of the surface you're
mousing on. The sideways shining light highlights irregularities in
the surface, and the camera compares each capture to the earlier one,
determining which way you've moved the mouse.

Hope that's clear enough :)

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

On Apr 5, 2005 4:55 PM, Carey Fisher - NCS <spam_OUTcareyfisherTakeThisOuTspamncsradio.com> wrote:
>   Just how do optical mice (mouses?, meece?) work?

2005\04\05@174224 by Danny Decell

picon face

>  Just how do optical mice (mouses?, meece?) work?
> Carey Fisher

Here is one way to put it .. hehe  ... Tiny little digital camera takes
pictures of patterns under the mouse then does DSP analysis on each of the
images at 18 mips to see if the patterns changed :) *I'm still laughing I
can't help it*

http://computer.howstuffworks.com/question631.htm

Here is another way (bottom of page) ..  two light sensors / axis that get
interrupted as the mouse moves forming a couple of clock signals that allow
you to decode four discrete bit pairs to tell what direction you are going

http://users.tkk.fi/~then/mytexts/mouse.html

In all seriousness,  the last Microsoft optical mouse I ripped apart (few
years ago)  had a PIC (16C54 if my memory serves me right) counting those
pulses :)

- Dan


2005\04\05@174941 by Spehro Pefhany

picon face
At 04:55 PM 4/5/2005 -0400, you wrote:

>    > You know the rest...a couple of years ago a co-worker showed
>    > me this new
>    > "optical mouse" that Microsoft was making.  I remember "it had
>    > as much CPU
>    > power as a 386" and stuff like that.  And you can buy them for
>    > less than
>    > $50 now.  And no one gives it a second thought.
>    >
>   Just how do optical mice (mouses?, meece?) work?
>Carey Fisher

Here's a data sheet for one of the many sensor/processor chips used:
http://cp.literature.agilent.com/litweb/pdf/5989-1401EN.pdf

They have progressed from 1500 frames per second in the original Agilent
chip to 6000 frames per second in more recent ST chips used in the
current version of the MS IntelliMouse.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2005\04\05@180256 by Bradley Ferguson

picon face
On Apr 5, 2005 4:42 PM, Danny Decell <d.decellspamKILLspamcomcast.net> wrote:
{Quote hidden}

Just to point out, your second link refers to a "regular" mouse that
uses an (rotary) optical encoder--not what we refer to as an optical
mouse nowadays.  It is easy to count the quadrature signal from the
pairs of encoders with a PIC or with a one of the special ICs
available.

I have to imagine that they use some good math tricks to correlate the
images picked up by a "modern" optical mouse.  I would assume that
there are some papers on this somewhere unless everyone is buying the
same IP for the range of optical mice available.

At home I use a Logitech Dual Optical, which has two LEDs and two
sensors placed apart and 45 degrees to one another.  This mouse has
never suffered from the stutter or jumpiness that you might find with
other optical mice.  Too bad they discontinued it.  Does anyone know
about the newer one that makes claims of a laser?  I have to think
that there is no laser involved and that it is just a name given to
the mouse.

Bradley
(Someone should change the subject if this thread is going to continue...)

2005\04\05@182903 by Stef Mientki

flavicon
face
and here are some pictures taken from an optical mouse,
a 16F876 is sending the information to the PC.

http://oase.uci.kun.nl/~mientki/pic/projects/optical_mouse/optical_mouse.html

Stef Mientki

>

2005\04\05@215508 by Bob Ammerman

picon face
> Here is another way (bottom of page) ..  two light sensors / axis that get
> interrupted as the mouse moves forming a couple of clock signals that
> allow you to decode four discrete bit pairs to tell what direction you are
> going
>
> http://users.tkk.fi/~then/mytexts/mouse.html
>
> In all seriousness,  the last Microsoft optical mouse I ripped apart (few
> years ago)  had a PIC (16C54 if my memory serves me right) counting those
> pulses :)
>
> - Dan
>

The above URL does _not_ describe an optical mouse and how it works. It
describes a conventional mouse.

Bob Ammerman
RAm Systems


2005\04\05@222605 by Glenn Jones

picon face
Such a mechanical device exists. I'm not sure what they're called, but
my grandpa who was a mechanic had this little round thing that was
magnetic. You stuck it to an engine and turned the dial until the
little steel piano wire vibrated some special way (probably so that
the tip was stationary) and then you could read the engine speed from
the dial. Not as fancy as an FFT but it seemed to work.

On Apr 5, 2005 1:36 PM, Barry Gershenfeld <.....barry_gKILLspamspam.....zmicro.com> wrote:
{Quote hidden}

> -

2005\04\06@044559 by Alan B. Pearce

face picon face
>Just imagine the waveform you'd get if you put a microphone in the
>vicinity of a running engine.  Now think about how you can work the
>gearshift of your car without a tachometer.  Your ears are pretty
>good at "hearing" the engine RPM  (your brain, actually).
...
>So I'm thinking, dsPIC and all that.  Though, in the thread that
>preceded this, you almost have me convinced we wouldn't need to do
>all this.  Still, think about that mouse.  It works on (almost) any
>surface.  The tach would work with (almost) any motor.

Someone once reckoned that using the sound from a racecar motor was how the
TV companies produced on-screen displays of rev counters. I suspect that
these days part of being in the sport requires providing such telemetry to
the broadcast companies, but early on they used the sound from the on-board
cameras. IIRC this was how they decided the early BMW F1 engines were
confirmed to be revving to 19k/min.

2005\04\06@102218 by Danny Decell

picon face
That was my goof sorry Bob :(

----- Original Message -----
From: "Bob Ammerman" <EraseMErammermanspam_OUTspamTakeThisOuTverizon.net>
To: "Microcontroller discussion list - Public." <piclistspamspam_OUTmit.edu>
Sent: Tuesday, April 05, 2005 9:51 PM
Subject: Re: [EE] Fundamental frequency from a ...motor?


{Quote hidden}

> --

2005\04\06@113506 by Bradley Ferguson

picon face
On Apr 6, 2005 3:45 AM, Alan B. Pearce <@spam@A.B.PearceKILLspamspamrl.ac.uk> wrote:
> >Just imagine the waveform you'd get if you put a microphone in the
> >vicinity of a running engine.  Now think about how you can work the
> >gearshift of your car without a tachometer.  Your ears are pretty
> >good at "hearing" the engine RPM  (your brain, actually).
> ...
> >So I'm thinking, dsPIC and all that.  Though, in the thread that
> >preceded this, you almost have me convinced we wouldn't need to do
> >all this.  Still, think about that mouse.  It works on (almost) any
> >surface.  The tach would work with (almost) any motor.
>
> Someone once reckoned that using the sound from a racecar motor was how the
> TV companies produced on-screen displays of rev counters. I suspect that
> these days part of being in the sport requires providing such telemetry to
> the broadcast companies, but early on they used the sound from the on-board
> cameras. IIRC this was how they decided the early BMW F1 engines were
> confirmed to be revving to 19k/min.

I imagine that would be quite effective.  Consider this link:
http://www.drewtaylor.com/asiatech.mp3

You have to listen to over half of it to get the point.  It's a F1
engine.  I don't recall if I first found this on PicList or elsewhere,
but I was able to re-find it pretty quick through Google.

I also found a description of the mp3 here:
http://www.petting-zoo.net/~deadbeef/archive/5304.html

Bradley

2005\04\06@130352 by Peter

picon face


On Tue, 5 Apr 2005, Carey Fisher - NCS wrote:

{Quote hidden}

In short, a dsp computer running in a chip takes snapshots of the desk
under the mouse. Successive snapshots show the features moved as the
mouse moves. The computer computes the difference between the pictures
using correlation and sends the difference to the computer as a mouse
packet.

Peter

2005\04\06@154610 by Barry Gershenfeld

face picon face
The special way that piano wire vibrates is called "resonance".  And the
adjustment likely changed the free length of the wire, until it
resonated.   This suggests that the "other" way of measuring the frequency
(RPM) can be had by low-pass filtering and looking for the largest
(zero-crossing) signal...effectively what that gauge did.   Interesting
gadget, though.  I'll watch for one at swap meets.

Barry

{Quote hidden}

2005\04\06@180608 by Glenn Jones

picon face
Right, I understood it was a resonanace, what I meant by some special
way was that I didn't know which resonance it was looking for, though
the lowest mode probably makes most sense. The adjustment did change
the free length as you suggested, but I didn't make that very clear.

On Apr 6, 2005 12:45 PM, Barry Gershenfeld <RemoveMEbarry_gTakeThisOuTspamzmicro.com> wrote:
{Quote hidden}

> -

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