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'[PICS] Strobes'
1998\10\28@081940 by Andy Kunz

flavicon
face
>circles of patterns, one for each desired speed.  If you figured out how
to make
>the patterns, you could print up anything you like on your laser or inkjet.

Some more info on the problem might help...

I'm looking at an 1/8" dia shaft with a 1.25" propeller on the end,
rotating between 1K and 60K RPM.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\28@103112 by Roger Marin

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face
A stack of super bright (2000mcd) red LED's with along with a high
current pulse driver/oscillator combo may be quick, dirty and cheap ...
just a thought.

--
Roger Marin
8825 S.E. Hawthorne Blvd.
Portland, OR, 97216-1821
voice: 503.253.3195
fax  : 503.253.0488

1998\10\28@125947 by Peter L. Peres

picon face
On Wed, 28 Oct 1998, Andy Kunz wrote:

> >circles of patterns, one for each desired speed.  If you figured out how
> to make
> >the patterns, you could print up anything you like on your laser or inkjet.
>
> Some more info on the problem might help...
>
> I'm looking at an 1/8" dia shaft with a 1.25" propeller on the end,
> rotating between 1K and 60K RPM.

Why didn't you say so ;) Is it going to be wet ? If so, a twin plastic
optical fiber arrangement with an IR laser and a common IR photodiode will
likely help you a lot. Prop blades are reflective enough for this in my
experience and the flexible twin fibers can be taped to a convenient place
for temporary use ;). You can probably use an IR led if pulsed fast. In
this case some trickery is required to get rid of the beat frequency. PICs
are as good as made for this. The input amplifier for the photodiode needs
to be a better one, probably a faster FET op-amp with the detector wired
as current generator (connect polarized photodiode to - input). 60,000 rpm
is only 1000 rot/sec or 4000 Hz for a 4-blade prop (not likely, more like
2 or 3 blades). If the LED is pulsed with 1 Amp pulses at 30 kHz as for IR
remote applications it should work ok.

The audio tach can be of two kinds: The one where you hear the speed as a
tone and the one where a tone is to be displayed as speed. The 1st method
is easy, connect an audio amp to the IR circuit described above. With 3
blades you get 50 Hz for 1k and 3000 Hz for 60,000. The 2nd method
involves a microphone and a Schmitt Trigger amplifier that supplies a
frequency to a counter. If the amplifier has some AGC, it will lock on the
loudest frequency around (such as, a nitro engine running full throttle
near it).  This last method works very well as I can confirm ;)

Peter

1998\10\28@141645 by Andy Kunz

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face
>Why didn't you say so ;) Is it going to be wet ? If so, a twin plastic

Not while I'm balancing it.  It's for a dynamic balancer along the lines of
what is used in full-size cars.  I'm sure some heli guys will like it.

>2 or 3 blades). If the LED is pulsed with 1 Amp pulses at 30 kHz as for IR
>remote applications it should work ok.

1A in an LED - what a concept!  What kind of duty cycle do you propose, the
standard 30%?

>tone and the one where a tone is to be displayed as speed. The 1st method

I want digital RPM display based upon frequency the boat is putting out.

>frequency to a counter. If the amplifier has some AGC, it will lock on the
>loudest frequency around (such as, a nitro engine running full throttle
>near it).  This last method works very well as I can confirm ;)

These are electric, but the idea is the same.  We are much quieter!

Do you have a schematic for an audio AGC which will give me the pulsing I
need?  That's the real hangup for me - converting it to RPM is just software.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\28@165511 by Sean Breheny

face picon face
At 01:37 PM 10/28/98 -0500, you wrote:
>>Why didn't you say so ;) Is it going to be wet ? If so, a twin plastic
>
>Not while I'm balancing it.  It's for a dynamic balancer along the lines of
>what is used in full-size cars.  I'm sure some heli guys will like it.

What does balance have to do with RPM? Please enlighten me! <G> It would
seem to me that prop imbalance causes the engine to wobble, but doesn't
significantly change the RPM.

Sean

+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
spam_OUTshb7TakeThisOuTspamcornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\10\29@002823 by shadedemon

picon face
Andy Kunz wrote:

> Do you have a schematic for an audio AGC which will give me the pulsing I
> need?  That's the real hangup for me - converting it to RPM is just software.

 Not sure if you need AGC here.  I've been toying with a
simple way for a light based similar idea.  You have a high
peak sound pressure when the exhaust first hits.  Just
compare that against a reference that is generated from the
peak but decays from the last peak.  But the ref is still
well above background noise when the next peak hits so only
peaks count.  And have a comparator that fires when the
input goes above the reference to indicate your next peak..

 MIC--gain--signal--->|---RC network
               |               |
               V               |
               -               |
               |               |
               +               -        lm339 inputs

The incoming peaks charge the RC network through the diode
to get a "near peak" average level.  But make the time
constant short enough that even if the next peak is a little
quieter the RC will have fallen a bit and you get a pulse
comparing the two.  Imagine an LED instead of a normal
diode.  RC should drop enough to make sure the LED lights
when the next peak arrives.  But should stay high enough
that other background noise won't be close to lighting the
LED.  Only problem with this way is is making decay enough
to detect 60khz pulses and not too much for 1khz where it
falls too much and other background noise can register.
 So just suit time constant to how fast boat will move away
from you..  And compare incoming signal vs a voltage divided
2/3 or 3/4 of whats on the cap.  Then you get your wide
frequency range, but still only register pulses near your
average peak.  And if your peaks fall, the level they're
compared to will as well, just slowly.
 I'm doing something similar using an IR LED and photo to
index a rotating system vs the not rotating part.  This way
is a simple circuit and the value held in the C for
comparison is so close to the peak that changes in ambient
lighting/IR will be ignored.  If you want a really long
constant just use two caps in series for the voltage divider
and no R..
 Gain doesn't matter since the other peaks are the
reference, and peaks from the initial exhaust opening are so
high it should ignore other sounds.  When you get a peak,
ignore anything else for 1/120000th second (halfway to your
next possible peak) and you should be noise immune..

Take with a grain of salt, since I'm working on a different
part of the system and have only done a little testing on
this, but that part seems to be ok so far..

Alan

1998\10\29@005137 by tjaart

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face
Alan King wrote:

{Quote hidden}

I've used this with great success on electret mic's. You want
to have good gain, but no tuning. The non-inv input of a
TL074 was hooked to the tail end of an RC network with a
time constant of 2s. The inv input was hooked to the positive
side of the electret. It worked pretty well. If you divide the
non-inv input, you can get away with a single supply and LM324's.

If you want to get really fancy, you can use an intrumentation
op-amp setup with the two inputs taken from the positive and
negative sides of the mic. Use a series resistor between the
negative side of the mic, and ground.

If what I said didn't make sense, tell me, and i'll try again ;)

--
Friendly Regards

Tjaart van der Walt
.....tjaartKILLspamspam@spam@wasp.co.za

|--------------------------------------------------|
|                WASP International                |
|R&D Engineer : GSM peripheral services development|
|--------------------------------------------------|
|SMS tjaartspamKILLspamsms.wasp.co.za  (160 chars max)|
|     http://www.wasp.co.za/~tjaart/index.html     |
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|          WGS-84 : 26¡10.52'S 28¡06.19'E          |
|--------------------------------------------------|

1998\10\29@115758 by John Payson

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face
|At 01:37 PM 10/28/98 -0500, you wrote:
|>>Why didn't you say so ;) Is it going to be wet ? If so, a twin plastic
|>
|>Not while I'm balancing it.  It's for a dynamic balancer along the lines of
|>what is used in full-size cars.  I'm sure some heli guys will like it.

|What does balance have to do with RPM? Please enlighten me! <G> It would
|seem to me that prop imbalance causes the engine to wobble, but doesn't
|significantly change the RPM.

I think the idea is that the strobe should run at a right a few
hertz faster or slower than the motor's rotation speed; this would
have the effect of visually slowing the wobble to the point that
it could be usefully seen.  If there is a marking at one spot on
the shaft, the user could see how the direction of the wobble com-
pares with that mark; he could then (after stopping the motor of
course!) adjust the weight distribution to correct for the obser-
ved wobble.

Without such a device, a user might notice that the rotor is wob-
bling quite badly but still have no clue where weight needs to be
added or removed to solve the problem.

1998\10\29@132122 by Peter L. Peres

picon face
On Wed, 28 Oct 1998, Sean Breheny wrote:

> At 01:37 PM 10/28/98 -0500, you wrote:
> >>Why didn't you say so ;) Is it going to be wet ? If so, a twin plastic
> >
> >Not while I'm balancing it.  It's for a dynamic balancer along the lines of
> >what is used in full-size cars.  I'm sure some heli guys will like it.
>
> What does balance have to do with RPM? Please enlighten me! <G> It would
> seem to me that prop imbalance causes the engine to wobble, but doesn't
> significantly change the RPM.

Unbalanced devices cause vibration in the structure at various rpms. This
can be bad enough to make things fall apart. So one reason for balancing
is to get rid of the worst vibration points and to learn the others so as
not to run the boat on one of them and have it come back with a 1mm play
in the prop bearing and without the keel (if used).

Peter

1998\10\29@132132 by Peter L. Peres

picon face
On Wed, 28 Oct 1998, Andy Kunz wrote:

> >Why didn't you say so ;) Is it going to be wet ? If so, a twin plastic
>
> Not while I'm balancing it.  It's for a dynamic balancer along the lines of
> what is used in full-size cars.  I'm sure some heli guys will like it.

What do you use for accelerometers and do you index it or what ? Because
if you index the axis position to determine which way the inbalance vector
pulls then you already have a speed-related signal that you can tap into.

> >2 or 3 blades). If the LED is pulsed with 1 Amp pulses at 30 kHz as for IR
> >remote applications it should work ok.
>
> 1A in an LED - what a concept!  What kind of duty cycle do you propose, the
> standard 30%?

IR remote control leds run at that power level with a duty cycle of 10%
(3us on in 30us or so). They are quite happy with it. A PIC can easily do
that by flipping an output bit with a nop or two between the on and off
commands. And where did you get the standard 30% from ? Is it an American
standard ?

{Quote hidden}

I don't know what the sound level is, that you start out with. By the way,
did you say ELECTRIC ? Multi-pole electric motors with a switched
collector draw current in gobs as the collector switches coils, and there
is a way to build even electronic stabilizers like this. No, you don't
need a pickoff resistor, use the length of cable of the '+' wire from the
regulator f.ex. A LM358 wired 1/2 as x 100 AC amplifier with differential
input and 1/2 as pulse shaper (comparator) should do what you want. Try
this, with 2 crocodile clamps to attach to the engine wire and a scope as
output (before the shaper). Some tinkering may be required. The crocos
attach one to the regulator '+' output and one to the motor '+' input. The
wire between them acts as sense shunt. Some amount of low-passing the 358
will be required.

Another way to get at the frequency of a running DC motor is to put a
pickup coil on it. A phone suction cup coil should work and so should a
vrac-wound ferrite rod antenna. The amplifier is the same. This should
work through the boat body (fiberglass or carbon I presume). Magnetic
pickups do not like to be in the same room with variacs and other mains
operated large transformers and motors, so maybe try the shunt method
first.

hope this helps,

Peter

1998\10\29@154230 by Sean Breheny

face picon face
At 06:57 PM 10/29/98 +0000, you wrote:
>Unbalanced devices cause vibration in the structure at various rpms. This
>can be bad enough to make things fall apart. So one reason for balancing
>is to get rid of the worst vibration points and to learn the others so as
>not to run the boat on one of them and have it come back with a 1mm play
>in the prop bearing and without the keel (if used).

Hi Peter,

I understand WHY unbalance causes vibration. What I don't understand is how
a Tachometer helps you to determine the degree of imbalance.

John Payson suggested that it helped by allowing the use of a strobe which
was synchonized with the rotation to allow the prop to seem to stand still,
so that we could see the wobbling. I'll have to think about this a bit, but
I'm not convinced that strobing will make the wobbling rate seem slower to
the eye.

Sean


>
>Peter
>
+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
.....shb7KILLspamspam.....cornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\10\29@160727 by Andy Kunz

flavicon
face
>Without such a device, a user might notice that the rotor is wob-
>bling quite badly but still have no clue where weight needs to be
>added or removed to solve the problem.

Thanks, John.  Your explanation sure beat mine!

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\29@160730 by Andy Kunz

flavicon
face
>What do you use for accelerometers and do you index it or what ? Because

Not that far along yet.  I'm still using an Eye, Mark I.

>IR remote control leds run at that power level with a duty cycle of 10%
>(3us on in 30us or so). They are quite happy with it. A PIC can easily do

No, a std 38KHz IR is 8uS on and 26 off.  Check the NEC documentation, or
just about any IR chip.

>commands. And where did you get the standard 30% from ? Is it an American
>standard ?

Japanese --> universal <G>

>I don't know what the sound level is, that you start out with. By the way,
>did you say ELECTRIC ? Multi-pole electric motors with a switched

Yes.  We race them at about 50mph around an oval.  We dump 2 AH in 90 seconds.

>is a way to build even electronic stabilizers like this. No, you don't

Stabilizer?  ?

>Another way to get at the frequency of a running DC motor is to put a
>pickup coil on it. A phone suction cup coil should work and so should a

The motor is 100' away traveling at 50mph.  Sound is the only possibility.

I have a tach in my data logger (on board some boats, but not all have
enough room), now I need an external one.

Thanks.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\29@163355 by Andy Kunz

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face
>I understand WHY unbalance causes vibration. What I don't understand is how
>a Tachometer helps you to determine the degree of imbalance.

The tach isn't used for balancing, it's used to measure performance.
Slightly related, but as a measurement of increase, not to balance per se.

>I'm not convinced that strobing will make the wobbling rate seem slower to
>the eye.

Yes, it does.  Actually, the strobe light is to be run either off a pot or
by watching the rotation of the propeller, under user selection.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\30@005119 by Andy Kunz

flavicon
face
>What does balance have to do with RPM? Please enlighten me! <G> It would
>seem to me that prop imbalance causes the engine to wobble, but doesn't
>significantly change the RPM.

Have you ever been to a speed shop?  You need to get your tires balanced
for operation at the expected speed.  Harmonics.

Oh, it does!  When you're spinning at 60K RPM especially.

You can be perfectly balanced dimensionally (same outline both blades) and
statically (it stays level on the balancer), but until you spin it you
don't know for sure.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\30@014151 by Sean Breheny

face picon face
Hi Andy,

At 09:41 AM 10/29/98 -0500, you wrote:
>Have you ever been to a speed shop?  You need to get your tires balanced
>for operation at the expected speed.  Harmonics.

So, you're saying that they actually listen for harmonics generated by the
wobbling? I would think that the wobbling would be at the same or less
frequency then the rotational frequency of the object.

>
>Oh, it does!  When you're spinning at 60K RPM especially.

Andy, are you using jet powered boats? <G> I have never heard of a model
engine that spins a prop at 60,000 RPM in AIR let alone WATER!!!!!

I have an RC plane with a .40 cu in engine and it tops out at 16,000 RPM
with a 10x6 prop (well, I never measured it, but that's what the specs say).

>
>You can be perfectly balanced dimensionally (same outline both blades) and
>statically (it stays level on the balancer), but until you spin it you
>don't know for sure.

Well, I have never worried about anything other than static balancing on my
prop. The only other way that it could be unbalanced (as far as I can see)
would be if there were more mass toward the back of one blade and toward
the front on another. If you get this advanced, how do you adjust your
props? I just sand the outer edge of the flat side of mine to remove moment
from that side.

Sean


>
>Andy
>
>==================================================================
>Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
>==================================================================
>
+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
EraseMEshb7spam_OUTspamTakeThisOuTcornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\10\30@061958 by Peter L. Peres

picon face
On Thu, 29 Oct 1998, Andy Kunz wrote:

> >IR remote control leds run at that power level with a duty cycle of 10%
> >(3us on in 30us or so). They are quite happy with it. A PIC can easily do
>
> No, a std 38KHz IR is 8uS on and 26 off.  Check the NEC documentation, or
> just about any IR chip.

You can use 3 usec with the same parts. The range is slightly better, and
RFI is harder to control, but the FCC is far away from here ;)

> >commands. And where did you get the standard 30% from ? Is it an American
> >standard ?
>
> Japanese --> universal <G>

Ah, ok. ;)

> >I don't know what the sound level is, that you start out with. By the way,
> >did you say ELECTRIC ? Multi-pole electric motors with a switched
>
> Yes.  We race them at about 50mph around an oval.  We dump 2 AH in 90 seconds.

So dump 80 Amps into a 0.005 ohm connection wire. Gives 0.4V and it's not
DC ;)

> >is a way to build even electronic stabilizers like this. No, you don't
>
> Stabilizer?  ?

I mean regulator.

> >Another way to get at the frequency of a running DC motor is to put a
> >pickup coil on it. A phone suction cup coil should work and so should a
>
> The motor is 100' away traveling at 50mph.  Sound is the only possibility.
>
> I have a tach in my data logger (on board some boats, but not all have
> enough room), now I need an external one.

Radio. Get one of those wireless data module pairs and do something smart
with it. I guess the simplest way would be to buy a 'bug' transmitter kit
for FM and connect the mike input directly on the motor wire as described.
A pot may be required to get the volume down. A bug with AGC is better.
Then listen with a FM radio tuned to it. This should be small enough to
fit anywhere.

Peter

1998\10\30@062008 by Peter L. Peres

picon face
On Thu, 29 Oct 1998, Sean Breheny wrote:

> At 06:57 PM 10/29/98 +0000, you wrote:
> >Unbalanced devices cause vibration in the structure at various rpms. This
> >can be bad enough to make things fall apart. So one reason for balancing
> >is to get rid of the worst vibration points and to learn the others so as
> >not to run the boat on one of them and have it come back with a 1mm play
> >in the prop bearing and without the keel (if used).
>
> Hi Peter,
>
> I understand WHY unbalance causes vibration. What I don't understand is how
> a Tachometer helps you to determine the degree of imbalance.

The tachometer can be used to determine where the vibration occurs (minor
vibration that is not to be corrected) and then make a chart to tell the
pilot what engine setting NOT to use.

> John Payson suggested that it helped by allowing the use of a strobe which
> was synchonized with the rotation to allow the prop to seem to stand still,
> so that we could see the wobbling. I'll have to think about this a bit, but
> I'm not convinced that strobing will make the wobbling rate seem slower to
> the eye.

;) The axis wobbling will be at the rate of rotation in most cases so if
the strobe flashes in sync with the rotation the whole picture appears
frozen, with the axis bent out in the direction of mass imbalance. If
there is a colored mark on the axis or on a blade, you can reference the
direction of imbalance to this, stop the motor and correct, then redo from
start.

Peter

1998\10\30@090708 by Keith H

flavicon
face
On Thu, 29 Oct 1998, Andy Kunz wrote:

> >IR remote control leds run at that power level with a duty cycle of 10%
> >(3us on in 30us or so). They are quite happy with it. A PIC can easily do
>
> No, a std 38KHz IR is 8uS on and 26 off.  Check the NEC documentation, or
> just about any IR chip.

IR handsets are anything but standard.

Carrier modulation can be from around 33 to 40 kHz, and sometimes 60 kHz.
I analysed handsets from my house, and found 7us on 21 us off was common
though one handset used 7us on 14 us off.

I wrote some PIC code to transmit various handset signals, and it worked.

The commonly quoted website
       falcon.arts.cornell.edu/~dnegro/IR/REMOTES/
is full of bugs!

BTW, anybody know what phosphor is used to convert IR to white light
in white LEDs? Is it cheap, non-toxic, and robust outside LED pacakging?

1998\10\30@093803 by Andy Kunz

flavicon
face
>So, you're saying that they actually listen for harmonics generated by the
>wobbling? I would think that the wobbling would be at the same or less
>frequency then the rotational frequency of the object.

"Listen" is the wrong word, but yes, the balance of your tire will change
at different RPMs.  How that affects your driving is also dependent upon
the suspension of your car.

>Andy, are you using jet powered boats? <G> I have never heard of a model
>engine that spins a prop at 60,000 RPM in AIR let alone WATER!!!!!

Motor, not engine.  60K isn't hard for a DC motor.  Check out the
advertisements from Model Electronics for their War Emergency Power series.
I use their Turbo 10+ motor in my scale boats, but with the timing cranked
to the physical limits (to boost RPM).

>Well, I have never worried about anything other than static balancing on my
>prop. The only other way that it could be unbalanced (as far as I can see)

At 16K it isn't as important, but with the mass your spinning it could be.

Get yourself a Top Flight magnetic balancer and give the prop a spin.
You'll see.

>the front on another. If you get this advanced, how do you adjust your
>props? I just sand the outer edge of the flat side of mine to remove moment

Boats use metal props, and I just oil sand the thickness of the blade,
usually.

You ought to try dimensional balancing first.  Press the image of the prop
into Play-Doh, rotate prop 180 degrees, and see how they line up.

Some props are horrendous.  APC's are good, imho.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\30@093807 by Andy Kunz

flavicon
face
>You can use 3 usec with the same parts. The range is slightly better, and
>RFI is harder to control, but the FCC is far away from here ;)

Good idea!

>Radio. Get one of those wireless data module pairs and do something smart

I'm investigating that angle, but I don't have room in all the boats.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================


'[PICS] Strobes'
1998\11\03@140318 by Peter L. Peres
picon face
On Tue, 3 Nov 1998, Andy Kunz wrote:

> Do you have a schematic for this as well?  I think I'm missing something ...

Schematic to work with LM324/LM358:


                      Switch
                         /
+ Battery O-------------o/ o-------------O + Motor





- Battery O-*--------------------------*-O - Motor
           |                          |
           |                          |
           |                          |        1/4 LM324
           |                          |   |\
           |                          +---+ \
           |                              |  >--*-||-O Audio out
          ===                         +---- /   |
          GND 324                     |   |/    |
                                      |         |
                                      +---------+

The 324 receives power from somewhere else (can be +Battery). The output
should be pretty loud in any amp at 80A current. It may be necessary to
turn the direct feedback network into something else to obtain a low-pass
characteristic but the 324 is slow enough at 5V so as not to propagate
spikes.

The output can be fed (through a volume pot) into the mike input of bug Tx
or directly into an amplifier (small guitar amp ?). Start out with a low
volume.

I once used a setup like this to hunt a rusted ground connection bolt in a
large machine so I know it works.

With some cunning you can take this signal and amplify and limit it to
synchronize a PLL that can drive a strobe. A median filter is a good idea
and the PLL can be a PIC. The output frequency is a whole multiple of the
RPM (usually number of coil armatures on rotor x RPM) and depends on the
type of motor.

Peter

1998\11\03@154247 by paulb

flavicon
face
Peter L. Peres wrote:

> Schematic to work with LM324/LM358:

 Peter, that circuit makes no sense at all!  You are using a voltage-
follower with no gain to buffer a signal whose impedance is a few
hundredths of an ohm!  Total waste of time!

 If OTOH you were to provide a *gain* in the op-amp, say 500 times, to
limit and drive a logic gate, it would be useful.
--
 Cheers,
       Paul B.

1998\11\04@112721 by Peter L. Peres

picon face
On Wed, 4 Nov 1998, Paul B. Webster VK2BZC wrote:

> Peter L. Peres wrote:
>
> > Schematic to work with LM324/LM358:
>
>   Peter, that circuit makes no sense at all!  You are using a voltage-
> follower with no gain to buffer a signal whose impedance is a few
> hundredths of an ohm!  Total waste of time!

That is correct, however it was to clarify the idea. The notes explain
why the amp is not used as is but as an amplifier and low pass filter.

Peter

>   If OTOH you were to provide a *gain* in the op-amp, say 500 times, to
> limit and drive a logic gate, it would be useful.

The amp already limits, depending on offset vs. input signal the output
will be rectified or clipped. You don't really need to amplify, just
remove the feedback connection. If the offset is the wrong way swap the +
and - inputs. ;) This yields Vdd size pulses at the output but you need to
low-pass in software.

Peter

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