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'[EE]: stepper "digital" knob viability'
2002\06\28@062622 by Roman Black

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face
(re stepper motor for a digital knob thread)
I've just been playing with a 12v unipolar "surplus"
stepper from an old 5.25 disk drive. Connected it to
the CRO and used a clothes peg for an accurate "knob".

Output voltage doesn't seem to be a problem, even the
slowest one-detent moves make +/-200mV or more, 400mV
P/P, a decent speed (like 0.1 rev/sec) gives +/-1v, and
anything like a spin (>0.3 rev/sec) slams the volts into
the 4.6v safety stop (I used a 4.6v zener in parallel
with each coil).

So using 2 transistors biased at 500mV (just off) you
could sense positive going pulses over 100mV, would give
decent "dial" operation for any real twiddling speed.
Yes it is possible to move the knob if you really try
without triggering a 100mV setpoint, but it's not easy.
Ok, so not as good as optical dial encoder on that point,
but better in terms of bearing/shaft/detent/mounting
quality, etc which matter a lot in high use or high
quality application. And probably price too! :o)

I don't think the problem will be detecting pulses but
in the decoding. Detecting only the + pulses is easy and
will give quadrature encoding (90 degree phase) when the
dial is turning. So turning dial will work well. The
problem will be in tiny fractional moves. There were
200 obvious "detents", but some (half!) produce - pulses.

Looking at one coil only, you can turn the knob one detent
and it makes a + pulse. Turn it another detent and it makes
a - pulse.

I really don't know how to get around this problem. For
any real turning speed the thing will work great, but for
fractional moves there will be 1 detent in 4 that makes
- pulses on both coils, which won't be detected.
This doesn't matter if the knob is turned more than a few
detents and also doesn't matter if the tiny movements
don't need to be measured exactly equivalent by degree.

The very easiest solution would be to detect when both +
pulses occur together, then when one ends before the other
the PIC logs a "pulse" in that direction. This would only
increment one pulse per 4 detents, or 50 pulses per shaft
rotation but work very reliably. 2 transistors, 4 1N4004
diodes, handful resistors.
-Roman


Peter L. Peres wrote:
{Quote hidden}

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2002\06\28@063230 by Joe Farr

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And what would be really cool using a stepper motor is when you power up the project, the control 'moves' back to the last stored position nice and smooth...

{Original Message removed}

2002\06\28@081235 by Bob Ammerman

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>And what would be really cool using a stepper motor is when you power up
the project, the control 'moves' back to the last >stored position nice and
smooth...

Or when  you use the infrared remote, the control tracks the action of the
remote.

Bob Ammerman
RAm Systems

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2002\06\28@082044 by Joe Farr

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You have to admit, it has a certain "I want one now" feel about it :-)



-----Original Message-----
From: Bob Ammerman [spam_OUTrammermanTakeThisOuTspamADELPHIA.NET]
Sent: 28 June 2002 13:06
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: Re: [EE]: stepper "digital" knob viability


>And what would be really cool using a stepper motor is when you power up
the project, the control 'moves' back to the last >stored position nice and
smooth...

Or when  you use the infrared remote, the control tracks the action of the
remote.

Bob Ammerman
RAm Systems

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2002\06\28@084132 by Roman Black

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Joe Farr wrote:
>
> You have to admit, it has a certain "I want one now" feel about it :-)

> >And what would be really cool using a stepper motor is when you power up
> the project, the control 'moves' back to the last >stored position nice and
> smooth...
>
> Or when  you use the infrared remote, the control tracks the action of the
> remote.


I just injected 25mA into the test setup, with the
motor driven by 4 PIC pins, 25mA each in unipolar
mode 2-phase on mode, there is *enough* torque to
turn the motor. :o)
Motor:
(norm 12v 150mA from an old disk drive)
63 ohms, 1.6v @ 25mA per coil unipolar

So this is viable! 2 PIC pins to sense dial being turned,
another 4 pins to turn it. With unipolar mode and such
low coil current you don't even need flyback diodes etc.
Very nice. :o)
-Roman

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2002\06\28@091300 by Alan B. Pearce

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>And what would be really cool using a stepper
>motor is when you power up the project, the
>control 'moves' back to the last stored position
>nice and smooth...

>Or when  you use the infrared remote, the control
>tracks the action of the remote.

.........

>You have to admit, it has a certain "I want one
>now" feel about it :-)

Now imagine the head scratching of the guy trying to reverse engineer your
project - that knob is only connected to a motor - where is the pot
?????????

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2002\06\28@093354 by Alan B. Pearce

face picon face
>So this is viable! 2 PIC pins to sense dial being
>turned, another 4 pins to turn it. With unipolar
>mode and such low coil current you don't even need
>flyback diodes etc.
>Very nice. :o)

Until one of the rugrats starts playing with it and spinning it at high
speed with the power off :))

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2002\06\28@114437 by Erik Jacobs

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> (re stepper motor for a digital knob thread)
> I've just been playing with a 12v unipolar "surplus"
> stepper from an old 5.25 disk drive. Connected it to
> the CRO and used a clothes peg for an accurate "knob".

Well, my questions are:

A) how small can one of these be (in comparison to a rotary encoder)?
B) how cheaply can one be had (in comparison to a rotary encoder)?

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2002\06\28@115115 by Pic Dude

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My all-in-one Sony mini component system does that (it's
about 14 years old).  I don't think it's a rotary encoder
cause it has a definite start and end, and has no detents
(very smooth).  But altering the volume on the remote will
change the physical position of the rotary knob.  Has a
cool little LED on it too, to indicate the setting/position.

Cheers,
-Neil.



{Original Message removed}

2002\06\28@115124 by Spehro Pefhany

picon face
At 11:46 AM 6/28/02 -0400, you wrote:
> > (re stepper motor for a digital knob thread)
> > I've just been playing with a 12v unipolar "surplus"
> > stepper from an old 5.25 disk drive. Connected it to
> > the CRO and used a clothes peg for an accurate "knob".
>
>Well, my questions are:
>
>A) how small can one of these be (in comparison to a rotary encoder)?

As small as some. See, for example, the stepper used in a 3.5" FDD.

>B) how cheaply can one be had (in comparison to a rotary encoder)?

They are free if you are a hobbyist and don't mind pulling them out
of old stuff, otherwise they will cost more money at pretty much ANY
quantity level compared to mechanical encoders, but may be cheaper than
a decent optical encoder.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\06\28@115607 by Spehro Pefhany

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At 10:47 AM 6/28/02 -0500, you wrote:
>My all-in-one Sony mini component system does that (it's
>about 14 years old).  I don't think it's a rotary encoder
>cause it has a definite start and end, and has no detents
>(very smooth).  But altering the volume on the remote will
>change the physical position of the rotary knob.  Has a
>cool little LED on it too, to indicate the setting/position.

These are motorized pots. They have the advantage that they
maintain their setting with power-off, and don't require
a "home" switch as a stepper would. They used to be hideously
expensive (and professional quality), became cheap (and consumer
quality) as a gimmick in stereos, now perhaps are going to get
hard to find again.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
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2002\06\28@120119 by Pic Dude

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(b) Jameco has some small stepper motors, for as low as
55 cents, in single-piece quantities.

Cheers,
-Neil.



{Original Message removed}

2002\06\28@121306 by Brendan Moran

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For the rotary optical encoder we were using for position control here, it
costs $85 to replace the beggars, and they do, eventually, break down.  I've
had a rotary optical encoder that produced quadrature for 270 deg, and
something else for 90 deg.  That is soooo hard to troubleshoot.  That's why
I'm vying for killing the rotary encoder position control scheme.

In short, 55 cents for a position sensor seems like a very fine deal to me.

--Brendan
----- Original Message -----
From: "Pic Dude" <EraseMEpicdudespam_OUTspamTakeThisOuTAVN-TECH.COM>
To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Friday, June 28, 2002 8:58 AM
Subject: Re: [EE]: stepper "digital" knob viability


> (b) Jameco has some small stepper motors, for as low as
> 55 cents, in single-piece quantities.
>
> Cheers,
> -Neil.

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2002\06\28@121921 by Robert Rolf

picon face
The Sony control has a normal stacked pot with a tiny DC servo motor hanging
off the end. You can probably get it as a replacement part, but it won't be
cheap. There are probably other consumer systems with this kind of pot in it.

And wasn't the whole point of a rotary encoder the fact that it didn't HAVE
a 'home' position? If you want a powered control, why not use an R/C servo
with a low gear ratio so it can be 'back driven' or with a friction clutch
and continous motion (like the modified Paralax robot servo).

And if you used a PIC with comparator inputs (16F87xA series) you'd only
need 4 pins since you could tri-state the drive pins when you're not
driving the motor. Just be sure to have zener clamps on the motor coils
so that it's 'childproof'.

R

Pic Dude wrote:
{Quote hidden}

> {Original Message removed}

2002\06\28@123622 by Pic Dude

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> "And wasn't the whole point of a rotary encoder the fact that it
> didn't HAVE a 'home' position?"

Yep, you are correct.  The discussion sort of morphed into this.

Here's another idea -- use an R/C servo, and mount the knob on it
free-floating.  That way, turning the knob does not turn the
servo.  Now mount 2 microswitches on the servo arm with the knob
hitting (and stopping on) the microswitches turned cw or ccw.
Now, move the servo accordingly with code.

Only problem is "feel".  The micro switches would need to be
small "pots" with springs to indicate how much pressure is being
put on the knob, so it can rotate at a variable speed based on
how fast the user is trying to move it.

Ah yes, Rube Goldberg is my hero!

Cheers,
-Neil.



{Original Message removed}

2002\06\29@080708 by Peter L. Peres

picon face
Roman, I did not consider that you would have to resolve single detents.
You are right about there being one detent where there are two (-) pulses.
I propose the following two solutions:

1. Use a Schmitt trigger on each input. The Schmitts will 'integrate' the
pularised pulses and produce normal quardature outputs (sin,cos, indigital
form). The Shmitt can be implemented with the opamps I suggested.

Try these values: 10K/10K and decouple to gnd with 1uF for reference,
connect motor common here.

Each trigger has - input to referencee, 1K from (+) input to motor phase,
1M positive feedback from out to (+) input and 4k7 pullup on the output.
The 1M may have to be reduced to up to 100k to improve noise immunity.

2. Build two fliflops using IIL technology with a few discrete
transistors, each controlled by a motor phase. IIL has low logic levels
and it should work with the motor voltages properly.

Peter

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2002\06\29@080736 by Peter L. Peres

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On Fri, 28 Jun 2002, Spehro Pefhany wrote:

>At 10:47 AM 6/28/02 -0500, you wrote:
>>My all-in-one Sony mini component system does that (it's
>>about 14 years old).  I don't think it's a rotary encoder
>>cause it has a definite start and end, and has no detents
>>(very smooth).  But altering the volume on the remote will
>>change the physical position of the rotary knob.  Has a
>>cool little LED on it too, to indicate the setting/position.
>
>These are motorized pots. They have the advantage that they
>maintain their setting with power-off, and don't require
>a "home" switch as a stepper would. They used to be hideously
>expensive (and professional quality), became cheap (and consumer
>quality) as a gimmick in stereos, now perhaps are going to get
>hard to find again.

You seem to know the 'good old ones'. Do you happen to know where one
could get some surplus motor-tuned air variable caps ? I have no info on
this at all and I am toying with the idea of making myself a remote tuned
antenna preselector. I have also considered building one out of ganged air
variables and a carrier current remote control. I have a precision dc
servo to turn them (1:500 backlash free gears).

Peter

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2002\06\29@080747 by Peter L. Peres

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On Fri, 28 Jun 2002, Erik Jacobs wrote:

>> (re stepper motor for a digital knob thread)
>> I've just been playing with a 12v unipolar "surplus"
>> stepper from an old 5.25 disk drive. Connected it to
>> the CRO and used a clothes peg for an accurate "knob".
>
>Well, my questions are:
>
>A) how small can one of these be (in comparison to a rotary encoder)?

About 8mm diameter and 4mm long is the smallest in current use. Not
available as surplus though.

>B) how cheaply can one be had (in comparison to a rotary encoder)?

A surplus stepper (large) will be about $1 from surplus places. Beware
that a good quality stepper ordered from the manufacturer can cost $25++
without his even trying hard.

I think that using steppers for this is only viable because they are
available surplus for nothing.

Peter

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2002\06\29@080758 by Peter L. Peres

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On Fri, 28 Jun 2002, Joe Farr wrote:

>You have to admit, it has a certain "I want one now" feel about it :-)

Unless you already own a hifi component that has been doing that for ~8
years or so. I don't, but I also don't feel like having one.

Peter

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2002\06\29@082023 by Peter L. Peres

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On Fri, 28 Jun 2002, Joe Farr wrote:

>And what would be really cool using a stepper motor is when you power up
>the project, the control 'moves' back to the last stored position nice
>and smooth...

Hehe. Let's see, using a ULN series chip it should work at least for
unipolar motors. The readout amp should be built to take this punishment.

Peter

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2002\06\29@082036 by Peter L. Peres

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On Fri, 28 Jun 2002, Pic Dude wrote:

>My all-in-one Sony mini component system does that (it's
>about 14 years old).  I don't think it's a rotary encoder
>cause it has a definite start and end, and has no detents
>(very smooth).  But altering the volume on the remote will
>change the physical position of the rotary knob.  Has a
>cool little LED on it too, to indicate the setting/position.

Look up ALPS and other motorized potentiometer units. Available as spare
parts eveyrwhere. DC motor with gears and slipclutch drives twin
potentiometers.

Peter

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2002\06\29@082042 by Peter L. Peres

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On Fri, 28 Jun 2002, Alan B. Pearce wrote:

>>So this is viable! 2 PIC pins to sense dial being
>>turned, another 4 pins to turn it. With unipolar
>>mode and such low coil current you don't even need
>>flyback diodes etc.
>>Very nice. :o)
>
>Until one of the rugrats starts playing with it and spinning it at high
>speed with the power off :))

There are enough diodes built into the PIC. However the project may come
to life. Crank-powered projects ? ;-) (put four NiCds directly on the
power rail of the PIC - they will charge from cranking)

Peter

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2002\06\29@121304 by Spehro Pefhany

picon face
At 12:40 PM 6/29/02 +0300, you wrote:

>You seem to know the 'good old ones'. Do you happen to know where one
>could get some surplus motor-tuned air variable caps ?

No idea, I'd start at my two favorite surplus places that carry this
sort of thing:

C&H Surplus in Pasadena: http://www.candhsales.com
Toronto Surplus in TO:   http://www.torontosurplus.com

Neither place gives stuff away, but they might have something like
that around. I don't buy a lot of surplus, only get to each once year or
so.

>I have no info on
>this at all and I am toying with the idea of making myself a remote tuned
>antenna preselector. I have also considered building one out of ganged air
>variables and a carrier current remote control. I have a precision dc
>servo to turn them (1:500 backlash free gears).

Sounds like it would work very nicely. You're right to be concerned about
backlash if you are going to be automatically tuning it, backlash is
a major nasty when it comes to designing the controller.

Best regards,

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2002\06\29@195159 by Peter L. Peres

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On Sat, 29 Jun 2002, Spehro Pefhany wrote:

>At 12:40 PM 6/29/02 +0300, you wrote:
>
>>You seem to know the 'good old ones'. Do you happen to know where one
>>could get some surplus motor-tuned air variable caps ?
>
>No idea, I'd start at my two favorite surplus places that carry this
>sort of thing:
>
>C&H Surplus in Pasadena: http://www.candhsales.com
>Toronto Surplus in TO:   http://www.torontosurplus.com
>
>Neither place gives stuff away, but they might have something like
>that around. I don't buy a lot of surplus, only get to each once year or
>so.

Okay, thanks.

>>I have no info on
>>this at all and I am toying with the idea of making myself a remote tuned
>>antenna preselector. I have also considered building one out of ganged air
>>variables and a carrier current remote control. I have a precision dc
>>servo to turn them (1:500 backlash free gears).

>Sounds like it would work very nicely. You're right to be concerned about
>backlash if you are going to be automatically tuning it, backlash is
>a major nasty when it comes to designing the controller.

I was thinking of a manual control, for a start. I do not know what kind
of signals I can get (I live in a city that thinks RFI is a brand of
cheese - nobody cares about EMI filters and such). That's why I hope a
good preselector will help me. The signal on a whip is terrible even with
all the computers and other noisemaking machines shut down.

Peter

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2002\06\29@200840 by Jim

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Peter wrote:

   "(I live in a city that thinks RFI is a
    brand of cheese - nobody cares about EMI
    filters and such). That's why I hope a
    good preselector will help me."

No amount of 'preselectoring' or filtering is going to
correct a 'bad' S/N (SIgnal to Noise) ratio due
to computer noise and other urban electrical noise
that appears "in-band and on-channel".

If, however, your receiver is experiencing "Front
End Overload" from close-by AM or SW broadcast stations
THEN a preselector can do some good!

I'm putting together a design right now that solves
a 160 M (1.8 - 2.0 MHz) problem owing to a LOT
of AM broadcasters in this area - including an
omni-directional 10 KW 1.7 MHz station.

It's been trick getting a low IL (Insertion Loss) across
the band of interest along with +40 dB of rejection
starting at 1.705 KHz and below. The second proto is
being built now with an eye on reproducability since
I was able to meet the design requirements ...

Jim


{Original Message removed}

2002\06\30@053153 by Roman Black

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Peter L. Peres wrote:

> >>You seem to know the 'good old ones'. Do you happen to know where one
> >>could get some surplus motor-tuned air variable caps ?

> I was thinking of a manual control, for a start. I do not know what kind
> of signals I can get (I live in a city that thinks RFI is a brand of
> cheese - nobody cares about EMI filters and such). That's why I hope a
> good preselector will help me. The signal on a whip is terrible even with
> all the computers and other noisemaking machines shut down.


Hi Peter, I have seen many types of motorised pots
in appliances, with some types the pot device can
be separated from the motor/gearbox part, usually by
2 bent over metal tags. The pot part had a standard
round shaft with one flat. I'm sure you could get a
variable cap with this size shaft, and with some easy
fiddling fit it to the motor unit.
-Roman

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2002\06\30@055101 by Roman Black

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That's a brilliant idea, using hysteresis so that
the negative pulse is detected too. Just keeping on
with the "minimum parts" idea I wonder if this could
be implemented by adding a capacitor to the single
transistor circuit, so the + pulse charges it and
the - pulse discharges it. This might give good
fractional response but will probably generate the
occasional false pulse as the cap discharges after
the thing stops turning.
-Roman


Peter L. Peres wrote:
{Quote hidden}

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2002\06\30@161412 by Peter L. Peres

picon face
On Sat, 29 Jun 2002, Jim wrote:

>Peter wrote:
>
>    "(I live in a city that thinks RFI is a
>     brand of cheese - nobody cares about EMI
>     filters and such). That's why I hope a
>     good preselector will help me."
>
>No amount of 'preselectoring' or filtering is going to
>correct a 'bad' S/N (SIgnal to Noise) ratio due
>to computer noise and other urban electrical noise
>that appears "in-band and on-channel".

I aggree. It is wideband hash and impulse noise from 'spark gap
transmitters'.

>If, however, your receiver is experiencing "Front
>End Overload" from close-by AM or SW broadcast stations
>THEN a preselector can do some good!

The receiver is simple and it cannot cope with the wideband noise.
Co-channel it can deal with.

Peter

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2002\06\30@174948 by Peter L. Peres

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On Sun, 30 Jun 2002, Roman Black wrote:

>That's a brilliant idea, using hysteresis so that
>the negative pulse is detected too. Just keeping on
>with the "minimum parts" idea I wonder if this could
>be implemented by adding a capacitor to the single
>transistor circuit, so the + pulse charges it and
>the - pulse discharges it. This might give good
>fractional response but will probably generate the
>occasional false pulse as the cap discharges after
>the thing stops turning.
>-Roman

The minimum schmitt circuit using transistors, uses two of those. Barring
some funky-doped mosfets which nobody has off the shelf. The other parts
amount to too many so use the cheap opamps. Goldstar GL358 should be cheap
enough for anybody I think. Remember that you need a schmitt with high
sensitivity. Therefore you want opamps. 2 Transistor schmitts can achieve
50mV hysteresis and lower but they are harder to set up and use more
parts.

>Peter L. Peres wrote:
>>
>> Roman, I did not consider that you would have to resolve single detents.
>> You are right about there being one detent where there are two (-) pulses.
>> I propose the following two solutions:
>>
>> 1. Use a Schmitt trigger on each input. The Schmitts will 'integrate' the
>> pularised pulses and produce normal quardature outputs (sin,cos, indigital

I meant polarised. My spell checker has been dead for weeks now. I guess
it shows ...

Peter

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