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'[EE] Drive/Control Coil?'
2006\01\24@122926 by Padu

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Folks,

I'm lost here, I have a CCTV video lens that has a mechanized iris. The lens I'm using is the DC type (not the one that uses the video signal). It has 4 wires: Control (-), Control (+), Drive (+) and Drive (-).
The lens manual says that maximum voltage is 6V while 0.5V closes the iris and 4V opens the iris. I'm attaching a schematic cut from the lens manual if that helps.

My question is: how can I control that iris by myself? Yesterday I tryed plugging 5V to drive+ and GND to drive- and nothing happened (I added a current limiting resistor in series just in case).

Anyone have a clue on how to control this lens? If I have a 5V psu, just a pot is enough to control it?

Thanks

Padu

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2006\01\24@130458 by Lindy Mayfield

flavicon
face
You could have a bipolar stepper motor.  You'll certainly get much better information from others in this group, but I can send you a web link I've used in figuring out a motor I had.  It gives hints and things to try to figure out what sort of motor you have.

http://www.cs.uiowa.edu/~jones/step/types.html



{Original Message removed}

2006\01\24@132036 by Bob Axtell

face picon face
Yes, it is DRAWN like a bifilar stepping motor.

Look at ST L6219DSA as a good device to use
to drive it (available from Digikey).

--Bob



Lindy Mayfield wrote:

>You could have a bipolar stepper motor.  You'll certainly get much better information from others in this group, but I can send you a web link I've used in figuring out a motor I had.  It gives hints and things to try to figure out what sort of motor you have.
>
>http://www.cs.uiowa.edu/~jones/step/types.html
>
>
>  
>


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2006\01\24@132400 by olin piclist

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Padu wrote:
> My question is: how can I control that iris by myself? Yesterday I
> tryed plugging 5V to drive+ and GND to drive- and nothing happened (I
> added a current limiting resistor in series just in case).

Did you check that you still had nearly 5V after the current limiting
resistor?  Do you know what the max current is supposed to be?  How do you
know the limiting resistor wasn't way to big?


******************************************************************
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2006\01\24@134924 by Padu
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From: "Olin Lathrop"
> Padu wrote:
>> My question is: how can I control that iris by myself? Yesterday I
>> tryed plugging 5V to drive+ and GND to drive- and nothing happened (I
>> added a current limiting resistor in series just in case).
>

> Did you check that you still had nearly 5V after the current limiting
> resistor?

Yes, the whole time I had my DMM monitoring the voltage I was putting on the
motor.

> Do you know what the max current is supposed to be? How do you
> know the limiting resistor wasn't way to big?

I don't know. The lens datasheet only mentions max voltage. The datasheet is
the same for both dc-iris and the video auto iris type of lens. For the
video auto iris, it specifies a maximum 30mA. I used that value as a
reference and limited the current to 20mA, but in truth it's just a guess.

Somewhere I read a comment that "drive +/-" opens or closes the iris, while
"control +/-" brakes it. I also read that "applying voltage to drive opens
the iris", but it doesn't specify current ratings neither what the other set
of wires are for.

Cheers

Padu

2006\01\24@135134 by Padu

face picon face
From: "Bob Axtell"
> Yes, it is DRAWN like a bifilar stepping motor.
>
> Look at ST L6219DSA as a good device to use
> to drive it (available from Digikey).
>
> --Bob


If it was a stepper, then when I applied power to drive+ shouldn't it move
at least one step? Or perhaps the mechanism is too small that I couldn't
notice it?

Thanks for the reference though



Cheers

Padu

2006\01\24@140114 by Padu

face picon face
From: "Bob Axtell"
> Yes, it is DRAWN like a bifilar stepping motor.
>
> Look at ST L6219DSA as a good device to use
> to drive it (available from Digikey).
>
> --Bob

I quickly glanced the datasheet of the L6219DSA and saw these two features:

- OUTPUT CURRENT UP TO 750mA EACH WINDING
- WIDE VOLTAGERANGE 10V TO 46V

The first one I believe it's fine... if it's "UP TO" than I assume that it
is ok if the iris motor only uses 30mA right?

Now the second one is concerning, since the lens datasheet states a 6V max
voltage. Looking at some diagrams in the datasheet I could recognize the
dual coil drawing.

I wonder why they (the lens manufacturer) name the wires Drive +/- and
Control +/-?

Cheers

Padu

2006\01\24@140226 by David VanHorn

picon face
I could be wrong, but I thought these were current driven devices, as in
more current = less light, in a linear sense.

2006\01\24@143418 by Padu

face picon face
----- Original Message -----
From: "David VanHorn"
>I could be wrong, but I thought these were current driven devices, as in
> more current = less light, in a linear sense.

Well, one thing that I do know... less voltage = less light. Actually, the
iris only opens in the presence of voltage (as the datasheet says). When no
voltage is applied the iris is completely closed.

Cheers

Padu

2006\01\24@144138 by Spehro Pefhany

picon face
At 02:02 PM 1/24/2006 -0500, you wrote:
>I could be wrong, but I thought these were current driven devices, as in
>more current = less light, in a linear sense.

Should be more current-> more light so that the iris mostly closes
with power off.

I think the drive is to drive the iris open, and the cont coil has
to do with damping. It's possible it's a velocity output for the
control circuitry.

Are you (the OP) sure that applying a few volts with the correct polarity
(slowly) to the "drive" terminals doesn't open the iris?

This seems to be one of those irritating things where there are quite
a few manufacturers of compatible lenses and compatible cameras, but
little available on the net in the way of documentation of the interface. 8-(

Some of the threads used on cameras are similarly obscure, IIRC.

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
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2006\01\24@150114 by David VanHorn

picon face
>
> Should be more current-> more light so that the iris mostly closes
> with power off.


That's right.. I hadn't messed with one in a while.
Off is closed to protect the sensor/curtains.

2006\01\24@151654 by Padu

face picon face
From: "Spehro Pefhany"
> Should be more current-> more light so that the iris mostly closes
> with power off.

That is correct

> I think the drive is to drive the iris open, and the cont coil has
> to do with damping. It's possible it's a velocity output for the
> control circuitry.

Yes, actually, for other lens models they replace the name "control" by
"damping", could you elaborate more on this subject?


> Are you (the OP) sure that applying a few volts with the correct polarity
> (slowly) to the "drive" terminals doesn't open the iris?

Well, it was 11pm and I had 3 shots of bourbon 8^D

I was using a current limiting (30mA) resistor and a pot to give me a
certain voltage. I thought that opening or closing was done by varying the
drive voltage.

Do you think that if I apply a constant 4V to drive + and GND to drive - it
will keep opening the iris while voltage is applied? According to the lens
datasheet, the drive winding has an internal resistance of 190 ohms. Does
that mean that I don't need a current limiting resistor and I can plug the
5V directly from my psu?

> This seems to be one of those irritating things where there are quite
> a few manufacturers of compatible lenses and compatible cameras, but
> little available on the net in the way of documentation of the interface.
> 8-(
>
> Some of the threads used on cameras are similarly obscure, IIRC.

This is one of those things that don't generate millions of hits on google.
Some time ago I was trying to get a female jack for that 4 pin plug, I
simply gave up.

Cheers

Padu

2006\01\24@181714 by Spehro Pefhany

picon face
At 12:16 PM 1/24/2006 -0800, you wrote:
>From: "Spehro Pefhany"
> > Should be more current-> more light so that the iris mostly closes
> > with power off.
>
>That is correct
>
> > I think the drive is to drive the iris open, and the cont coil has
> > to do with damping. It's possible it's a velocity output for the
> > control circuitry.
>
>Yes, actually, for other lens models they replace the name "control" by
>"damping", could you elaborate more on this subject?

No, as I know virtually nothing about it with 100% certainty. I don't even
have a lens in front of me, as you do. But I can visualize how the guts
*could* work.

> > Are you (the OP) sure that applying a few volts with the correct polarity
> > (slowly) to the "drive" terminals doesn't open the iris?
>
>Well, it was 11pm and I had 3 shots of bourbon 8^D

Might be worth trying again. Sober or not is up to you.

>I was using a current limiting (30mA) resistor and a pot to give me a
>certain voltage. I thought that opening or closing was done by varying the
>drive voltage.

The voltage across the coil (actually, the current through it) most likely
is what matters.

>Do you think that if I apply a constant 4V to drive + and GND to drive - it
>will keep opening the iris while voltage is applied?

I really don't know. It could work either way, with the lens integrating
the signal from the camera, but I suspect it acts more like a galvo with
the iris 'positioned' according to the current. You'll soon see what it
really does, and hopefully tell us.

You don't happen to have a full schematic of a compatible camera do you?

>According to the lens
>datasheet, the drive winding has an internal resistance of 190 ohms. Does
>that mean that I don't need a current limiting resistor and I can plug the
>5V directly from my psu?

Yes, but I'd measure the resistance first and raise the voltage slowly and
with the correct polarity.

{Quote hidden}

It may be possible to find it online, but only if you already know what
to look for. I'd go to my paper library of obscure and exotic Asian parts.
But only for a large quantity buy-- too much $$ work otherwise.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2006\01\25@031029 by Robert Rolf

picon face
DC controlled camera lenses are basically milliampmeters.

A mechanism similar to a meter movement opens the iris against
a closing spring force. The 'drive' is a variable CURRENT to
make the circuitry simple and not dependent on absolute coil resistance.
And the magnetic force is a function of CURRENT since the coil is
quite inductive.
The 'control' winding is used as velocity feedback to damp the
coil motion, by reducing the drive current as the iris moves, to
prevent overshoot.

You can dive the lens using a variable voltage source with a current limiting
resistor into the 'drive' terminals.
Hang a scope on the 'control' leads to see the back EMF the moving coil
generates. If you short out the control winding you get maximum damping,
which is probably what you want for your basic voltage control.

Robert


2006\01\25@124229 by Peter

picon face


On Tue, 24 Jan 2006, Padu wrote:

{Quote hidden}

The iris is meant to be operated in closed circuit with AGC signal. You
want to operate it open circuit, so you can drive it with a control
current. Try a constant current generator with a LM317L and a
potentiometer. The action will be sticky and not linear. You want the
maximum set current to be about 30mA.

Peter

2006\01\25@124429 by Peter

picon face


On Tue, 24 Jan 2006, Bob Axtell wrote:

> Yes, it is DRAWN like a bifilar stepping motor.
>
> Look at ST L6219DSA as a good device to use
> to drive it (available from Digikey).

Please no. It is not a stepper motor. It is a galvanometer (d'Arsonval)
with a feedback coil used to electronically dampen its movement.

Peter

2006\01\25@125416 by Padu

face picon face
"Robert Rolf" wrote
{Quote hidden}

That makes sense. I'll do a couple more tests tonight.

So, if I want to make a control circuit that simulates a manual iris and its
f-stops (supposing that I have a way to calibrate an actual iris aperture to
an f-stop), I'd have to use the control as feedback right? As you can tell
I'm a newbie with electronics, so what should I use for that, an opamp?

Thanks a lot!

Padu

2006\01\25@125438 by Peter

picon face

On Tue, 24 Jan 2006, Olin Lathrop wrote:

> Padu wrote:
>> My question is: how can I control that iris by myself? Yesterday I
>> tryed plugging 5V to drive+ and GND to drive- and nothing happened (I
>> added a current limiting resistor in series just in case).
>
> Did you check that you still had nearly 5V after the current limiting
> resistor?  Do you know what the max current is supposed to be?  How do you
> know the limiting resistor wasn't way to big?

These irises will stick if overdriven. Knocking it lightly will release
it if stuck. The drive polarity is important. Connecting it straight to
5V should cause no damage (26mA through the 190 Ohm coil). A single 1.5V
battery is a safer thing to try to determine the polarity. Attach it
first one way then the other and see which opens the lens a little.
Mark this wire (only feed current to the 190 Ohm coil, ignore the 540
Ohm feedback coil for now). Then make a constant current generator with
a LM317L and a potentiometer for 30mA f.s. and connect it into the
circuit (observe the polarity you found before with the 1.5V battery).
You will need a 9V battery to drive the LM317+iris coil assembly. You
should be able to set the iris with the potentiometer. Afair you have to
use a 10kOhm pot in series with 1 KOhm fixed resistor to set a LM317L
between 3 and 30mA.

Peter

2006\01\25@130110 by Peter

picon face

On Tue, 24 Jan 2006, Padu wrote:

> I wonder why they (the lens manufacturer) name the wires Drive +/- and
> Control +/-?

Because one of them is used to drive the permanent magnet in the rotor
and the other is used to dampen (or control) the movement by generating
a speed-proportional feedback voltage.

Peter

2006\01\25@130218 by Peter

picon face


On Tue, 24 Jan 2006, David VanHorn wrote:

> I could be wrong, but I thought these were current driven devices, as in
> more current = less light, in a linear sense.

More current = more light. The drive coil will spin the rotor magnet
against a (weak) spring. It works exactly like an analog meter except it
is moving magnet not moving coil, and it has a feedback winding.

Peter

2006\01\25@130720 by Padu

face picon face
"Spehro Pefhany" wrote
>>Yes, actually, for other lens models they replace the name "control" by
>>"damping", could you elaborate more on this subject?
>
> No, as I know virtually nothing about it with 100% certainty. I don't even
> have a lens in front of me, as you do. But I can visualize how the guts
> *could* work.

I was just asking what prompted you to use the word damping and how you
thought it worked, but Robert Rolf's post gave a good insight on what
damping means.


>>Well, it was 11pm and I had 3 shots of bourbon 8^D
>
> Might be worth trying again. Sober or not is up to you.

Who said I wasn't sober 8^D  The problem I believe is that I was sleepy


> The voltage across the coil (actually, the current through it) most likely
> is what matters.

That is correct. Yesterday I plugged the psu (5V) directly to the drive coil
and it fully opened. As expected, the current going through the coil was
about 25mA.
I was using a pot to reduce the voltage and the resistance of the pot was
way too high (5 meg), so when I measured the voltage coming out of the pot,
I could measure 3.5V, but as soon as I plugged it to the coil, it dropped to
0V.


> I really don't know. It could work either way, with the lens integrating
> the signal from the camera, but I suspect it acts more like a galvo with
> the iris 'positioned' according to the current. You'll soon see what it
> really does, and hopefully tell us.

I don't know what a galvo is, but if there is enough current for the coil,
then applying positive voltage to drive+, it does open. But that's only half
of the problem, well, a third really. Now I have to find out how to create a
"black box" that inputs f-stops and outputs analog signal to implement a
corresponding aperture on the lens.


> You don't happen to have a full schematic of a compatible camera do you?

No. I'm monitoring ebay to see if I can find a really cheap (broken is fine)
compatible camera that I can cannibalize (for the mating plug).


Cheers

Padu

2006\01\25@131617 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: .....piclist-bouncesKILLspamspam.....mit.edu [EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu]
>Sent: 25 January 2006 18:02
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Drive/Control Coil?
>
>
>
>
>On Tue, 24 Jan 2006, David VanHorn wrote:
>
>> I could be wrong, but I thought these were current driven
>devices, as
>> in more current = less light, in a linear sense.
>
>More current = more light. The drive coil will spin the rotor magnet
>against a (weak) spring. It works exactly like an analog meter
>except it
>is moving magnet not moving coil, and it has a feedback winding.

Bearing in mind that these coils are normaly driven in a closed loop from the video output amplitude, I have to wonder how repeatable the mechanism would be from just applying fixed currents.  Any stiction will give some hysteresis in the transfer function, which could make getting a repeatable aperture setting a little tricky.

Regards

Mike

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2006\01\25@132526 by Padu

face picon face
"Peter" Wrote
> These irises will stick if overdriven. Knocking it lightly will release
> it if stuck. The drive polarity is important. Connecting it straight to
> 5V should cause no damage (26mA through the 190 Ohm coil). A single 1.5V
> battery is a safer thing to try to determine the polarity. Attach it
> first one way then the other and see which opens the lens a little.
> Mark this wire (only feed current to the 190 Ohm coil, ignore the 540
> Ohm feedback coil for now).

I found it, but when I apply 5V (25mA) to it, it fully opens really fast.

> Then make a constant current generator with
> a LM317L and a potentiometer for 30mA f.s. and connect it into the
> circuit (observe the polarity you found before with the 1.5V battery).
> You will need a 9V battery to drive the LM317+iris coil assembly. You
> should be able to set the iris with the potentiometer. Afair you have to
> use a 10kOhm pot in series with 1 KOhm fixed resistor to set a LM317L
> between 3 and 30mA.

And how do I use the feedback from control wires?
I'll try your suggestion tonight (if Radioshack has LM317's) or whenever I
get the part from mouser.

Thanks a bunch!

Padu

2006\01\25@194238 by Robert Rolf

picon face
Michael Rigby-Jones wrote:
>>More current = more light. The drive coil will spin the rotor magnet
>>against a (weak) spring. It works exactly like an analog meter
>>except it
>>is moving magnet not moving coil, and it has a feedback winding.


>Bearing in mind that these coils are normaly driven in a
>closed loop from the video output amplitude, I have to
>wonder how repeatable the mechanism would be from just
>applying fixed currents.  Any stiction will give some hysteresis
>in the transfer function, which could make getting a repeatable
>aperture setting a little tricky.

They are very repeatable. The way stickion is tackled is to
have a 'buzz' on the control current, about 60H at 10% amplitude
should do.

And if he wants specific apertures (never done in reality since
all we really care about is getting a nominal video output level),
he should approach the desired setting from the same direction each
time. e.g. always open the lens toward the f stop you want.

Robert

2006\01\26@123821 by Peter

picon face

On Wed, 25 Jan 2006, Padu wrote:

{Quote hidden}

You don't use the feedback coil. It has nothing to do with position, it
is a speed proportional voltage. In irises meant to be used as you wish
there is an additional sensor (usually linear Hall or GMR) that gives a
voltage proportional to the iris position. Yours hasn't got that so the
best you can hope for is to use a potentiometer roughly graduated in F
stops and live with the stiction when you make small changes.

Peter

2006\01\26@134429 by Padu

face picon face
"Peter" wrote
>> And how do I use the feedback from control wires?
>> I'll try your suggestion tonight (if Radioshack has LM317's) or whenever
>> I
>> get the part from mouser.
>
> You don't use the feedback coil. It has nothing to do with position, it
> is a speed proportional voltage. In irises meant to be used as you wish
> there is an additional sensor (usually linear Hall or GMR) that gives a
> voltage proportional to the iris position. Yours hasn't got that so the
> best you can hope for is to use a potentiometer roughly graduated in F
> stops and live with the stiction when you make small changes.
>
> Peter

I get it now. Looking at the control wires on the oscope, when I apply
voltage to the drive wires the iris opens and I can see a very brief spike
on the control wires, but after that it returns to 0V again. I tried
shorting the two control wires, but it didn't change anything, the iris
opens at the same speed.

I also tried applying 1.2V to the lens (AA battery), didn't open, but 2.4V
did open it, but in the same position and speed 5V did, so should I use the
LM317 and a pot to control the output current instead? Well, I guess I'll
find that out when my LM317 arrives won't I? 8^)

Thanks for your help!

Padu

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