DC Iris Control Circuit

[_neoRAGE_ 0]

Hi,

I was wondering if anyone knows how i can go about making a DC iris control circuit, assuming i can provide (for example) 0-3.3V as an input which causes the iris to go from 0%-100% open?

 

I note that many of the lenses supporting DC/Auto-iris have a 4 pin connector with signals DRIVE+, DRIVE-, BRAKE+, BRAKE-; how do i drive these? I tried finding information online but i was shocked to see there was none there!

 

The lens i am trying to drive is a Computar HG2Z0414FC-MP.

 

Any help would be really really appreciated

 

_neoRAGE_

[Kiwi 0]

I have tried to design the opposite circuit - to operate a manual motor-driven iris from the camera's DC signal. The lens is a Computar 8-80 that I picked up cheap since it was lacking the DC iris. It didn't work as the motor couldn't move the iris fast enough to respond before the camera integrated the error to the maximum value. You are correct - there is almost no technical information or standards available for this fairly common device.

 

What you are trying to do won't work either as there is no positional feedback from the DC iris to tell you when you have matched the voltage demand. The camera knows this instantly by the resulting exposure level.

 

The DC iris has two coils, one to move the iris and the other to provide velocity feedback. The moving part of the iris has a magnet and is normally held closed by a light spring. The driving coil opens the iris against the spring somewhat proportional to current supplied, while the other generates a small current proportional to the iris velocity.

 

If you apply 0 - 30 mA to the drive connections you can open the iris, however you will find it very hard if not impossible to obtain any stable intermediate position. With a suitable series resistor to supply the minimum required current you can leave it fully open permanently.

 

Have fun!

[_neoRAGE_ 0]

Hmm...i still don't fully understand the function of the dampling/ brake/control coil - is it an output or am i suppose to drive that somehow?

 

thanks in advance.

 

_neoRAGE_

[Kiwi 0]

It's an output and a very low-current one at that. It provides feedback to the driving circuit as to the effectiveness of the driving current at moving the iris. The term "brake" which we often see used is not an accurate description of the function.

[_neoRAGE_ 0]

Oh i see, so does someone have an idea of how i could drive this baby which has both Drive and Damp coils?

 

Please help...

 

_neoRAGE_

[darrellm 0]

here is my take, totally untested.

 

consider the drive and brake coils as two coils of a stepper motor and the iris control lever as

a rotor.

 

I assume the iris will be positioned to the proportion of currents between drive and brake coils...

with spring tension to close without power.

[hardwired 0]

you might try this one from Pelco http://www.global-download.schneider-electric.com/852575770039EC5E/All/DF45FED8CFDF047185257633005BBCC0/$File/c784.pdf

 

That lets you use a DC lens on a video drive camera, which has a variable DC output for lens control.

[manf 0]

I've been trying to find an answer to the same problem: How do you design a circuit to control an DC Auto-Iris lens?

 

Previous answers in the post are interesting, but don't give specific information about how to go about designing an interface. Does anybody have a spec or application/design note or whatever other information about how to do this?

 

Thanks for any feedback!!!

[OMD 0]

I am in the same boat. I have a DC Drive lens that I would like to power to fully open. I have the full pin config for the lens. The lens says it has a current consumption of 22mA（Max.）at 4V DC . Any ideas? If any of the previous posters have sorted it I would love to know how.

[joost 0]

I found an example circuit in this pdf file:

http://www.produktinfo.conrad.com/datenblaetter/175000-199999/191004-sp-01-en-CCD_Farbkamera_m_Zoom_hochaufloesend.pdf

 

What I figured out so far is this.

A signal from 0-4V drives the iris open against a spring.

An opamp circuit integrates the difference between lightlevel and setpoint and uses the output as the DRIVE signal.

This would drive the iris to keep the light level constant, but there is a catch.

The mechanical iris has static friction. When the driving force overcomes the friction, the iris would suddenly jump and overshoot the setpoint. It would continuously jump around the setpoint if not compensated.

The break coil provides an inductive feedback signal when the iris jumps, so the drive circuit can break/dampen the output to avoid overshoot.

 

The feedback circuit does not allow you to simply put the iris in some fixed position. This is why some manufacturers now use a servo type iris on their cameras.

 

But there may be another approach. I have not tried it, but I think it may work.

Suppose you connect the DRIVE directly to the 5V PWM output of a microcontroller. By carefully choosing the PWM frequency, you can make the iris blades vibrate, removing the static friction while you vary the position by changing the duty cycle.

To reduce wear and audible sound, you could switch to a much higher frequency with the same duty cycle once the iris is in position.

If anyone tried this, please let us know if it works!

[bhamadicharef 0]

Hi all

 

Any hints on this DC Iris control circuit. I have found a old

Kenko optics and it also has this 4 pins connector. I would

be interesting to learn more about how to drive it ...

 

When I recently asked from kenko-tokina I typically get a link to

http://www.tokina.co.jp/en/security/TVR2713DCIR%20Spec.pdf

 

but no real example of eletronic circuit.

 

Dr Brahim HAMADICHAREF

Singapore

[tamasflex 0]

Hi

I have the same problem as Mr. NeoRAGEx.

I have a camcorder lens Fisher and I have not found a simple circuit to control the iris .

I read with interest the comment but do not see a practical scheme.

If you have a diagram please publish.

I want to use the lens from a CCTV camera JVC TK-C1380.

Servo motors can control but I still have problems with the iris.

Thank you.

[wonlife0809 0]

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[tamasflex 0]

front door security camera, easy to install, no wire, lithium - ion battery, IR night version, GSM function, auto alarm, auto photo shoot, video message, please visit: www.ekeatech.com.

 

 

wonlife 0809, now advertise for free?

I think you have an answer to my question!

[joost 0]

But there may be another approach. I have not tried it, but I think it may work.

Suppose you connect the DRIVE directly to the 5V PWM output of a microcontroller. By carefully choosing the PWM frequency, you can make the iris blades vibrate, removing the static friction while you vary the position by changing the duty cycle.

To reduce wear and audible sound, you could switch to a much higher frequency with the same duty cycle once the iris is in position.

If anyone tried this, please let us know if it works!

I tried it using a function generator so I could vary frequency, duty cycle and amplitude. Unfortunately it did not work. Static friction was reduced, but the forces a such that it only has two stable positions: completely closed or full open.

If you want it fully open, just apply 5V to the drive coil, but any intermediate position does require some sort of position feedback, which is normally the camera's exposure level.

 

It may just be possible to derive a position signal by measuring the inductance of one of the coils, but this will be a complex circuit for which I have no time or need to develop.

[tamasflex 0]

Gentlemen

Where can I get the circuit diagram of cameras Grundig FA 43 and FA 73 ?