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Topic: DC Iris Control Circuit Help (Read 1 time) previous topic - next topic

WaxFlywheel

Sep 07, 2013, 09:47 pm Last Edit: Sep 07, 2013, 09:48 pm by WaxFlywheel Reason: 1
Hello everyone,

I have a small lens that has a dc-iris.
From what I have gather, the four wires are:
+ drive
- drive
+ damp
- damp
(reference link image)

There is another post in these forums talking about this... yet nobody was successful in making it work.

I did find what I think might help us out, and it's a YouTube video that shows a guy controlling a dc-iris off a cctv lens, using a small circuit and a POT.
Now, this circuit is flying over my head... so I was wondering if you could help me out to figure it out.
The YouTube video is called DC Iris Driver Circuit Mockup
DC Iris Driver Circuit Mockup.

Here is a screen-shot I took off the video... which isn't much high quality, yet I think it's the best I could come up with.


Any idea what I need to replicate this circuit?
I'm a n00b, yet I can try and draw it up in Fritzing!

Thank you!!
The best way to predict the future is to create it !!!

dc42

My guess is that the drive pins are connected to a small dc motor and you need to drive them them from a small h-bridge. What is the resistance between those pins? The other pins are possibly connected to a sensor that detects the rate of movement. The diagram suggests that they could be connected to an amplifier.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

WaxFlywheel

Hey dc!

Thanks for replying!
The "damp" ones, I have seen in other places on the net, that it's a "dampner".

Apparently, if one applies +/-, the drive moves too fast.
So you also have to apply a dampening current.

Maybe I'm way off base with that.

I will measure the resistance now and post back in a couple of minutes!
The best way to predict the future is to create it !!!

WaxFlywheel

Ok, here's the data...
The wires are red, black, white, and green.

I only have a reading from:
red to green: 186 ohms
white to black: 879 ohms



Anything you guys can suggest I try over here?
I just don't know where to even start.

Thank you!
The best way to predict the future is to create it !!!

dc42

I assume red and green are the drive connections. Try connecting them to a pair of pwm output pins. From each pin also connect a Schottky diode to ground (anode to ground) and another to +5v (cathode to +5v). Type BAT43 or BAT85 would be suitable. Drive the first output low and pwm the other. To adjust the iris the other way, drive the second pin low and pwm the first.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

WaxFlywheel

Hello again!
I ordered the Schottky diodes (BAT43 and BAT85).

I am awaiting on them to arrive.

===
As a side note, I connected the cables in pairs to a AA battery, and the iris opened fully when energized.
Closed fully when disconnected.

So I did:
red+white -- AA positive +
green+black -- AA negative -

===
Not sure if that additional information can help somewhat!
The best way to predict the future is to create it !!!

dc42

If the iris behaves as you have just described, then you should only need to drive it from one Arduino pin, not 2. Connect red to the digital output pin, and green to ground. Also connect a Schottky diode between the output pin and +5V, cathode to +5V. Leave white and black disconnected.

As 1.5V appears to be sufficient to operate the iris, I further suggest that you connect a series resistor of about 330 ohms between the digital output pin and the red wire, to avoid overdriving the iris.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

WaxFlywheel

Hello dc42!!

Thanks for your reply!
I will do those as soon as the Schottky diodes arrive (ordered from eBay China, and ordered from DigiKey... I'm in the USA, so lets see if DikiKey arrives soon!).

When they arrive, I will setup what you say, and report back.

===========
Thank you!
The best way to predict the future is to create it !!!

WaxFlywheel

#8
Sep 18, 2013, 02:50 am Last Edit: Sep 18, 2013, 02:56 am by WaxFlywheel Reason: 1
Hello again everyone,

I'm kind of at a loss as to what to do next.

dc42, I tried to visualize your suggested circuit, yet I'm having a hard time even starting with anything.
I just don't have the experience.

Can you give me a little bit more hints?

===
Another option/possibility I think I stumbled across is a "resistor ladder".
I do have a bunch of resistors, and I bought an "opamp".

Any idea how I could go about this?

Thank you for your time and help!


EDIT:::::
I thought of using a circuit like the one mentioned on this page.
I do have the RFP30N06LE MOSFET... yet I believe it needs at least 7.0v to "activate" or do something.
So I can't see how to do that.

Although it's doing pretty much what I need (see the video at the bottom of that post).

The best way to predict the future is to create it !!!

dc42

The mosfet circuit would work, but you don't need it because the current draw of the iris is so low. See attached schematics. The left hand one is my original suggestion, based on the assumption that you needed to apply power one way to open the iris and the other way to close it. The right hand one is my later suggestion, based on your observation that the iris is fully open when energized with 1.5V and fully closed when not energized. I suggest you use one of the PWM pins that is not attached to timer 0 (so not D5 or D6 on a Uno), because I expect you will need to increase the PWM frequency.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Hi, have you completed you project. I am also trying to decode the circuit for controlling dc iris through a pot so that i can further interface it with arduino. Please share information at rajatece@hotmail.com.
Rajat Sharma

WaxFlywheel

#11
Mar 19, 2014, 03:23 am Last Edit: Mar 19, 2014, 03:35 am by WaxFlywheel Reason: 1
The best way to predict the future is to create it !!!

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