DC Auto-Iris control for CCTV lens

Hi,

I am looking to build a circuit to control the iris of a cctv lens. The input of that lens is a DC auto-iris type which is: pin 1: Damping- , pin2 Dampining+, pin3 Drive+, Pin4 Drive-. Here is a link on how dc auto-iris work http://www.gevicam.com/images/ED-_TN-07001AI_lens.pdf I can make a circuit to control the iris manually but it is not practical adjust it for all lighting conditions. Generally, CCTV uses the output of the video signal to adjust the iris opening size. How do I go about building such circuit for auto-light balancing?

This is part of my other project to use Arduino to control a manual zoom lens. I know how I can attach and control the zoom with servos but the iris part seems to cause me problems.

Anyone?

Simulate a sync-less video signal with PWM and a low-pass filter?

Generating a pwm will be to control the opening and close of iris but I want it to automatically responce to the brightness of the video signal, like too bright then close the iris more etc

I can send the video signal through a low-pass filter cut off at around 2MHz-2.5Mhz to extract the lumanace signal and using that to feed to the control mechanism. It is that control machanism that I want to know how to use the camping signal to feedback to the drive signal.

The problem is that the camera will have some AGC (automatic gain control) that will mess up control. Maybe a peak detector feeding into the analogue input would work. Then just use a nudge loop to control the iris.

It is a simple board camera and I doubt it has AGC. What do you mean by nudge loop?

It will be the first video circuit I have seen without AGC.

A nudge loop is one where you look at the input and decide if it is larger than or smaller than the required value, and then nudge (change the output value (iris size) ) in the appropriate direction. Repeat it often enough and it converges on the correct setting.

Just checked camera spec, it has AGC, damn it.

2 Ideas:

  1. Use an electronic light measuring method (like http://www.sparkfun.com/products/8940 or http://www.sparkfun.com/products/8688) and use the Arduino to adjust the iris of the camera in relation to the measured ambient light.

  2. Use an Elphel camera ( http://www3.elphel.com ) and interface it with the Arduino (like http://wiki.elphel.com/index.php?title=Arduino ). That way you have full histogram access and can adjust the iris accordingly.

Hello kkman20xx,

You said: "I can make a circuit to control the iris manually"

I' like to make a circuit just like that. Would you please share the corresponding circuit diagram?

Regarding your original question, I found this paper: http://ecad.tu-sofia.bg/et/2005/pdf/Paper101-T_Djamiykov1.pdf. If you write them, they might help you. Thanks and good luck!

did u finish ur project. i also have to do the same. pls share informations

I am also working on the same project. Please share the project details at rajatece@hotmail.com

Hi!

I'm trying to do more or less the same but with other lens. Without light sensor.

I've found this: http://www.produktinfo.conrad.com/datenblaetter/175000-199999/191004-sp-01-en-CCD_Farbkamera_m_Zoom_hochaufloesend.pdf in another post. There are the iris signals in the sheet 4, but I don't know how to adapt it to my project (I can't use any light sensor, I just need to open the IRIS always in the same %).

I've tried joining both ' coil -' with ground and 'control coil+' to a 0.1uF capacitor (bypased to ground) and to the negative input of a comparator. The positive input is connected to a voltage divider. And the output is connected to a base of a BJT. The collector of the BJT is joined to 3.3 V and the emiter connected directly to the 'drive coil+'. When the positive inpout of the comparator rises up 45 mV the iris opens slowly. I can adjust to mantain the iris semi-opened but it is not repetitive.

Can somebody give me any idea or share how to do it? Thank you! PD: You can find me at: lo.roquetes@gmail.com

If someone can do this, can u mail goxelbey_67@hotmail.com It can be any type of circuit with or without IC’s. Thanks.