Problem Statement: How to design "DC iris control" circuitry for CCTV camera applications?
I have a proprietary and old 'Tamron' lens with me, I wish to control its IRIS. The iris control of the lens has 8 pins.
4 pins of motor driving and control: drive + and -, damping + and -, with coil resistance 120 ohm each.
4 pins of positional feedback element Hall sensor: bias+ and -, hall + and -. The bias current of Hall sensor is 1 mA typical and 5 mA maximum.
Neither the manufacturer is ready to help with reference design to control the iris, nor his datasheet speaks much on control part (the data is partly Japanese and partly English, with great struggle I deciphered above info.)
Survey done so far:
I have seen custom ICs like LC898201 which say they do the job of IRIS control but I could not find any solid application note explaining how does they do it, moreover these ICs have high MOQ problems to use in my design.
Also I have searched through out internet on different forums for any references, barely I could find below schematic. I am not sure whether its a DC-iris control, it takes video input to fix threshold i think, on the other-side tries to tweak some AGC controls.
My naive understanding:
Primarily, one can design a PWM based control for driving the iris via drive+/- pins and take damp+/- for feedback through an op-amp to provide it as a correction to drive+/-, as done in above reference, and using the Hall sensor feedback to control the iris position.
Provided, all this control need to done seeing the histogram of collected image.
Kindly throw your views or references of schematics which are used in CCTV applications to control the iris of an lens.