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Infrared Illuminator for CCTV

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mikky

New Member
I have an old CCTV camera at the front of my house. At night, the camera doesn't pick up much detail, so I'm building an infrared illumator which I'm planning to house in an old halogen security/work light so it 'blends in' a little.

I don't know whether to go for:

1. 150+ LEDs, powered at 1.5V/30mA directly by DC (with protection resistors); or
2. 30-40 LEDs, pulsed to a higher current (1A) for 10ms (or so) using a 555 timer and transistor.

By all accounts, pulsing the LEDs to a higher current makes them much brighter, and uses less energy (as it doesn't operate continuously), at the expense of a few additional components and the chances of them burning out faster. More straight DC powered LEDs mean I can angle the LEDs in the housing to create a wider viewing angle, and they'll not be as 'visible' (i.e. glowing red at night).

Space isn't a factor (6"x4" / 150mm x 100mm), but current requirement and overall energy useage is. I have a 12V / 2A power supply which I'm planning to use, and for efficiency I'd like to use the minimum amount of energy, with the maximum amount of illumination.

Planning on using LEDs bought on ebay from China to complete the project. "may139189" picture labelled "Asia Engineer" - says 60mA operating current. Good idea/bad idea?

Is pulsing worth it, and how many LEDs can I get away with using either option based on my 2A supply?

TIA!
Mikky
 

Reloadron

Well-Known Member
Most Helpful Member
Before you worry about IR illumination you are absolutely sure the closed circuit television camera you have uses a sensor that detects IR illumination? Additionally you may want to consider the frame rate of the camera before pulsing the LEDs.

Ron
 

mikky

New Member
Yep, I'm sure it detects IR - It's a webcam which I removed the IR filter on for exactly this purpose, and checked using a TV remote as a 'light' source. The frame rate of the camera is 15-30fps depending on the resolution, and drops to around 2-3fps in low light.

Mikky
 

Reloadron

Well-Known Member
Most Helpful Member
Given a choice I would likely go with strings of 6 EA of the 1.5 volt 30 mA flavor running them at about 20 mA so you get 12 volts - 9 volts / 20 mA = 150 Ohms. I would just add strings as required till I got the desired illumination. Yes, you could drive a mosfet using a 555 but I wouldn't bother. Others may have more suggestions but that is about what I would do.

Ron
 

mikky

New Member
Thanks for the advice!

I've noticed that the latest CCTV cameras don't use the pulse circuit, but I'm not sure if that's because modern IR LEDs have a higher output than the older ones, or because there's just more to go wrong, or it costs more to make?

Just to check, if I use strings of 6 at 20 mA, each chain will draw 120mA, so I can effectively run 16 chains (1.92A) in parallel from my 2A supply?

If I wanted to be able to dim this thing, would I be better building the PWM circuit rather than use a potentiometer on the supply?
 

Reloadron

Well-Known Member
Most Helpful Member
Nope, doesn't work that way. If I string 6 LEDs in series as I mentioned using a 150 ohm resistor the current in the string will be 20 mA. Therefore for each successive string I would add 20 mA. Ten strings of 6 LEDs using a 150 Ohm current limiting resistor would draw about 200 mA or .2 amp at 12 volts which is .2 X 12 or about 2.4 watts.

<EDIT> That is one current limiting resistor per string. :) </EDIT>

Ron
 
Last edited:

mikky

New Member
Ahhhhh I don't know what I was thinking there. 20mA per chain is perfect - I can parallel quite a few then before I start having to worry about the power requirement.

Was considering a dimming circuit in case the illuminator was bright enough to guide down aircraft onto my driveway, but if it's only a few watts, I can happily live with that.

Thanks for all your help Ron!
 

Reloadron

Well-Known Member
Most Helpful Member
My Pleasure. :)

Ron
 

Ross Craney

New Member
Rather than using 150 leds as a single light you may consider having 3 lights of 50 leds spaced accordingly around the subject area. If you imagine a car park lit with one big floodlight as against multiple lights you will understand the result. Unless the area is "flood" lit as against "spot" the iris will close because of the over exposure in the hot spot of the IR lighting , resulting in under exposure ( ie darkness) around the perimeter. A good even spread of the IR light is what you need for good results.
 

mikky

New Member
Ross,

Was thinking about spreading the IR sources out just as you suggested, but from with the distance and angle I need to cover, a single source will work well. It's going to be mounted on the corner of my house, looking along the side of the house as well as covering the driveway. I'll angle the LEDs as I move across the illuminator to ensure the illumation is more diffused, which should hopefully prevent the hotspot phenomenon you described.
 

ronsimpson

Well-Known Member
Most Helpful Member
The hot spot also comes form the "angle" of radiation for the LEDs. I have used IR LEDs with angles of 6 to 180 degrees. The 6 degree will make hot spots it lights only a small spot in the picture. The 180 will not. I like trying to match the angle the camera sees.
 
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