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Glen Pitt-Pladdy :: Blog

CCTV IR Illuminators on the cheap

Home CCTV can come in very handy at times, but without lighting even the best struggle. I've got a small set up with Zoneminder at home to keep watch on some trouble spots. I needed to monitor a driveway well away from the road (and lighting), but putting in floodlights seemed a bit over the top.

Lies in the dark

Many budget CCTV cameras make all sorts of claims about how good they are in the dark. Colour cameras are out if for night use (unless they are very expensive and mechanically remove the filter to switch to B&W in low light), and as any dubious activity is almost certain to be at night, best to stick with B&W cameras on a budget.

The spec of the ones that I am using claims they work down to 0.003 lux! The interesting thing is that when these £55 wonders are put next to a £1600 camera claiming 0.1 lux, the expensive one clearly does much better in the dark. I can't help but think that the specs are optimistic at best if not outright lies.

The next trick is that cheapie night cameras often add Infrared LEDs around them for illumination at night.  These cheapie B&W cameras actually work very well with Infrared, so perhaps not such a bad idea.....

The first thing that causes problems here is when the LEDs are behind the same glass/plastic cover - the camera simply sees reflections of the LEDs off the glass. Some cameras are a better and have separate glass covering the camera to avoid this.  Trouble is that it only takes a bit of mist, dust or a spider web and the high light intensity near the camera may still get reflected back and blind the camera.

As if that isn't enough, despite some more optimistic claims, some of these cameras have such short illumination ranges that they probably can't see anything more than a few meters away in total darkness.

Seeing the whole picture

Initially I tried to find some off-the-shelf IR illuminators.  The entry level units seem to cost even more than the cameras, and on closer inspection have a very narrow angle of illumination (many where around 15-30°). They definitely won't be much good to me.

I eventually found some wide angle LED units, but the price was completely out of the question for small home installations.

DIY

Being "skilled in the art" of electronic design (among many other things), building my own IR Illuminator is trivial, so why not?

Since building this should be relatively straight forward for anyone who is handy with a soldering iron, I'm putting this up for everyone, but I'm not going to provide any support. If you don't have the skills to safely build and test this from these rough guidelines then please don't try. If you wait a while then there will probably be a factory in China turning this design out by the million before long.  :-)

First I needed some decent IR LEDs. For CCTV, 850nm devices will give far more useful light than the common 940nm LEDs used for remote control and the like. 850nm LEDs are right on the edge of the visible spectrum and still give a faint visible red glow, but I'm not doing covert CCTV so no problem.

eBay came to the rescue and I got 20x 850nm 10mm LEDs with a 40° angle for £6.39 all in! The rest of the bits can normally be bought from any electronics hobby store of your choice.

Scribbled quick schematic:

IR Illuminator Schematic

This uses an LDR to turn the LEDs off during the day. I run them hot (high current) so this will probably improve their life significantly. I used an LDR which claimed something like 9K (not sure how it was measured), but there are probably many that will work if you change the value of the 100K resistor.  The key thing is that the transistors fully saturate and preferably do this rapidly as it gets dark.

I did try adding hysteresis, but with such low gain and no active pull-down it proved more hassle than it is worth, and the forward voltage of the LEDs keeps the BC337 at low voltage the moment there is any significant current through it so heat is not a problem.  Theoretically it should be possible to run many more LEDs off this without problems, especially if potted in resin.

I would suggest higher gain band transistors (BC337-40 and BC327-40). The BC337 handles minimal current and could have many different transistors substituted provided they have decent gain (BC547C, BC548C.... etc.)

I run the LEDs in 3 sets of 6 LEDs in series with a 68ohm resistor for each.  This is quite hot (higher current than normal) and they may not last long running like this. So far I've had months without problems.

For speed I grabbed a piece of Veroboard.  Ugly, but OK for a quick job with nothing sensitive or high frequency. This is a rough sketch of my layout with the copper strips running vertically and not all the LEDs shown:

IR Illuminator quick Veroboard layout

The 18 LEDs are set out in two groups of 3x3 with the LDR and switching circuit in the middle. X marks where tracks are cut. Ensure you avoid shorts between tracks. I don't know how well the typical CCTV power supply will handle them. I think it is also a good idea to test the build on a bench supply with a safe current limit until you know it is all working safely.

Since I have a wide area to cover and the LEDs are only 40°, I angled them outwards to give a bit of overlap between adjacent LEDs but cover a wide area. If you keep them straight then the coverage will be less but the overall light intensity far higher.

The final touch was to put them in a plastic box and pot them in resin for outdoor use.  I also put two M5 nuts in for mounting (putting tape over the back to prevent the resin getting into the threads).

I wired DC connectors on the lead so I could daisy chain this with the 12V camera supply:

Photo of finished Infrared Illuminator

Results

The illuminator is mounted high up at the top of a large Victorian house overlooking the driveway we are monitoring, and there still seems a decent amount of light for the cheapie cameras:

Before and after IR Illuminator

I'm happy with the results and it certainly is plenty of light for Zoneminder to do it's job.

Comments:

Skumar Image  25/11/2013 10:47 :: Skumar

Great Post. Just one doubt..I read in spec sheets of 850nm IR led that the Forward Current (mA) is 60mA Continuous, 120mA peak for 10% Pulse Width. Does the circuit involve any switching.. Thanks for taking the effort to help many of us..

Glen Pitt-Pladdy Image  25/11/2013 20:55 :: Glen Pitt-Pladdy

The only switching is day/night... not as in switching regulation/strobing. LEDs do vary a lot, both in forward voltage and maximum current. LEDs also tend to tolerate being run at higher currents, it just shortens their life. With my particular LEDs I'm getting about 1.5V forward drop x6 in series = 9V, about 1V drop on the transistor, leaving about 2V across the resistors - or about 30mA. That's more than their "recommend" operating current, but still gives them a decent long life. Check the specs for your LEDs and adjust the circuit accordingly.




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