Archive for February, 2011

night vision basics

Night vision is one of the most important factors when considering any kind of video operated spy gadget as this technology allows the viewer to see in complete darkness while the subject is completely unaware. Because infrared light (radiation) falls just below red on the visible light spectrum, making up the wavelengths from about 750 nanometers to about 1500 nanometers, this light cannot be seen by human eyes, but it can easily be seen by many video cameras, making it useful as a covert lighting method in night vision systems.

Read more: Invisible Light Basics DIY tutorial.

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Figure 0 - This external controller allows any device to control the shutter release
This external controller allows any device to control the shutter release

There are times when you need to acquire a very high resolution image, triggered by some external event such as movement, time, or computer control. Video security cameras are very limited in resolution, often to less than 640 x 480 pixels, which in digital camera terms is less than half of one megapixel.

Nowadays, a small digital camera that can take an image with a resolution of 4000 x 3000 pixels can be purchased for mere pocket change, so even if your subject is a long distance from the camera, the details will still be present in the image when zoomed on a computer screen. This simple project demonstrates how to hack into the camera’s shutter release button to add some kind of external control to allow automated picture taking.

Because this project is a hardware hack, you should not try this with a good camera, or one that you are worried about breaking. There is always a possibility of destruction when cracking the case open on such a small electronic device that is jammed full of tiny components. Of course, if you are good with small tools and a soldering iron, then this hack is fairly easy to do as long as you can find away to open the cover on your donor camera.

Once completed, the resulting relay controller will allow any external electronic device to focus and then take a photo, essentially duplicating the operation of the two position shutter release trigger on your camera. Also, note that your camera will not be usable for regular photography after this hack as the original shutter release switch will be removed.

Figure 1 - This camera will be converted for external shutter control
Figure 1 – This camera will be converted for external shutter control

The sacrificial camera shown in Figure 1 is an HP Photosmart M547 digital camera with an 8 megapixel imaging system. This camera has been around the world and dropped in an ocean, but despite some dents and scratches it still functions perfectly, so it will begin a new life as a covert spy gadget. To open one of these small digital cameras, you will need a set of tiny screwdrivers, a small knife and a whole lot of patience. Since the goal of manufacturing is to keep costs to a minimum, the cases on these cameras are often snapped together, which will require some careful prying to open them up.
Figure 0 - A long range infrared illuminator can be made using many LEDs
A long range infrared illuminator can be made using many LEDs

There are times when the small infrared LED ring built into a security camera will not cover the range or field of view you require, so you will need to find another invisible light source. Some large infrared illuminators use powerful incandescent light sources that are passed through an infrared pass filter, causing only the infrared component of the light to come through the filter. These types of infrared illuminators create intense heat due to the fact that the white light source must be fully enclosed and burn the unwanted light energy off as radiated heat. Because of this intense heat, incandescent filtered illuminators cannot be used indoors and may not be suitable for many outdoor installations.

The good news is that LEDs can be used to create a very powerful infrared illumination system if you use enough of them. Ok, you need a lot of them, but these days they can be purchased for only pennies a piece if ordered in quantities of hundreds or more. The bad news is that you will need to do a lot of soldering, even on a small array of 16 by 16 LEDs, which will have more than 512 connection points.

Of course, many circuit board houses offer proto service and you could have a very large LED array circuit board made for under $100 if you shop around. If you are patient and like to solder, then any size array can be made on some perforated circuit board, resulting in a very high power illumination system that will only cost you 1/10th of what a manufactured unit would cost.

 

Figure 1 - LEDs purchased in large quantities can often be found at bargain prices
Figure 1 – LEDs purchased in large quantities can often be found at bargain prices

Before you decide on making a huge array that will light up an entire city block, do a little research on bulk LED prices and power requirements because an array will become hungry on both counts. I built two version of the LED array – one using a hand wired perforated board having 13×19 LEDs and a much larger PCB version having 32×48 LEDs. So the smaller LED array has 247 LEDs and the larger array has a whopping 1526 LEDs! Make no mistake – it takes a good chunk of power to crank up 1526 LEDs to their maximum potential, and even at 10 cents per LED, that adds up to $154 just for the LEDs.

Start by calculating how much infrared radiation you will need in order to light your scene. Limitations will likely be the focal range of your camera since details are lost on most security cameras after about 50 feet. This distance is also about as far as an LED can reach, no matter how many you add to the array, so the equation then becomes how wide and how bright do you need the scene? A 20 foot by 20 foot interior room will shine like mid-day with an array of 16×16 LEDs at each corner of the room, but the massive array I built is almost too bright to be used indoors.

If your camera will stay in a fixed position, then a single array is best, but for general room illumination, it is better to divide up your LEDs into two or more arrays for even lighting. Think of a 16×16 LED array to be about the same as a typical hand held flashlight for both output power and field of view. My 32×48 array acts more like a 500 watt halogen light source when placed in a small room.

There are several varieties of infrared LEDs, ranging in size, field of view, output power, and effective light color. The most commonly used infrared LEDs output 940 nanometer infrared light which is far beyond the human visual range, and fairly detectable by any non filtered video camera. There are also infrared LEDs available for the 800 to 900 nanometer range. These are even better for use in night vision applications, but there will be slightly detectable red glow as the human eye can faintly detect this band of light.

If you have seen an outdoor night vision security camera after dark, then you are probably familiar with this dull red glow. The LEDs shown in Figure 1 are commonly available 940 nanometer types purchased in bulk from an Internet based supplier.

Experiments using high power infrared laser diodes and modules for night vision illumination.
Figure 0 - Build a long range laser night vision illuminator
Build a long range laser night vision illuminator
Infrared LEDs are the most widely used source of infrared radiation for night vision illuminators because they are inexpensive, easy to connect, and possess no safety hazards because they are human eye safe and do not radiate much heat.

The drawback to LED based night vision illumination systems is that they are not really useable at distances of more than 100 feet no matter how many LEDs you use in the array. Filter based night vision illuminators that change visible light into infrared light are capable for much greater distances, but they suffer from huge energy losses due to massive heating of the filter material and because of this, require massive amounts of current and are only suitable for outdoor use. A laser on the other hand, is capable of extremely long distance illumination and is probably the most energy efficient source of bright light possible.

The main problem with using infrared lasers to create night vision illuminations systems is that there are safety issues that must be addressed, especially when using lasers with a rating higher than Class IIIa, or lasers that have an output power of more than 5mW (milliwatts). Class IIIb and Class IV lasers can output as much as 500 mW, and they are certainly not eye safe, especially when highly focused. A laser that outputs only 50 mW may seem like nothing, but be aware that instant eye damage could occur if you hit your retina with a focused beam. Using infrared lasers makes this situation so much more dangerous because you cannot see the beam, and your blink reflex will not help save your vision in the event of an accidental exposure to the laser beam.

Do not continue with any of these experiments unless you are well aware of the dangers involved and have proper laser safety equipment and experience in using higher powered lasers. You can still create a useable short range laser illuminator using a lower power 5mW infrared laser diode or module, so consider starting with a Class IIIa laser if you want to experiment with laser night vision illumination.

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Convert any camcorder for use as a stealthy portable night vision system
Figure 0 - This camcorder uses a spy camera to see invisible infrared light
This camcorder uses a spy camera to see invisible infrared light

Camcorders a generally designed for well lit scenes, using the light to create a quality color image for recording. To ensure that the image is seen by the camera in a similar way to our eyes, only the portion of the light spectrum that is visible to our eyes is processed. Infrared light falls just below red on the light spectrum, making up the wavelengths from about 750 nanometers to about 1500 nanometers. This light cannot be seen by human eyes, but it can easily be seen by the CCD imaging system in the camera, allowing it to be used as a night vision viewer.

Unfortunately, you cannot simply add an infrared illuminator to your camcorder and use it to capture night vision video because the CCD imager contains a glass filter that blocks out most of the infrared light. The good news is that most camcorders allow a secondary video input to be recorded, and by feeding the output from a small black and white spy camera into this input, you can give your camcorder the ability to record night vision scenes that have been lit by some type of infrared illuminator.

This project uses an inexpensive camcorder and a $20 black and white spy cam along with one of the LED illuminators shown earlier to create a portable stealthy night vision camcorder.

Figure 1 - Any camcorder with an external video input will work for this project
Figure 1 – Any camcorder with an external video input will work for this project

Most video camcorders allow an external video source to be plugged in, essentially replacing the built in CCD imager with some other compatible video source. This video input will often have some custom manufactured input jack with a label of “external”, “line input”, or “AV input”. You will need the cable that came with the camcorder in order to make this project as each manufacturer will have its own special cable for that model of camera.¬†On the older tape based camcorders like the one shown in Figure 1, there was a 1/8 jack “standard”, that used a 4 ring 1/8 inch male plug like the one shown in Figure 1, allowing any composite video source to be fed into the camera.

You will have to identify both the external video input and acquire the proper input cable in order to build this project, but if you kept all of the accessories from your camcorder, then that odd cable will probably be still sitting in the box, as it usually not used. Some manufacturers like to chisel the customer out of more money by making their own special connectors and then charging a ridiculous amount for the cable, so check your camcorder manual to make sure your camera supports video input and that you can acquire the necessary cables for a fair price.

Create a handheld infrared illumination system using a flashlight and common materials

Figure 0 - This project will explore several ways to convert visible light into infrared light
This project will explore several ways to convert visible light into infrared light

Although infrared LEDs are the most common source of invisible light for a night vision device, they are certainly not the only option available, nor are they always the best. Depending on your camera type and setup, you may need a hand held source of infrared light that can be rapidly moved around the scene, or possibly an infrared light source that differs in wavelength from the standard 800 nanometer to 950 nanometer wavelength of the standard infrared LEDs.

Infrared light falls just below red on the light spectrum, making up the wavelengths from about 750 nanometers to about 1500 nanometers. This light cannot be seen by human eyes, but it can easily be seen by most video cameras, making it useful as a covert lighting method in night vision systems. Some video cameras can even see part of the ultraviolet light spectrum from 200 nanometers to 400 nanometers. That will be covered here as well.

The goal will be to pass white light through various materials that will attempt to block out all of the visible light and only pass the light that is invisible to the human eyes, yet visible to most security cameras and spy cameras.

Figure 1 - Infrared pass filters can be made from many different materials
Figure 1 – Infrared pass filters can be made from many different materials

A filter that blocks out all light except for the small portion of the spectrum that falls between 800 nanometers and 1000 nanometers is called an infrared pass filter. This effect is exactly the same effect seen by placing a colored lens over your eyes to see the world in a different color tone. If you place a green piece of translucent plastic over your eyes, the world will look green because only the light from the 490 nanometer to 560 nanometer wavelength will reach your eyes.

An infrared filter will do the exact thing, but since you cannot see infrared light, the filter material will seem completely dark to your eyes. When you place an object made of translucent infrared material in front of a video camera, it will look completely clear, as if the camera has some special ability to see through a solid object.

This infrared pass filter effect can be exploited to create a very powerful infrared illuminator by passing white light through the filter to extract and send out only the infrared light that the video camera can see. The benefit to this approach over using infrared LEDs is that a very small and powerful illuminator can be made, as well as a very large and extremely bright illuminator.

The objects shown in Figure 1 all exhibit some infrared passing abilities, which will be explored using a small black and white security camera and some white light from an incandescent flashlight bulb.

 

LED Array Illuminator

A long range infrared illuminator can be made using many LEDs
There are times when the small infrared LED ring built into a security camera will not cover the range or field of view you require, so you will need to find another invisible light source. Some large infrared illuminators use powerful incandescent light sources that are passed through an infrared pass filter, causing only the infrared component of the light to come through the filter. These types of infrared illuminators create intense heat due to the fact that the white light source must be fully enclosed and burn the unwanted light energy off as radiated heat. Because of this intense heat, incandescent filtered illuminators cannot be used indoors and may not be suitable for many outdoor installations.

The good news is that LEDs can be used to create a very powerful infrared illumination system if you use enough of them. Ok, you need a lot of them, but these days they can be purchased for only pennies a piece if ordered in quantities of hundreds or more. The bad news is that you will need to do a lot of soldering, even on a small array of 16 by 16 LEDs, which will have more than 512 connection points. Of course, many circuit board houses offer proto service and you could have a very large LED array circuit board made for under $100 if you shop around. If you are patient and like to solder, then any size array can be made on some perforated circuit board, resulting in a very high power illumination system that will only cost you 1/10th of what a manufactured unit would cost.

Figure 1 - LEDs purchased in large quantities can often be found at bargain prices
Figure 1 – LEDs purchased in large quantities can often be found at bargain prices

Before you decide on making a huge array that will light up an entire city block, do a little research on bulk LED prices and power requirements because an array will become hungry on both counts. I built two version of the LED array – one using a hand wired perforated board having 13×19 LEDs and a much larger PCB version having 32×48 LEDs. So the smaller LED array has 247 LEDs and the larger array has a whopping 1526 LEDs! Make no mistake – it takes a good chunk of power to crank up 1526 LEDs to their maximum potential, and even at 10 cents per LED, that adds up to $154 just for the LEDs.

Start by calculating how much infrared radiation you will need in order to light your scene. Limitations will likely be the focal range of your camera since details are lost on most security cameras after about 50 feet. This distance is also about as far as an LED can reach, no matter how many you add to the array, so the equation then becomes how wide and how bright do you need the scene? A 20 foot by 20 foot interior room will shine like mid-day with an array of 16×16 LEDs at each corner of the room, but the massive array I built is almost too bright to be used indoors. If your camera will stay in a fixed position, then a single array is best, but for general room illumination, it is better to divide up your LEDs into two or more arrays for even lighting. Think of a 16×16 LED array to be about the same as a typical hand held flashlight for both output power and field of view. My 32×48 array acts more like a 500 watt halogen light source when placed in a small room.

There are several varieties of infrared LEDs, ranging in size, field of view, output power, and effective light color. The most commonly used infrared LEDs output 940 nanometer infrared light which is far beyond the human visual range, and fairly detectable by any non filtered video camera. There are also infrared LEDs available for the 800 to 900 nanometer range. These are even better for use in night vision applications, but there will be slightly detectable red glow as the human eye can faintly detect this band of light. If you have seen an outdoor night vision security camera after dark, then you are probably familiar with this dull red glow. The LEDs shown in Figure 1 are commonly available 940 nanometer types purchased in bulk from an Internet based supplier.