Introduction: Yet Another Simple Nightvision

Have you ever wonder of making your own nightvision device? Check this out!

Step 1: What Is Light?

„Light” or „visible light” is a part of an electromagnetic radiation spectrum, with wavelength noticeable by human eye. Eye can see waves from around 380nm to ~750nm. Nightvision operates in range of wavelengths right above visible light, 800-1000nm. This range is called infrared, IR. But sometimes light happens to act as a wave, and sometime it acts like a particle. This particle is called „photon”. Photons are packets of energy emitted by some source, i.e. LED. For clearance and simplification, lets say that light is stream of photons (0-mass particles or "portions of energy") that moves along the sinus-like path (wave).
For more info about light and EMR i recommend to check wiki pages:
http://en.wikipedia.org/wiki/Light
http://en.wikipedia.org/wiki/Electromagnetic_radiation

Light, which wavelength is higher than 750nm are called infrared. Waves with wavelenght lower than 380nm are called ultraviolet.

Step 2: How Nightvision Works?

Basically, real nv device is an light amplifier. It catches stream of photons from infrared range and amplify it in photomultiplier (makes stream more dense). Stream of photons bombs photoluminescent screen (or it is changed to the electron stream and bombs electroluminescent screen), makes it glow in visible light. Old generations had to be used with additional IR light to illuminate things around and catch reflected photons. NV systems with illuminators are called "active".
New generation of NV have so high amplification rate, that it does not need any additional source of IR light. It uses ambient IR light emitted by stars/moon/etc. Those are called "passive".

Homemade NV is based on another rule. It uses CCD's ability of registering near IR light. It have to be active device, with illuminator, because this ability is rather fallout than intentional, so it is not so big.

Step 3: Things Needed

- Analog viewfinder from an old VHS camera
- Analog board camera
- source of IR light
- rechargeable battery
- step-up and step-down converters
- discharge/low voltage level indicator

Whole those things will be connected as diagram above shows. Colors of cables matches real colors I've used.
Part surrounded by dashed line is optional. I'm going to use IR source with external power supply, so this part of schema will not be used.

Step 4: Board Camera

In final version I've used small color CCD board camera, which could be easily get from old security cam or as brand new module from retailers. Black&white camera are better for this purpose, it has better sensibility! It runs on 12VDC and is connected by small, 4-pin connector: yellow=12V, black=gnd, blue=analog signal out, black=gnd.
During tests and prototyping I've used another camera, with built-in IR diodes. Less cables on the desk means less chance for shorting circuit.

Security cams have hadn't IR filters in front of CCD matrix. Any other cam could have that. But it is really simple to take it off. Just unscrew lens and remove piece of glass with orange-blue shine.

Step 5: Viewfinder

Viewfinder was taken from some old, analog VHS camera. Usually it was powered by 5V DC, but some models could be supplied by 9V DC. If cables from viewfinder aren't described or marked by colors (usually red=5V DC; black=ground; blue (or white)=signal input) you have to determine pinout. Easiest way is to dismantle whole device and search for big areas of cooper on PCB. This will be common ground. Using the multimeter, set to resistance measurement, check which cable has lowest value between him and that cooper plane. To the cable already found, connect negative output of your 5V power supply. Then, connect positive output to other cables, one by one, until you see display glow. One of the cables that remains is video signal input. Find it using same method, connect with camera's video output, one by one.

Step 6: Battery

You can use almost all available RC LiPo, LiFePo, liIon, NiMh, NiCd batteries, packets of 18650 or normal AA batteries. But voltage have to be above minimal voltage input for converters. Good choice will be something between 7 and 12V. I have used standard mini-cell, 9,6V, NiMh RC rechargeable packet, about of 1500mAh capacitance.

Step 7: Step-down and -up Converters

In this device, I needed 2 separate levels of voltage. 12VDC for camera and 5VDC for viewfinder. First thought  was simple: 7805 and 7812 stabilizers. Bad idea. First, because of necessary dropout voltage ~1,3V, it would enforce very big battery: 14,4V battery = 12cells (13,3V is the minimum for 7812 stabilizer). And second, there will be huge amount of energy wasted because of heating 7805 ic. Heat is also undesirable for CCD camera; ability of catch photons drops with temperature increase.

My battery, which i wanted to use, was 9,6V. Because of that i could use 7805 stabilizer for 5VDC, but again, heating problem occurs. So I've decided to use LM2596 based step-down converter. It has more efficiency than stabilizers and produces less heat. Almost perfect.

To run camera properly, I've needed some voltage boost. Magic is done by pulse step-up converter. It's based on TI LM2577 ic.
Ready-to-use modules are available on ebay for few dollars.

Step 8: Low Voltage Indicator

Low voltage indicator is obligatory, because of using pulse power converters. Converters acts like a joule thieves that "sucks" whole energy from battery. But, when voltage on single cells drops under type-specified minimum value, battery is broken. This minimum voltage is 0,9V/cell for NiCd, 1V/cell for NiMh and about 3V for all types lithium cells. Indicator's LED stay off whole time voltage is above minimum level and turns on, when voltage drops under limit set by potentiometer.
Circuit is very simple. It contains 3V6 Zener diode, two multi-purpose transistors, LED, two resistors and potentiometer. Designed in Eagle PCB to easily fit on prototype board.
Setting voltage limit is very simple with adjustable power source. For my case, I wanted to set 8,0V as trigger for indicator. 8V because 8 NiMh cells * 1V/cell = 8V. Set 8V on adjustable power source. Then turn indicator's potentiometer till light gets off. Once you get it, turn slowly opposite way till you get LED lights again. Done.

Step 9: IR Light

Ir light is not an final version. It is made using 10 low power 850nm LED diodes, overdriven by PWM circuit. Maximal current limit is set to twice that led could hold during normal, continuous operation. Why diodes had not burn? Because fill of PWM signal is about 10-20%, with 10hKz cycle, as far as I remember. This causes LEDs "flashes": 10-20% of time diodes are on and the rest time of every cycle it remains off . And could spread thermal energy from junction to environment.
I know that this circuit probably is not perfect. It was the first one I've ever designed on my own. Couple years ago.
I would like to replace IR source to 1-3W 940nm power LED, as soon as possible.

Step 10: Tests, Part 1, Day

Time to put it together.
Using block diagram from step 3, I've connected all the devices. Instead of battery, LM317 power supply was used (only for tests, set to nominal battery voltage = 9,6V). Converters are separated by card with some of my notes/ideas, just in case.

Image appears on viewfinder's screen. It means that whole circuit works well. If there will be some artifacts on the screen, try to put electrolytic capacitor between viewfinder power lines. Watch for polarity, capacitors negative electrode have to be connected to negative voltage terminal and positive electrode to positive terminal!  I've used 330uF/16V, but 1000uF/16V probably would be even better.

Step 11: Tests, Part 2, Night

Previous step tests was successful, so time to check if it is really able to see in night. Now, with battery instead of LM317.
First image shows one of my shelves. Check it in daylight, and see how it looks being seen in nightvision!
Photos are small, because it is very hard to make it good with simple digital cam in night (without flash).

Step 12: Enclosure

Last thing to do is to put whole parts into some case. 40 x 60mm conduit would be good in this role. I've made holes to screw viewfinder and picatinny rail (this will be base for IR source mount). Also, holes for discharge indicator and turning switch will be needed.
I've cut the cables for proper length. It should be long enough to easily fit it into place. Both power converters was insulated by heat shrink tube. Whole circuit was connected by electrical screw terminals.
What else to say? It is done.

Thanks for reading. If You like this instructable, don't forget to check the rest of my tutorials.
Also, you can see Polish version here: http://majsterkowo.pl/prosty-noktowizor/

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