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I’ve designed the circuit around 5V, as this is what you get from the computers USB port. You can usually get about 500mA from it so if your webcam needs 300mA (like the PCVC740k) then you have 200mA to play with. Each LED needs about 20mA 1.8V and 50mA 2.4V to get started, so if you have 5V then you can use 2 LED’s (2*2.4=4.8) in serial with an resistor of 68Ω (5-(2*1.8)*50=70) (the 50 is something I got from my local component supplier). In this case with 12 LED’s the circuit will use 100mA which is enough to run it on the existing USB port with the camera.
A note on assembling this, mount the LED’s with the short leg towards ground. I’ve used 2 circuits like this so that I can put one on each side of the camera. (something that I didn’t do in the end) While building a circuit it’s good practice to test the LED’s when each section is ready. You do this by turning on the power and looking at them through the cam, you should then see the light emitting from the LED’s. The reason for testing it is that when I build my first setup, I found one dead LED while building it and one later on. |
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Next, let’s have a look how to take apart and modify that webcam and it’s IR filter.
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Here’s a photo taken when the LED’s are on, without a flash. Note the two top left LED’s not burning. That’s because of one of them not working. Another thing to note is that the light from the LED’s are not visible to the eye, they just look turned off.
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January 11th, 2006 at 21:43
You are certainly not an electronics engineer.
(5-(2*1.8)*50=70)??
Last time I checked this wasn’t true.
5-180 = -175.
Oh now I see what you meant. You meant: ((5-(2*1.8))*50=70
In that case, the reason you multiplied by 50 was because (due to reciprocals) multiplying by 50 is the same as dividing by 0.02 A (or 20 mA). Thus, using Ohm’s law of V=IR or in this case R=V/I where V=1.4 (5 minus the two 1.8V LED voltage drops in series), I=50 Therefore, an appropiate resistor would be a 70 Ohm Resistor.
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January 26th, 2007 at 17:19
Here’s a video showing the conversion process of a standard webcam into an infrared cam:
http://images.metacafe.com/thumb/385098/2760327/4/submitter_catalog/0/transform_your_webcam_into_an_infrared_cam.jpg
(nice examples of use at the end!)
January 21st, 2008 at 12:27
Very useful article. Thanks