> which resistor do i need?
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RecTec |
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Class : Apprenti
Posts : 13
Registered on : 29/12/2009
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hello guys
first of all i want to say, that i´m really impressed by this freetrack-stuff.
it seems to work great, thanks to the people who made it possible!
im planning to build my own clip-device, but i do not exactly know which resistor i need. i took the video from viper 3 to get the basics.
http://www.youtube.com/watch?v=5QqAqb_SZV0&feature=related
here my setup:
webcam vx 3000
3 SFH485P LEDs
6 V 300ma power supply
the guy in the video uses a 15 Ohm resistor, but i do not know if that is correct for me. i´ve already tried your calculator, but i´m not good at physics, so i do not understand that stuff.
i´m using a video projector for playing, maybe the leds must be quite bright.
can anyone tell me which kind of resistor i need to get it working correct?
Edited by RecTec on 29/12/2009 at 02h14. |
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Falcon |
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Class : Apprenti
Posts : 23
Registered on : 14/11/2009
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Hi, it depends on how bright LEDs you want. Not long ago I made 6V freetrack device (using 4x 1.5V cells) and I used 51 Ohm resistor to get rougly 30mA current trough LEDs. Works well with IR filter removed from camera and using piece of floppy instead. You can see the scematics, design and final device here.
On first picture u can see other posible resistor setups and according currents. In the end I used just the 51 Ohm, being bright enough for me. |
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RecTec |
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Class : Apprenti
Posts : 13
Registered on : 29/12/2009
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thanks for the answer, already seen your garden-clip. nice work, very good idea. well done.
i wonder how this viper-guy came to a 15 ohm solution, and yours works out with 51. it seems there is a difference between using batteries and an ac adaptor, because u can choose between those two and usb power in the calculator.
i just dont want to burn too many leds by experimenting. 
any more opinions on that? |
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Falcon |
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Class : Apprenti
Posts : 23
Registered on : 14/11/2009
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Its easy, USB conector uses 5V while 4 1.5V cells makes 6V. Substract 3x1.5V for LEDs - its voltage neded to make current flow trough LEDs.
In 5V USB setup u get 0.5V after subtraction. With 15 Ohm resistors, using Ohms law, u het I=U/R=0.5/15 = 0.033A=33mA.
In 6V setups (batteries or another source) u get 1.5V after subtraction. I=1.5/50=0.030= 30mA.
BTW refereing to garden clip, don't u mean benmeijer's? |
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benmeijer |
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Class : Habitué
Posts : 208
Registered on : 19/07/2008
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RecTec @ 29/12/2009 - 20h04 a dit: ...... it seems there is a difference between using batteries and an ac adaptor, because u can choose between those two and usb power in the calculator.
any more opinions on that?
If you choose 6 v (unregulated) power supply in the "Led Assembly Wizard", it will add 30% to the voltage, so 6v --> becomes 7.8v.
read more in this Topic: http://forum.free-track.net/index.php?showtopic=1518&hl=unregulated#10053
Maybe it is better to use a 5V USB power supply, because it is regulated (5v = 5v)
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RecTec |
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Class : Apprenti
Posts : 13
Registered on : 29/12/2009
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alright, i got it now. he must have a kind of regulated power supply, that´s why it comes to 15 ohm.
i do not want to use usb, because i get trouble with my joystick sometimes, if too many usb-stuff is connected. i also already ordered this ac adaptor, would be a waste of money.
in the calculator i type in the following:
voltage 7.8 V (6+30%)
power supply unregulated (it is, i found it out)
forward voltage 1.5 V
forward current 100ma
i will order a 56Ohm 0.25W resistor now, which i guess is the right one in my case. or did i choose the wrong settings?
thanks for your help guys, really appreciate that!
this will be a great thing, if i get it to run 
Edited by RecTec on 30/12/2009 at 01h50. |
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benmeijer |
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Class : Habitué
Posts : 208
Registered on : 19/07/2008
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RecTec @ 30/12/2009 - 01h35 a dit: in the calculator i type in the following:
voltage 7.8 V (6+30%)
power supply unregulated (it is, i found it out)
forward voltage 1.5 V
forward current 100ma
i will order a 56Ohm 0.25W resistor now, which i guess is the right one in my case. or did i choose the wrong settings?
In the led wizard you should type:
Voltage: 6 V
Power Supply Unregulated
forward voltage 1.5 V
forward current 60 mA !!!!!!
as result you get 56 ohm (the wizzard adds the 30 % to the 6 V)
If you want the leds brighter (forward current greater than 60 mA) use lower values for the resistor.
60 mA .... use 56 ohm
75 mA .... use 47 ohm
100 mA .... use 33 ohm (I think this is to bright)
Order some other values for the resistor and try different values!
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jxjcksn |
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Class : Apprenti
Posts : 25
Registered on : 30/12/2009
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I have a quick question to add to the resistor.
I have ordered the SFH485P LEDs, but until they arrive I was gonna dink about with a couple I got from Radioshack.
LED Wizard ..... Putting these seetings in ....
1 Point LED
3.0v Battery Power Supply
1.28 Fv
100mA
Returns me THESE settings ....
Resistor Value - 18.5 Ohms 5%
Current - 95.6mA
Dissappated Power - .16 Watts
Total Current - 96.6mA
My question is ..... Is it the Dissappated power that dictates the wattage rating on the resistor I choose ? So in the above case I would want a resistor rated at NO LESS than a 1/4 Watt ??? (0.25)
I noticed that the Bag of resistors I picked up from Radioshack were 1/8 Watt and if I'm right they will not be enough wattage ????
Thanks guys in advance for any replies.. still trying to get my head around the math and theory.
Edited by jxjcksn on 05/01/2010 at 05h34. |
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Falcon |
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Class : Apprenti
Posts : 23
Registered on : 14/11/2009
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Easy solution: Decrease current, most people uses 25-80mA, I use 30mA which is clearly enough for IR moded webcam. As current drops, so does dissipated power. Get 70mA or less (prefreably) and you should be OK with 1/8W.
EDIT: Would go with 36Ohm(50mA@0.08 W) - 51Ohm(34mA) resistors.
Edited by Falcon on 05/01/2010 at 12h08. |
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jxjcksn |
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Class : Apprenti
Posts : 25
Registered on : 30/12/2009
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TYVM Falcon, I'm with you now and understand a little better. Radioshack in the US, Shopstock, is fairly crappy for resistors, but at least now I can play about with reduced current to reduce my wattage if I can't quite find the necessary resistor.
Made my first attempts last night, got my mobile phone camera on it to see if there was light (IR) and hey presto ! 
Now if the Wii remote would arrive I'd be a happy camper lol. |
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Chevelle |
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Class : Apprenti
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Registered on : 01/03/2011
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Hello. I recently built a 3 LED cap system and did some testing. I have also read quite a bit of information here and some of it is not the best way to go.
First, it is MUCH better to wire the LEDs in series. You will use much less power and have more uniformly lit LEDs. If you are using batteries, it is MUCH better to use 4 AAA batteries with the LEDs in series instead of 2 AA batteries with the LEDs in parallel. There is little weight difference and the AAA batteries will last a LONG time if you do things right.
The 485P LEDs have a max forward current of 100mA but if you are using a Webcam that has been modified so the IR blocking filter has been replaced with a visual blocking filter, you don't need anywhere near 100mA. It is actually too bright and can "bloom" in the image.
I have been running my 485P LEDs at 24mA on 4 AAA batteries and they are very bright over the background. (I have a 100 ohm resistor in series with the three LEDs.) Alkaline AAA batteries have a current capacity of 1200mAh. That means that at 24mA, my batteries will last 50 hours.
Hope this helps.
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