> Easy build setup with SFH485P, Anyone can build this ! (for 5v Usb serial build see Page 2)
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nex |
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Class : Apprenti
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Registered on : 26/06/2012
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I have a question. I ordered most of my things from Farnell, all is good except ... the resistors are for 250mA (I have both 6.8 and 10 Ohm) and I will be supplying 500mA to the circuit. Usually im not that bad at electronics but Im not sure if this will be a problem.
Which current do I need to look at when picking the resistor? The amount supplied or the actual current that will pass through the circuit after the resistor? I saw that 250mA resistors are suggested as a suitable choice so I went for them  |
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Steph |
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Registered on : 16/11/2007
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Hi,
I think there is confusion between current and power. You do not apply 500mA current. Instead the LEDs let current flow, that you limit by adding the resistor. So in function of current and voltage the rate of energy P is:
W = A x V or A² x Ohm
Resistor are classed by max. Watt. In your case 1/4W (250mW).
So for example using three SFH485 with 6.8Ohm and 5V Powersource gives you:
I = V / R = (5V - 1.5Vled x 3) / 6.8Ohm = 0.073A
The circuit let 73mA flow.
P = R x I² = 6.8 x 0.073² = 0.036W
36mW - No problem for your resistor.  |
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nex |
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Class : Apprenti
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Registered on : 26/06/2012
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Steph @ 26/06/2012 - 13h22 a dit: Hi,
I think there is confusion between current and power. You do not apply 500mA current. Instead the LEDs let current flow, that you limit by adding the resistor. So in function of current and voltage the rate of energy P is:
W = A x V or A² x Ohm
Resistor are classed by max. Watt. In your case 1/4W (250mW).
So for example using three SFH485 with 6.8Ohm and 5V Powersource gives you:
I = V / R = (5V - 1.5Vled x 3) / 6.8Ohm = 0.073A
The circuit let 73mA flow.
P = R x I² = 6.8 x 0.073² = 0.036W
36mW - No problem for your resistor.
Thanks, I wasnt really sure if its like that, I should've studied electronics harder when I had the chance. Just got everything I need except the frame for the LED's, currently looking through the picture gallery for ideas.
Thanks for the extremely fast answer!
Regards
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TwoToes |
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Class : Apprenti
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Registered on : 01/07/2012
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hello!
another noob here.
i just wanted to double check before ordering...
LED's,
Resistor: 6.8ohm, 10ohm
fuse
are these the right parts for a usb serial build?
hope so, cause if not, the last 12 pages of this thread made no sense to me... 
edit: for prosperities sake and uk peoples
Edited by TwoToes on 04/07/2012 at 16h26. |
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Steph |
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Class : Moderator
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LEDs - ok
Resistor - ok (perhaps take 6.8Ohm too, if you need brighter LEDs.)
Fuse - ok, but you do not need fuse, if you power your mount with a USB-power adapter, what I highly recommend. Fuse is no full guarantee for
your motherboard.
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TwoToes |
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cheers dude.
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TwoToes |
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i don't have a usb power adapter (weird, i know) but what i do have an old two pin phone charger...
input: 100-240v ~ 50-60Hz, 150mA
output: 4.9v, 700mA
...?
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Steph |
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That will be all right too.
You only have to figure out, if it's a switched-mode or linear power supply.
Switched mode power supply: Voltage varies little with load. Model is lighter, because transformer is smaller.
Linear power supply: Voltage varies with load, so you have to take into account that these unregulated power supplies usually provides a higher voltage than indicated (about 15-30%). These models are mostly bigger and heavier for the same output than switched- mode power supply's.
If he's not older than five years, it will probably be a switched-mode.
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tzen |
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Class : Apprenti
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Registered on : 21/08/2012
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nm
Edited by tzen on 21/08/2012 at 16h54. |
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doveman |
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I've built just a single LED model at the moment and got that working OK from about 2-2.5ft away with my PS3 Eye.
What I'm trying to do now is use it with the PS3 Eye on my TV and me on the sofa, which is about 6ft. I can just about get it working after a lot of tweaking off the PS3 Eye's gain and exposure and Freetrack's threshold settings but I only get a cross, not a proper red dot and it can't properly lock on so the green light keeps turning red.
I'm using a USB power adapter and first tried with a 10 ohm resistor (I'd already built with that for my desk setup) and when that didn't work with a 6.8 ohm but even with the curtains shut to keep out the daylight it's not working well enough.
So is there anything else I can do to get a nice solid red dot?
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Steph |
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Try with three LEDs in a bundle.
What kind of filter do you use?
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doveman |
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Steph @ 03/09/2012 - 07h07 a dit: Try with three LEDs in a bundle.
What kind of filter do you use?
OK, I'll try.
I wasn't using any filter when it was on the TV but then I put it back on my monitor, so it was 2-3ft away and put a bit of floppy disc material over the lens and I had a lot of trouble even with that. I think I had better results without the filter with the 10ohm model but I'll have to compare the two properly.
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Steph |
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Floppy disk is a very bad filter material, because it blocks all light, even a big part of Ir-band. Try other solutions: Layers of coloured plastic film or even simply: Take a piece of transparent plastic film, (from packaging or overhead sheets, it doesn't need to be in perfect optical quality, but without distortion). Paint both sides crosswise with a black felt-tip pen, (I used a windows marker for best uniformly coating.) This is a perfect ir-pass-filter giving the same results as my electronic photo diode filter.
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doveman |
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Ah, OK thanks. I only used it as I saw other people suggest it. Is undeveloped camera film equally useless?
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Steph |
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Yes, developed, unexposed film is much better than floppy disk.
Look at this table, it's quiet illustrative: http://forum.free-track.net/index.php?showtopic=3205 |