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Chief #1 19/12/2012 - 05h38

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I am trying to build my fist setup based on the serial build with a 5V phone charger from this thread: (http://forum.free-track.net/index.php?showtopic=1856). I have found the SFH485p bulbs from digikey.com (http://www.digikey.com/scripts/DKSearch/dksus.dll?Detail&itemSeq=123846259&uq=634914669067029634) but am wondering where to get the 6.8 Ohm resistors? I couldn't find any on digikey but I could be wrong. Can I get the right ones at radioshack? Thanks for any help.
Steph #2 19/12/2012 - 08h46

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Hi,


http://www.digikey.com/product-detail/en/CFM14JT6R80/S6.8QCT-ND/2617790
or
http://www.digikey.com/product-detail/en/CFR-25JB-52-6R8/6.8QBK-ND/2644
(It seems as if this one is only available by 200pce, even when min. quantity in the product table note by 1.)
Chief #3 19/12/2012 - 15h18

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Thanks for your help, I don't know why I couldn't find them there. I'm gonna buy the ones in the first link you posted along with the SFH485p leds today. The ones in the second link are $.02 more expensive, are they better than the ones in the first link? Any power supply that says 5V should be fine right? I have some old phone chargers of different current but all 5V. Thanks again
Steph #4 19/12/2012 - 16h54

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Chief @ 19/12/2012 - 15h18 a dit:

The ones in the second link are $.02 more expensive, are they better than the ones in the first link? Any power supply that says 5V should be fine right? I have some old phone chargers of different current but all 5V. Thanks again



No, there isn't a notable difference between both.

Yes, 5V phone chargers are good. As long as they can delivers more than ~250mA it's ok. Be sure that it's a switched-mode power supply not a linear power supply. (How to make the difference: http://en.wikipedia.org/wiki/Switched-mode_power_supply
Chief #5 19/12/2012 - 17h16

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I have an old blackberry charger (http://www.cellphoneshop.net/hdw17957.html) with an output of 5v and 700mA just lying around but am not sure if it is a switched mode power supply. Also I just stripped the wires and I don't see any way to distinguish which wire is the ground, how can I figure it out so that I don't wire the setup backwards?
Steph #6 20/12/2012 - 12h39

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Power supply is ok.

There are several solutions to find out which wire is positive or negative.

-Check it up with a multimeter, even the cheapest can do the job.

- Wire it up with the LED (and the resistor) for some seconds. In a dark room you will see the light red glimmer of the LED when he is right poled. Normaly it doesn't shot up your LED in one second.

- I read about this solution but never tried it out myself: (So no guaranty) ^^
You can find out the polarity with a self-made electrolysis. Dip both cable into a glass with heavily salted water and see how it forms small blisters. This accumulates to the positive pole, as the current flows from negative to positive ...

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