AFAIK (my technical college time is 20 years behind me now) You need to feed a led with a current of aproximity 15 mA (should have to look a datasheets for this). Depending on the color of the led the tension could be in the neighbourhood of 1.2 V
So the value of R would be R = (UHD - 1.2)/15 mA This are a few standard rules out of the head better values: http://www.kpsec.freeuk.com/components/led.htm You have to be aware of the following: UHD is the tension measured without charge (without led). The value of R can be a variable of the resistance of the power supply and the resistor you switch in serie For this reason R = R0 + R1 This diagram would be closer to the real world output ^^ HD LED |---|>|----+ HD+ o--[ R0 ]--o---[R1]---+ c |-----+ UHD0 UHD |---|(-----+ | HD- o----------o---------------------------+ R0: circuit uncharged: no led. UHD0: Voltage uncharged. 1) measure UHD0: uncharged 2) measure R0 For this we need one suplementary step: R' = UHD0/15mA We connect R' instead of the led and measure the voltage drop UHD' So R0 = (UHD0 -UHD')/15mA Now we have UHD0: The uncharged value of the led voltage R0: The own resistence of the power circuit Iled: The current trough the led (15mA) R = UHD0/Iled R1 = R -R0 Most circuitry has already it's own resistance R0, so it is possible you leave R1 = 0. Afterwards you need to determine the value of C As Chris Ellis pointed out: T = 2pi.rc or as most engineers use to calculate 6,25RC So the value of C must be much greater the the time in seconds it flickers C >> T/(6.25R) > Karl Lattimer wrote: > >>After sitting, almost transfixed on my mac's sleep light as it slowly >> rises >>and falls a little college electronics returned to me. >> >> ^^ HD LED >> |---|>|----+ >>HD+ o--[ R ]--+ c |-----+ >> |---|(-----+ | >>HD- o--------------------------+ >> >> >>Now I'm pretty sure this is right, off the top of my head, and would >> relieve >>the headache a hard disk light in a freevo can cause. >> >>The only problem is I can't rightly remember the method of determining >> the >>values of R and c (my notes are long gone), I'll keep looking, and update >> as >>necessary and of course post a wiki. The thing is, what would be a good >>timing? Should we try and time it so our breathing comes in time with it >> as >>we watch a movie? >> >>Regards >>Karl, >> >> >> >> >>------------------------------------------------------- >>SF email is sponsored by - The IT Product Guide >>Read honest & candid reviews on hundreds of IT Products from real users. >>Discover which products truly live up to the hype. Start reading now. >>http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click >>_______________________________________________ >>Freevo-users mailing list >>Freevo-users@lists.sourceforge.net >>https://lists.sourceforge.net/lists/listinfo/freevo-users >> >> > sorry for the second reply, I also should introduce myself a bit, i'am > currenlt studding for a-levels and will be going to uni to studdy > electronic engineering so are quite ok at electronics. I have put the > circuit through so circuit modellign software I have and it did not seem > to work. (this is not a 1005 accurate but i will also construct to have > a look, it is an excellent IDEA. I think what we may need is a RC > filter. > > > ------------------------------------------------------- > SF email is sponsored by - The IT Product Guide > Read honest & candid reviews on hundreds of IT Products from real users. > Discover which products truly live up to the hype. Start reading now. > http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click > _______________________________________________ > Freevo-users mailing list > Freevo-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freevo-users > > > -- > This message has been scanned for viruses and > dangerous content by OpenProtect(http://www.openprotect.com), and is > believed to be clean. > > -- This message has been scanned for viruses and dangerous content by OpenProtect(http://www.openprotect.com), and is believed to be clean. ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ Freevo-users mailing list Freevo-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freevo-users
