Homage to apple, such a simple circuit, such simple idea's such ground breaking effects
K,
Chris Ellis wrote:
Geert Decorte wrote:
AFAIK (my technical college time is 20 years behind me now) You need toI must point out that T = RC not 2pi RC 2pi is used in the capacitor reactance formular but not in the timne perioc for a RC circuits
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,
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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.
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Chris Ellis
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