Date: Sun, 3 Apr 2011 07:00:14 -0700
Reply-To: Al Knoll <anasasi@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Al Knoll <anasasi@GMAIL.COM>
Subject: Re: replacing lightbulb for heater control levers AAAK!
In-Reply-To: <BANLkTikahCESESejrkpSpLOkWUjgSpMOmQ@mail.gmail.com>
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LED stuff, yep I'm biased.
From my days as a young starryeyed stumbling fool:
"The sum of the voltages around a circuit must equal zero"
Eb=the battery voltage
Vr= the voltage drop across the resistor
Vd= the voltage drop across the LED
For the sum to be zero there must be some negative values. All the Vs we
will consider as having negative values.
The specified LED has two characteristics of interest
If = the current allowed for some particular luminance (just pick one from
the spec sheet)
Vf = the forward voltage drop across the LED at that current (likely to be
the same for the entire operating range of the particular LED)
Summing the voltages around the circuit :
Eb-Vd-Vr=0
or Eb = Vd + Vr
Knowing the If as mentioned above we know from Homies Law and some other
stuff like the current in the loop is the same through all elements:
so the current through the resistor (our quarry) is If
Vr = If*R
Since we know Vd (from the spec) and we can assume Eb is 13VDC (CEFGW)
Solving for Vr : Vr = Eb - Vd
R then becomes Vr/If =R
At least it worked that way before cellphones.
Thevenin and Norton were close friends. Russell H. Seacat was a harsh
master.
Now the question for the day regards Newtons Laws and the recent discovery
of Heisenbergs and Knolls corrolary is can you describe the three laws of
motion attributed to Newton?
Pensioner
On Sun, Apr 3, 2011 at 5:06 AM, Larry Alofs <lalofs@gmail.com> wrote:
> I remember that I used a white LED and a resistor. Unfortunately I
> don't remember any other details. :-(
>
> Larry A.
>
>
> On Sat, Apr 2, 2011 at 12:34 PM, Bill MacLachlan <billmacla@gmail.com>
> wrote:
> > OK so I found some grain-of-rice bulbs while I was cleaning things out
> > yesterday, and thought I'd get the light behind the heater control levers
> > going again. I have power to the bulb socket. I have ground from the bulb
> > socket. I have a good bulb ( touch the wires to the bulb and it lights
> > up!!!). Damned If I can figure out how to put the bulb in the socket so
> that
> > it makes contact with the ground and power supply.
> > Any suggestions? I've already had the contact wires on two bulbs fall off
> > fiddling ( carefully ) to make contact.
> >
> > Thanks All
> >
> > Bill M
> >
>
