To Jim Weir

Stealth Pilot writes:

charlie, assuming that you are using a 12 volt bus, all you need to do
to use an LED is put a 680ohm resistor in series with it.

Huh? You can't generalize about LEDs like that! There are many different
LEDs with different electrical characteristics. Given the OP's post,
you can't even state that a simple resistor is what he wants; he may
want variable lighting, in which case a potentiometer is what's needed.

If the OP doesn't get a reply from Weir, I suggest the Matronics
AeroElectric list at http://forums.matronics.com/viewforum.php?f=3

--
Too bad you can't just grab a tree by the very tip-top and bend
it clear over the ground and then let her fly, because I bet
you'd be amazed at all the stuff that comes flying out.
- Jack Handey

On Fri, 08 Jan 2010 16:54:14 -0800, Bug Dout
wrote:

Stealth Pilot writes:

charlie, assuming that you are using a 12 volt bus, all you need to do
to use an LED is put a 680ohm resistor in series with it.

Huh? You can't generalize about LEDs like that! There are many different
LEDs with different electrical characteristics. Given the OP's post,
you can't even state that a simple resistor is what he wants; he may
want variable lighting, in which case a potentiometer is what's needed.


I can state what I like. it is a free society.
what I wrote works for me.
ymmv
Stealth Pilot

"Stealth Pilot" wrote in message
...

I can state what I like. it is a free society.

Yes you can. Even if it happens to be wrong.

Vaughn

Stealth Pilot wrote:
On Fri, 08 Jan 2010 16:54:14 -0800, Bug Dout
wrote:

Stealth Pilot writes:

charlie, assuming that you are using a 12 volt bus, all you need to do
to use an LED is put a 680ohm resistor in series with it.

Huh? You can't generalize about LEDs like that! There are many different
LEDs with different electrical characteristics. Given the OP's post,
you can't even state that a simple resistor is what he wants; he may
want variable lighting, in which case a potentiometer is what's needed.


I can state what I like. it is a free society.
what I wrote works for me.
ymmv
Stealth Pilot


Quite so. Moreover, the idea of providing an individual series resistor
to pass about 20 mA works for a good variety of LEDs.
Focussing on the desire to dim a LED, there is no reason (that I know)
not to reduce the current. This has the great advantage over pulse width
modulation that it does not kick up radio interference. There are LED
drive chips on offer now that might suit....

Brian W

brian whatcott wrote:


Quite so. Moreover, the idea of providing an individual series resistor
to pass about 20 mA works for a good variety of LEDs.
Focussing on the desire to dim a LED, there is no reason (that I know)
not to reduce the current. This has the great advantage over pulse width
modulation that it does not kick up radio interference. There are LED
drive chips on offer now that might suit....

Brian W

Maybe this will help the builder. A current source (rather than a
voltage source) will make the LED brightness varaiable. A typical (red)
LED runs at about 20 mA for full brightness, while dropping about 1.7V
across the LED. Lowering this current dims the LED. The shown circuit
can be set to supply up to about 400 mA, enough for about 20 LEDs. Of
course, he will want to use red LEDs in place of the white ones drawn in
the circuit...

http://radiolocation.tripod.com/LEDd...ampDimmer.html

Scott

Scott wrote:
brian whatcott wrote:


Quite so. Moreover, the idea of providing an individual series
resistor to pass about 20 mA works for a good variety of LEDs.
Focussing on the desire to dim a LED, there is no reason (that I
know) not to reduce the current. This has the great advantage over
pulse width modulation that it does not kick up radio interference.
There are LED drive chips on offer now that might suit....

Brian W

Maybe this will help the builder. A current source (rather than a
voltage source) will make the LED brightness varaiable. A typical (red)
LED runs at about 20 mA for full brightness, while dropping about 1.7V
across the LED. Lowering this current dims the LED. The shown circuit
can be set to supply up to about 400 mA, enough for about 20 LEDs. Of
course, he will want to use red LEDs in place of the white ones drawn in
the circuit...

http://radiolocation.tripod.com/LEDd...ampDimmer.html

Scott


Didn't Weir do an article in "Kit Planes" awhile back on this subject?

Dan, U.S. Air Force, retired

Scott wrote:


Maybe this will help the builder. A current source (rather than a
voltage source) will make the LED brightness varaiable. A typical
(red) LED runs at about 20 mA for full brightness, while dropping
about 1.7V across the LED. Lowering this current dims the LED. The
shown circuit can be set to supply up to about 400 mA, enough for
about 20 LEDs. Of course, he will want to use red LEDs in place of
the white ones drawn in the circuit...

http://radiolocation.tripod.com/LEDd...ampDimmer.html

Scott


Didn't Weir do an article in "Kit Planes" awhile back on this subject?

Dan, U.S. Air Force, retired

Dunno. Haven't gotten the rag in a couple years. Price stayed the same
but page count went down, didn't find it cost effective, with all the
magazines I was gettin'. That said, I wouldn't doubt it was covered at
one time or another...

Scott wrote:
brian whatcott wrote:


Quite so. Moreover, the idea of providing an individual series
resistor to pass about 20 mA works for a good variety of LEDs.
Focussing on the desire to dim a LED, there is no reason (that I
know) not to reduce the current. This has the great advantage over
pulse width modulation that it does not kick up radio interference.
There are LED drive chips on offer now that might suit....

Brian W

Maybe this will help the builder. A current source (rather than a
voltage source) will make the LED brightness varaiable. A typical (red)
LED runs at about 20 mA for full brightness, while dropping about 1.7V
across the LED. Lowering this current dims the LED. The shown circuit
can be set to supply up to about 400 mA, enough for about 20 LEDs. Of
course, he will want to use red LEDs in place of the white ones drawn in
the circuit...

http://radiolocation.tripod.com/LEDd...ampDimmer.html

Scott


Yep.

Here's another idea that sticks with the non pulsed approach.

It uses a variable voltage reg in constant current form - allowing a
string of several LEDS as is:
http://www.instructables.com/id/Circuits-for-using-High-Power-LED_s/step11/an-even-simpler-current-source/

...or in TinyURL format:
http://tinyurl.com/yb9kyyr


....this could be massaged to provide the drive for 24 LEDs at rather low
cost and component count.

Brian W