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#11
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To Jim Weir
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 |
#12
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To Jim Weir
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 |
#13
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To Jim Weir
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 |
#14
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To Jim Weir
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 |
#15
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To Jim Weir
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... |
#16
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To Jim Weir
Hello, Charlie ...
The main reason I post on this newsgroup is so that my answers are vetted by the group and we don't cut holes in the airplane when something obviously isn't going to work. Tell you what, and with a couple of options: 1. Post on these newsgroups in alt.binaries.scientific.electronics and attach the schematic with a request to look it over and I (as well as a dozen other folks whose opinion I value) can massage it for you. 2. Join the newsgroup Pilots Of America and post the schematic in Maintenance Bay. Again, there are folks in there who will certainly not let me give you bum information. Jim On Thu, 07 Jan 2010 15:39:13 -0500, Charlie Smith wrote: Jim, From info I have located on the internet, I have cobbled together a circuit diagram for illuminating my instrument panel using LED's. I was wondering if I emailed you a copy, would you would be kind enough to take a peek at the circuit and see if I missed anything? Electronics isn't my expertise but I enjoy it all the same. Thanks in advance, Charlie Smith |
#17
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To Jim Weir
Make that
alt.binaries.schematics.electronic Jim On Thu, 07 Jan 2010 15:39:13 -0500, Charlie Smith wrote: Jim, From info I have located on the internet, I have cobbled together a circuit diagram for illuminating my instrument panel using LED's. I was wondering if I emailed you a copy, would you would be kind enough to take a peek at the circuit and see if I missed anything? Electronics isn't my expertise but I enjoy it all the same. Thanks in advance, Charlie Smith |
#18
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To Jim Weir
RST Engineering wrote:
Hello, Charlie ... The main reason I post on this newsgroup is so that my answers are vetted by the group and we don't cut holes in the airplane when something obviously isn't going to work. Tell you what, and with a couple of options: 1. Post on these newsgroups in alt.binaries.scientific.electronics and attach the schematic with a request to look it over and I (as well as a dozen other folks whose opinion I value) can massage it for you. 2. Join the newsgroup Pilots Of America and post the schematic in Maintenance Bay. Again, there are folks in there who will certainly not let me give you bum information. Jim On Thu, 07 Jan 2010 15:39:13 -0500, Charlie Smith wrote: Jim, From info I have located on the internet, I have cobbled together a circuit diagram for illuminating my instrument panel using LED's. I was wondering if I emailed you a copy, would you would be kind enough to take a peek at the circuit and see if I missed anything? Electronics isn't my expertise but I enjoy it all the same. Thanks in advance, Charlie Smith Thanks Jim. I knew of Matronics but not these other places. This all I really need; some good, trustworthy advice. Thanks again. Charlie |
#19
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To Jim Weir
RST Engineering wrote:
Make that alt.binaries.schematics.electronic Jim On Thu, 07 Jan 2010 15:39:13 -0500, Charlie Smith wrote: Jim, From info I have located on the internet, I have cobbled together a circuit diagram for illuminating my instrument panel using LED's. I was wondering if I emailed you a copy, would you would be kind enough to take a peek at the circuit and see if I missed anything? Electronics isn't my expertise but I enjoy it all the same. Thanks in advance, Charlie Smith Good grief! I thought rec.crafts.metalworking had a lot of noise... -- Richard Lamb http://www.home.earthlink.net/~cavelamb/ "The clock of life is wound but once, and no man has the power to tell just when the hands will stop, at late or early hour... Now is the only time you own. Live, love, toil with a will. Place no faith in time. For the clock may soon be still." |
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