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Windows 7: LED Dimming and Brightening

29 May 2010   #21
smarteyeball

 
 

Quote   Quote: Originally Posted by A Guy View Post
LEDS can be dimmed, but I'm not sure this is true of ALL LEDS. The LED's intensity can be determined by the level of voltage being supplied.
As does happen when I increase / decrease voltage to my LED fans.

Sorry LB - not helpful for your scenario.


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29 May 2010   #22
Dwarf

Windows 8.1 Pro RTM x64
 
 

As far as I am aware, the only way to dim LEDs is with PWM (Pulse-Width-Modulation).
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29 May 2010   #23
A Guy

Microsoft Community Contributor Award Recipient

Windows 7 Home Premium x64 SP1
 
 

Quote   Quote: Originally Posted by archie123 View Post
ill ask again just incase.........do you have the led conneted in series with the variable resistor? if you dont it wont work because of the way leds handle voltage and current

just incase your wondering why im spouting all this nonsence ive been an electrical engineer for 20 years and have dabbled quite alot in electronics
Well then, looks like archie123 is your man

A Guy
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29 May 2010   #24
Lordbob75

Windows 7 Ultimate x64, Mint 9
 
 

Quote   Quote: Originally Posted by archie123 View Post
ill ask again just incase.........do you have the led conneted in series with the variable resistor? if you dont it wont work because of the way leds handle voltage and current

just incase your wondering why im spouting all this nonsence ive been an electrical engineer for 20 years and have dabbled quite alot in electronics
Archie, I will be learning about that stuff next year (EECE).

If by in series you mean the potentiometer connects to the LED, then yes.
I have the 12V in hooked up to the first 2 prongs of the pot, then the LED (with 500Ohm res) in parallel with the fan, both connected to the 3rd prong.

I know that they can be dimmed with lower voltage, but I think you are right, it is just not enough of a difference. At this point, I think I will be leaving the LED as is (it does SLIGHTLY dim, not noticeably), because the knob has as indicator arrow. I may even skip the LEDs for now as it doesn't quite fit with how I have everything laid out.

~Lordbob
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29 May 2010   #25
WindowsStar

Windows 7 Enterprise (x64); Windows Server 2008 R2 (x64)
 
 

Quote   Quote: Originally Posted by A Guy View Post
Quote   Quote: Originally Posted by WindowsStar View Post
If you are talking about LED back lighting on LCD TVs they don't dim them.
No, was more an offhand remark. But LED's can be dimmed.

I do believe it has to do with getting the voltage down far enough to allow the led to dim. Perhaps experiment with more resistance until you find the correct amount to allow a dim LED at lowest fan setting (or lowest you will actually turn it down to, lest higher than complete lowest again gives you a bright LED), and brightning at the full brightness voltage. It may well be that the voltage difference between dim, and full bright may be too small a difference for you. A Guy

Did some googling:

LED Dimmer

Starts getting into building a circuit, and finding the right parts.
Good find:

If you note my post above I showed how to dim LEDs. You need HE-LEDs to make it work, but the OP was looking for a simple way to just dim the LED with a POT, which is not going to work so I suggested a bulb. Replacing the LED with a simple RED bulb will make everything work without adding anything to his design.

The dimming link you provided: I don't think will work the way the OP wants it to. With a lot of LEDs it may sort of dim, remember LEDs are really an ON or OFF device, the graph on your link even shows that. (I would have to build circuit from your link and check how well it works) But using a transistor is not a very good way to dim the LED it will produce a lot of heat. Again pointing to the LED dimmer links I posted will dim the LEDs. It works by pulsing the LEDs with a 555 timer chip. Since we cannot see the LED turning ON and OFF the longer OFF time makes the LED look dim. I have built this circuit before many years ago and it does a good job, I would not say great because the LEDs will turn off at some point and they did not look very dim. Using the bulb makes the circuit simple without the need for the timer chip and extra space.

Great post, great options, let’s see which way LordBob goes.
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29 May 2010   #26
Lordbob75

Windows 7 Ultimate x64, Mint 9
 
 

Quote   Quote: Originally Posted by WindowsStar View Post
Great post, great options, let’s see which way LordBob goes.
Quote   Quote: Originally Posted by Lordbob75 View Post
I know that they can be dimmed with lower voltage, but I think you are right, it is just not enough of a difference. At this point, I think I will be leaving the LED as is (it does SLIGHTLY dim, not noticeably), because the knob has as indicator arrow. I may even skip the LEDs for now as it doesn't quite fit with how I have everything laid out.
~Lordbob
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18 Apr 2011   #27
DrToxic

Micro$oft Windows 7 Ultimate x64
 
 

excuse my reviving an old thread, but LEDS can be dimmed, and in the fassion LordBOB wants.

for proof, a quick experiment, get one of the POTS, and a cheapo LED FAN from somewhere (That connects VIA molex 12v)

watch how the three LEDS dim when you turn the POT down, and brighten as you turn it up.


Maybe (this might be a slight messy, but) you could take one of those cheapo fans, fit it, put an extention on one of the three LEDS, and put that up front of the case? - dimming LED

or put all three leds up front and use them to surround the knob?
phunky
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18 Apr 2011   #28
Lordbob75

Windows 7 Ultimate x64, Mint 9
 
 

Quote   Quote: Originally Posted by DrToxic View Post
excuse my reviving an old thread, but LEDS can be dimmed, and in the fassion LordBOB wants.

for proof, a quick experiment, get one of the POTS, and a cheapo LED FAN from somewhere (That connects VIA molex 12v)

watch how the three LEDS dim when you turn the POT down, and brighten as you turn it up.


Maybe (this might be a slight messy, but) you could take one of those cheapo fans, fit it, put an extention on one of the three LEDS, and put that up front of the case? - dimming LED

or put all three leds up front and use them to surround the knob?
phunky
I tried this, and it had no noticeable effect on the LEDs. The only way it would really work is with PWM.

~Lordbob
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 LED Dimming and Brightening




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