Slow Turn On Led

hernanstafe · 1st May 2007, 03:58 AM

I'm doing a lil souvenir and i need to make a LED turn on and off slowly, but i can't find any schematics to do that...any ideas? i can turn it off slowly by using an electrolytic cap but it' not too nice so i was wondering if there's an ic to do that?

OzMikeH · 1st May 2007, 04:26 AM

two ways:
Pulse width modulation.
or
use a filament lamp instead.

gmphadte · 1st May 2007, 06:48 AM

u need a triangle wave generator.

Gajanan Phadte

Nordic · 1st May 2007, 08:31 AM

there is a 1.5v led driver ic, it is obsolete, but stil available...

Will have a look for the number... Also there is a 2 transistor led flasher circuit I have been playing with, trying to miniaturise for a friend, which flashes the way you want ---- when the battery gets flat...

try Hi brightness LED wich requires more current.... it will allready slow down things....

Nordic · 1st May 2007, 08:42 AM

LM3909

http://www.redcircuits.com//Page87.htm

cpemma · 1st May 2007, 11:13 PM

I'm not quite clear with your requirement - is this a fancy power indicator that fades in (or out) just once on power-up (or down) or a novelty item doing a continuous cycle?

For the former, the simple way is two resistors between power and LED with an electrolytic cap (470uF?) to ground from the mid-point. To get an effective fade keep the maximum LED current to about 2mA, so from a 12V supply the two resistors would be about 2.4k each. This always applies when trying to fade LEDs - ignore all supplier "specs" telling you to use 20-30mA and start from an off-peak brightness.

For a continuous throb, see the two here.

1st May 2007, 03:58 AM	#1
hernanstafe diyAudio Member Join Date: Feb 2007 Location: Argentina	Slow Turn On Led I'm doing a lil souvenir and i need to make a LED turn on and off slowly, but i can't find any schematics to do that...any ideas? i can turn it off slowly by using an electrolytic cap but it' not too nice so i was wondering if there's an ic to do that?

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1st May 2007, 04:26 AM	#2
OzMikeH diyAudio Member Join Date: Mar 2007	two ways: Pulse width modulation. or use a filament lamp instead.

1st May 2007, 06:48 AM	#3
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	u need a triangle wave generator. Gajanan Phadte

1st May 2007, 08:31 AM	#4
Nordic diyAudio Member Join Date: Sep 2005	there is a 1.5v led driver ic, it is obsolete, but stil available... Will have a look for the number... Also there is a 2 transistor led flasher circuit I have been playing with, trying to miniaturise for a friend, which flashes the way you want ---- when the battery gets flat... try Hi brightness LED wich requires more current.... it will allready slow down things....

1st May 2007, 08:42 AM	#5
Nordic diyAudio Member Join Date: Sep 2005	LM3909 http://www.redcircuits.com//Page87.htm

1st May 2007, 11:13 PM	#6
cpemma diyAudio Member Join Date: Jul 2003 Location: S Yorkshire OK	I'm not quite clear with your requirement - is this a fancy power indicator that fades in (or out) just once on power-up (or down) or a novelty item doing a continuous cycle? For the former, the simple way is two resistors between power and LED with an electrolytic cap (470uF?) to ground from the mid-point. To get an effective fade keep the maximum LED current to about 2mA, so from a 12V supply the two resistors would be about 2.4k each. This always applies when trying to fade LEDs - ignore all supplier "specs" telling you to use 20-30mA and start from an off-peak brightness. For a continuous throb, see the two here.

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