Dimming LEDs

[Simon Griffiths]

Dear All,
I am currently building an art project but cannot seem to
get my LED's to dim properly. I have tried capacitors but to no avail. I've
heard that diodes could dim the LED's but I would like the lights to dim
slowly on and off. Thanks for any tips.

Simon Griffiths.

 

[Jonathan Kirwan]

On Thu, 21 Jul 2005 21:11:19 +0000 (UTC), "Simon Griffiths"
<sjg_18_@btopenworld.com> wrote:

I am currently building an art project but cannot seem to
get my LED's to dim properly. I have tried capacitors but to no avail. I've
heard that diodes could dim the LED's but I would like the lights to dim
slowly on and off. Thanks for any tips.

One way is to PWM the LEDs, with the modulation rate being at or above
60-80Hz.

Jon

 

[Byron A Jeff]

In article <dbp31n$8a9$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com>,
Simon Griffiths <sjg_18_@btopenworld.com> wrote:

I am currently building an art project but cannot seem to
get my LED's to dim properly.

Dimming LEDs by changing voltage or current is a black art.

I have tried capacitors but to no avail.

Black art.

I've heard that diodes could dim the LED's

Um. LEDs are diodes.

but I would like the lights to dim slowly on and off. Thanks for any tips.

Now you need an active component in addition: a triangle wave generator.
You can find a circuit by clicking I'm feeling lucky on Google with
the phrase triangle-wave generator circuit.

The third link under 'LED dimmer' which goes to Mike's flight deck has
both the theory and the circuit of LED dimming.

Good luck.

BAJ

 

[ehsjr]

Simon Griffiths wrote:

Dear All,
I am currently building an art project but cannot seem to
get my LED's to dim properly. I have tried capacitors but to no avail. I've
heard that diodes could dim the LED's but I would like the lights to dim
slowly on and off. Thanks for any tips.

Simon Griffiths.

Go here: http://ourworld.compuserve.com/homepages/Bill_Bowden/
Look for "fading red eyes" .

Ed

 

Byron A Jeff wrote:

In article <dbp31n$8a9$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com>,
Simon Griffiths <sjg_18_@btopenworld.com> wrote:
I am currently building an art project but cannot seem to
get my LED's to dim properly.

Dimming LEDs by changing voltage or current is a black art.

I have tried capacitors but to no avail.

Black art.

I've heard that diodes could dim the LED's

Um. LEDs are diodes.

but I would like the lights to dim slowly on and off. Thanks for any tips.

Now you need an active component in addition: a triangle wave generator.
You can find a circuit by clicking I'm feeling lucky on Google with
the phrase triangle-wave generator circuit.

The third link under 'LED dimmer' which goes to Mike's flight deck has
both the theory and the circuit of LED dimming.

Good luck.

BAJ

LED dimming by current control (analog) is hardly a black art. For
simple dimming, a voltage controlled current source with sufficient
compliance would work fine.

http://www.national.com/ds/LM/LM101A.pdf#page=11

The top of page 12 of this shows a bilateral current source which would
work if you limited your control voltage to the correct polarity.

5 years ago I did a prototype linear LED controller using a now
discontinued Burr-Brown SHC615 driving the LED and sourced with 15KHz
to 30MHz analog video to test photosensor/preamp assemblies. It worked
very well.

You can do this with one opamp.

GG