Pulsing LED, how to?

[mkruger]

How do you make a LED pulse? I assume I want to do this with some sort of a triangle wave...

-mike

 

[NewYorkDave]

Yes, a triangle or ramp or similar waveform with a less-steep risetime would be preferable to a squarewave (less likely to radiate hash into your audio circuits).

Do a web search on "astable multivibrator" and you'll come up with a million circuit examples. The 555 timer IC is very popular in this sort of application. Although the squarewave output of a 555 astable is the most-often used, there is a ramp waveform available at the capacitor on pin 6.

In many instances, the astable won't be able to source the LED current directly, so you would use it to drive the base of a transistor which would control the current through the LED.

If you can give more details about what you have in mind, we can offer more specific suggestions.

 

[mkruger]

well, I saw my friends Mac go into sleep mode the other day and I liked how the LED was pulsing. I thought I might incorperate this into a preamp I'm making now, while it's in standby. I'll use the 12V power supply.

 

[mkruger]

I think I'll use a monostable multivibrator for a single color LED, but then again it might be cool to use a astable to occilate between two different colors!

The HTC550 is a good chip for this.

 

[CJ]

You can put the led in series place of the collector resistors, or run it in parallel.. This means you can use either one or two led's.

 

[SSLtech]

That mac 'hibernating' LED "slow-breathing" pulse is an extremely clever circuit. I remember seeing it. It's done with a really simple circuit, too IIRC.

...sadly I didn't save the schematic.

Keith

 

[clintrubber]

I don't know if it's about a randomly pulsating LED you're after, but the Oakleysound-site mentions such a thing as a nice side-appilcation of a filtered noise-source:


quoted from http://www.oakleysound.co.uk/noise.htm :

The module also gives a very low frequency output or infra-red signal. This can be heard as a serious of random thumps when listened too, but it is actually a randomly varying output voltage changing all the time, sometimes quickly and sometimes hardly at all. Fascinating to watch when it controls an LED, but it comes into its own when controlling filter cut-off on an otherwise static sound.

Bye,

Peter

 

[mkruger]

[quote author="cjenrick"] so get it while you can.
[/quote]

got it, thanks!

 

[mkruger]

[quote author="SSLtech"]That mac 'hibernating' LED "slow-breathing" pulse is an extremely clever circuit. I remember seeing it. It's done with a really simple circuit, too IIRC.

...sadly I didn't save the schematic.

Keith[/quote]

I think i found it Keith

http://www.rabidhardware.net/files/5/pic2.gif

 

[CJ]

Crap. Please make that 4142 transistor a 2n4124. '
sorry. dislexic draftsman.

 

[mkruger]

[quote author="cjenrick"]Crap. Please make that 4142 transistor a 2n4124. '
sorry. dislexic draftsman.[/quote]

will do....

I think i'll try and build this a few different ways and see how they all turn out.

 

[Svart]

is that an LM1458?

 

[Mark Burnley]

Yep,

1458 dual op-amp. Looks like an op-amp integrator with hysteresis-feedback.

MC1458 dual op-amp Datasheet PDF

Other fun ways to flash LED's:

Simple logic inverter oscillators- check this out for info:

CMOS Oscillators PDF

These are very quick and easy to build, and if you use NANDs such as 4011 etc, you can use a spare input as a "gate" to switch the flasher on and off. You can use an extra gate buffer as a direct LED drive, or a further inverter section for two LEDs in bi-phase. CMOS works down to 3V too, so you can get away with driving LEDs directly.

Nat Sem have LM3909 LED flasher too:

LM3909 PDF

...and I still seem to come back to the trusty (crusty??) NE555 for flash and osc duties- maybe because I just know it so well :roll:

NE555 Datasheet PDF

Mark

 

[CJ]

i forgot, but you can buy blinking LED's at radio shack. no other components needed, just the LED.

 

[Gus]

look for some of the F. Mims III books Rat Shack used to sell some.

 

[Steve Jones]

The LM3909 is the simplest way, it is a chip designed to flash LED's, you just add power and a timing capacitor.

 

[mkruger]

flashers are so common and boring... that's why i wanted to go with a pulsing "breathing" look. Can the LM3909 do this?

 

[Gus]

google for the Kay tremolo circuit schematic effect petal. It uses a twin tee osc that can drive a led in the way I think you want.

 

[Svart]

that 1458 circuit is exactly what you want for the breathing effect.