breathing led?

Printed From: the12volt.com
Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=122311
Printed Date: May 08, 2025 at 6:14 PM

Topic: breathing led?

Posted By: asiansensation7
Subject: breathing led?
Date Posted: June 15, 2010 at 1:03 PM

Hey everyone, new guy here. Not new to car electronics and wiring, but definitely still learning. Anyway, I'm wiring up a push button start system into my car, and would like to do a "breathing" effect with the LED under the button itself. Like how a computer status indicator fades in and out when it's on standby. I found this video for a very simple circuit that runs on 6 volts:

https://www.you tube.com/watch?v=Klengns3oQg

My question is: would any of the components in this circuit have to be changed to compensate for a 12 volt circuit in my car?

Or is there a simpler way to accomplish this effect with a circuit that's already built?

Thanks!

-Jerry

Replies:

Posted By: awdeclipse
Date Posted: June 15, 2010 at 8:30 PM

You could reduce the voltage via the properly sized resistor or you could use a DC-DC converter to get to 5-6 volts. Search for 7805 for the DC-DC converter, they are common and even RadioShack should stock them.

I had trouble viewing the link.

Posted By: asiansensation7
Date Posted: June 16, 2010 at 12:52 AM

Sorry for some reason it put a space between "you" and "tube" in the link. Let's try again:

https://www.you tube.com/watch?v=Klengns3oQg

Anyway here are the parts:
555 timer chip
npn transistor
220 microF capacitor
10K potentiometer
LED

Schematic:
posted_image

I'd think the potentiometer would vary the resistance in the circuit, so it's good to go?

Thanks!

Posted By: oldspark
Date Posted: June 16, 2010 at 4:12 AM

That will run on 12V too.

But the pot at low resistance could blow the 555 timer.
IE - if pin #3 to 0V or 6V goes under 30 Ohm, or 60Ohm @ 12V.. Pin #3 is usually limited to +/- 200mA; hence include (say) an 82 or 100 Ohm resistor from pin #3 to the pot.
You might want to add a 270 or 330 Ohm resistor in series with the LED to limit its current...