Hello guys,

So my dad has a retail store and he was going to buy something from someone that makes the sign flicker. thing is that it was 500 dollars!

i am in a circuits class and i was thinking that i can use either an OP-AMP or a function generator. and my friend said that i can also use a 555 timer for this. my problem is that i know how to change the frequency of the sign using the function generator since i just turn the dial left or right. but how can i do this using an Op amp or a 555 timer. also my friend suggested that i shouldnt buy a function generator because it can do way more than what i need, and that it would be a waste of 200 dollars if i buy one just to flicker a sign.

any suggestions guys?

 

LEDs, 555s, Flashers, and Light Chasers

Chapter 12, Special Effects, Fire!

 

can a 555 timer operate/handle a 120 V AC source?

 

Nope, but neither can op amps. What is your experience level with electronics?

You will need a low voltage source, such as 12VDC or 24VDC.

Before we continue, please read the article, it is pretty obvious you haven't.

 

A little more information on the sign would be helpfull, AC 120?, flourescent[ ouch] size? A bunch of white LEDs flickering via PWM using a flickering candle LED works great- from a recent post on AAC. I tried it with a 200000 mcandle white LED - looks great- in process of converting an outside pole lamp with bright yellow LEDs.

 

I made an LED controller for a sign that they wanted to flicker like an old Edison light bulb. I used a PIC microcontroller PWM periperal and a couple of MOSFET's to control the LED banks. That way I could program, in C code, the pattern I wanted then change the pattern and speed based on the customer's feedback. I think it had about a 7 second repeating pattern of on/off and various levels of fadeup/down and flicker. Let me know if you want any of the info on how that was hooked up. There's a video here http://www.youtube.com/watch?v=zz_RiLE5HbQ but it doesn't really show the flickering that great.

 

Found this: http://www.discovercircuits.com/dc-mag/Issue_nov10/pg-4.htm " Flickering Candle" yellow LED with lens, # G17848, $ US 1.49, Electronic Goldmine.

 

Interesting, I hadn't run across those before. I question the 2V Vf yellow LEDs a little though, I'll be checking them out too.

 

Had another thought: 3 or 4 parallel load shift registers, a 555 clock, driver, 0-crossing triac opto-coupler, triac, & dip switches to load SR. Load a pseudo random pattern into SRs, clock pattern out of serial out thru buffer into opto coupler & TRIAC. Last stage feeds back to serial in. A countr can re-load every few cycles to add even more randomness. IF a more suttle effect is desired, use SCR shunted with a diode, so that light, assuming 120V AC or similar,never goes completely out.

 

yes i have read the articles lol, just not deep enough ill look at them again

im taking a circuits class right now. (studying electrical engineering )

it is an LED sign composed of about 1000 LED's (not quite sure gonna ask my dad when i get home on the weekend) and it is powered by a 120 V AC source

thanks for the posts

 

LED circuits are powered by DC. You need a power supply, this is a pretty standard convention. Personally I lean towards wall warts, they are both cheap and safe. If you want to make a power supply from scratch that is an option, but it is not cheap or as safe.

Like I said before, this is true of all solid state electronics. When you mentioned AC it threw me a bit. I was not aware of the flickering LEDs, I will have to experiment with them myself to see if they really flicker. They sound like a good option.

I have other options published, which you use is up to you. I am one of the local draftsmen/designers on this site, I draw a lot of ideas (untested a lot of them) for other people. While untested, the odds are very good they will work, as they are based heavily on prior art.

If you are getting into electronics you might as well get used to a lot of reading, and if the comprehension didn't stick, rereading. The article I wrote is fairly basic electronics.

 

Hello,

If you want to power leds, you MUST use an isolated powersupply.
If you want to run it from the mains directly, you will violate the rules and the thread will be closed.

Bertus

 

Someone put up a suggestion of high voltage LEDs, which will get this thread closed through no fault of the OP. If the OP had done this it would have been closed.

There is never any reason to use AC for LEDs, since they are low voltage DC components. You can do anything you want with 24V on LEDs, and there are some very inexpensive power supplies out there to do it with (6A 24VDC will power 2,000 LEDs or more).

Whatever scheme the OP chooses I will be glad to help out with.