Adjustable LED Strobe Circuit

Hello,

I am new to this forum, as well as being new to circuit design, and I apologize if my question is indicative of either ignorance of posting protocol or elementary circuit design.

I'm hoping to build a circuit that can power an array of 24 LEDs in three sections of 8 LEDs each. I want the LEDs to strobe, and I hope to be able to adjust the frequency with which they strobe (much like a common dance strobe light). I assume they would spend half of their time on, half off, with an adjustable cycle between the two states. The whole circuit can be hooked up to the wall, presumably with a DC adapter in-between.

I've looked at a few posts on this site, notably me_guitarist's "LED strobe" and olof102's "Building a 12v Stroboscopic Circuit", and have a general sense of the components that will be incorporated. I presume the design would include a microcontroller, and if some potentiometer could be interfaced to the microcontroller, I imagine the rest would be a matter of programming.

As a potential start, could I modify a cicruit such as FvM's "LED Strobe",http://picprojects.org.uk/projects/images/Ledstrobe.png, to include 23 additional LEDs in parallel, as well as a potentiometer interfaced to the microcontroller?

In any case, I am very flexible with components and input power, as I have a pile of DC adapters that can put out between 5-24 volts, and will be ordering the rest of the components (LEDs, resistors, microcontroller, etc.) after having decided on a design.

I would be very grateful to anyone who could lend a bit of their time to advise me in this project, and though I can offer little technical expertise in return, I can certainly offer my sincere thanks.

Best,
Ethan Beal-Brown

Added after 17 minutes:

Soon after posting my thread, I noticed another thread that may be relevant, GSE's post "circuit for a protable strobe light".

I'm afraid I don't know much about "astable multivibrators" beyond what is mentioned in that thread and on Wikipedia's page http://en.wikipedia.org/wiki/Multivibrator, and I don't quite know beyond generalities how I would go about implementing one into my proposed circuit.

Anyway, I thought this additional thread might be instructive, at least to whoever might be able to help me.

Thanks!

Well I am not an expert but I think you can use 555 timer circuit in astable mode to generate the strobe for LED's. Microcontroller really required here?

I am attaching some theory and pspice simulation results which can help you understand the 555 timer operation in astable mode. Even if your are not using 555 go through this to help u with the astable oepration

-Hemanshu

Thanks! I was beginning to get concerned I'd have to build my own astable multivibrator from individual components! The 555 Timer in astable mode seems like a good solution, but I wonder about two things:

1) I notice that the 555's Output is only capable of 200mA, which I assume means I wouldn't be able to directly power my 24 LEDs if they have a 20mA draw each. This isn't too much of a problem if it isn't the case, as my design is flexible, but I wonder if I'm overlooking something, and it would be nonetheless possible to power more LEDs.

2) Is it possible to add the option of dynamically adjusting the duty cycle, or by extension the frequency the LEDs flash? Under "Astable operation", in the section of the report you sent me discussing the frequency of oscillation, it is suggested that by selecting R1 and R2, the duty cycle can be adjusted, as well as by bypassing R2 with a signal diode (D1N4148). Could some other component replace R1 and R2, and the diode such that the duty cycle is adjustable?

Thanks!

555 can source or sink 200mA of current. You want your all 24 LEDs to be ON at the same time? I guess not. There are LEDs which consume less than 20mA current..just explore...

There are somef combinations you can do to adjust the duty cycle. eg placing a diode across R2, making R1 fixed and using adjustable resistor for R2 can help you.

or just make sure what frequencies you want and according connect the appropriate R (give options of connecting say 2-3 resistance in place of R2) in circuit by just shorting.

Basically using variable resistors in place of R1 and R2 will do you the trick.

If you want to change the frequency at which these high and low pulses are occurring then use 555 as voltage controlled oscillator.

Alright, thanks abbeyromy. I think I can research the 555 timer and look for other circuit designs online that might be pertinent. Thanks for your help!

youa re welcome. using 555 will definitely save you some money