LED Police Strobe Question....

[205GTi]

Dear all,

I was asked to make a LED police strobe for a stage production....

But all I know is how to wire up LEDs to light up with the correct current and voltage....

Could anyone please kindly show me how this could be done? I guess it will involve more than a single NE555 wired up together.... 

This is what result I need:

blue flash >> blue flash >> blue flash >>> short pause >>> red flash >> red flash >> red flash ... then cycles

Hope the pic will make it clearer.

Thanks in advance guys!

[justDIY]

a microcontroller is going to be your quickest and easiest (in terms of a circuit) solution ... either the cheap picaxe or the expensive basic stamp should let you get started without any special hardware

other than that, google shows me lots of results for led strobe light circuits... you're going to have to combine at least two timers, one controlling the strobing effect, the other controlling the oscillating.

here's one thought:

1) a 555 astable is setup to deliver your 3 hz flash (looks about 3 hz in the picture) ... this 555 just strobes continously.
2) a second 555 is setup to deliver a 1 hz clock which will run a 4017 counter.
3) the outputs of the counter are connected to your led arrays (via transistors of course) ... the transistors receive their power from the first 555 (via another transistor).
4) as the clock ticks the counter, you could have two "red-on" events, followed by two "off" events, followed by two "blue-on" events, followed by two "off" events, with the tenth counter output connected to the counter's reset pin.  this should give you the pattern of 6 red flashes (in 2 seconds), 2 sec pause, 6 blue flashes and another 2 sec pause.

so you'll need three ICs (2x 555 and 1x 4017), along with a handful of resistors, capacitors, transistors, etc.... if you go the microcontroller route, you'll need the microcontroller and two transistors.

[205GTi]

Thanks JustDIY!

Thanks for your detailed explaination on how this could be done. I totally understand your idea of using 2x555 and 1x4017.... but i will have to look into the wiring then.... I will try looking into that.

How about the microcoontroller? Is there any off the shelf microcoontroller that would do this job? Or am I asking a seriously dumb question as it must be programmed by a DIYer? And what will the wiring look like?

Thanks again for your help!

[justDIY]

yea, i'm not sure about the wiring regarding the discrete components either, it'd be something good for a breadboard.

in terms of the microcontroller, the wiring is simple, you have your chip, you can run it off some AA batteries for saftey and simplicity (it will run many months off a few AAs) ... two outputs from the chip would connect to transistors, these transistors would turn your led bars on and off, pretty simple.

i've attached a simplified version of the circuit ... as far as programming, you should be able to find code examples that do what you want, or close to it, then it's just a matter of copy + paste.   the advantage of the picaxe chips is they program with a simple serial cable... to get into programming real 'hardcore' microcontrollers you'll need a flash eeprom programmer, which isn't all that complicated, but more-so than the simple serial cable.

[Henry455]

If your budget will permit, you can buy LED strobe flashers for under $20.00 that will alternatey flash multiple LED arrays. The one I have has 2 outputs and each output will handle 3 amps each. You can also select the flash pattern you perfer. double flash, quad flash, etc. Most of the strobe lighting internet stores have them. here is one link:  https://www.911lightstore.com/displayProductDocument.hg?productId=922&sourceCode=froogle

[justDIY]

Hello Henry and welcome to the forums!

That's a valid suggestion you have there ... I'm sure if we disected one of those pre-fab flashers, we'd find a microcontroller and transistors.  They probably use a more powerfull uC, to provide a larger choice of patterns, and probably some more complicated switching, to account for high power arrays, reverse polarity protection and such.

Basically it's a 10% hardware and 90% programming composition in either solution.

[Henry455]

 Prior to these LED strobe flashers being available, I did make a homebrew "LED strobe flasher" using 3 555 timers. I had 2 running at approx. 8 hz that drove the 2 seperate led arrays using 2 mosfet power transistors and the third 555 was used to controll the on and off time of those timers. I had it configured to give me approx. 60-70 alternating "quad" flashes/min. Worked extremely well but was a bugger to wire and tinker with to get the timing worked out. Got a home drawn schematic around somewhere if anyone is interested

[justDIY]

Sure toss that schematic up if you don't mind.

I had thought about doing it using 4017 counter(s) and a 555 ... you would arrange different patterns by attaching different combinations of the ten outputs to either the red or blue transistors... it'd be a rats nest of wires!