Flashing blue LED for HO scale (1/72)

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GarryN

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I wish to have a flashing blue light on top of a 1/72 scale police car. Power can be external but really electronics need to be internal. No room for circuit boards (car around 33mm long)! Is there some small in-line electronic 'flasher' that would work with a 3mm blue LED to simulate a police light please? Also, if possible, a good UK source of LEDs and components.

Thanks for any suggestions
 
one thing you could try is putting the LED in series with a flashing LED that's been dipped in paint or something... I have heard that the circuitry in the flashing LED will cause all other LEDs in series with it to flash as well...
 
Well Maplin do a 5mm flashing blue LED, order code N65AJ, but don't appear to list a 3mm one. They do list 3mm standard LED's though, you could easily flash one with a 555 timer, or even a simple astable multi-vibrator.
 
power source?

What were you planning to use for your power source? White & blue LEDs have a higher forward voltage drop than red or green LEDs, typically in the 3.4V - 4V range. The blue flashing LED Nigel mentioned is probably your best bet, but requires 5V-14V. Two small rechargeable lithium (3V) batteries in series would work.

Alternatively, you could try adapting a circuit like this to work off a single coin cell (it's a white/blue LED driver design, not a flasher):

**broken link removed**

The circuit could be miniaturized using all SMT components, but the inductor would be a problem. Another possibility is a charge-pump IC, some work with small-valued caps. It's a tradeoff, either your power supply takes up the space, or the drive components do.
 
I would opt for the stand-alone blue led and then a small circuit to blink it. Perhaps a 555 and a handful of discrete parts. Alternatively, you could build it entirely out of discrete components. This is unless of course you can find a 3mm blinker.
 
Thanks for blue LED suggestions

Thanks to all the responses. It is intended for model railway use, so voltage up to 15V is available. However a locally placed battery would be fine as it would have a long life I guess that it would be even easier to keep the electronics with the battery - something that I hadn't considerd - and leave the clever stuff until later. 5mm LEDs would be about scale 15" across which, although simpler, would look out of place. An in-line flasher would still be nice but a 555 seems to be an answer. Is there a circuit posted that will enable me to calculate the components needed.

Thanks

Garry
 
Re: Thanks for blue LED suggestions


Have a look at **broken link removed** for a really nice 555 tutorial.
 
flashing LEDs

Hi Garry, if the power source isn't a problem, then evandude's suggestion is probably the tiniest solution and gives the lowest component count.

Wiring a flashing LED like this http://www.allelectronics.com/cgi-bin/category.cgi?category=340200&item=LED-72R&type=store in series with a blue T1 LED like this **broken link removed** should work. I assume you'd hide the non-blue blinking LED somewhere (Don't forget to include a series current-limiting resistor if you're going to run off 15V).
 
Shame the lm3909 isn't available anymore cos I have falshed a blue led off that before....
type lm3909 equivelent circuit into google to see what comes up?

--OR--

how about using a peice of fibre optic cable, and some kind of light diffuser / trap to add to the top of the car??? You can get that really thin fibre from one of those novelty lights or even model shops?? - that way you could have the led UNDER / in the car and things may look a bit better scale-wise as well! You could also feed more cables off the same led or though I think would look odd with lights flashing in sinc everywhere! With some imagination in the circuit you could also have a more realistic flash effect?
 
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