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Flashing blue LED for HO scale (1/72)

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GarryN

New Member
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
 

evandude

New Member
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...
 

Nigel Goodwin

Super Moderator
Most Helpful Member
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.
 

laroche73

New Member
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):

https://www.reed-electronics.com/ed...=article&articleId=CA223205&rid=0&rme=0&cfd=1

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.
 

crust

Member
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.
 

GarryN

New Member
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
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Re: Thanks for blue LED suggestions

GarryN said:
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

Have a look at https://www.meridianelectronics.ca/gadgets/555/555.html for a really nice 555 tutorial.
 

laroche73

New Member
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 https://www.allelectronics.com/cgi-bin/category.cgi?category=340200&item=LED-72R&type=store in series with a blue T1 LED like this https://sales.goldmine-elec.com/prodinfo.asp?prodid=7031 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).
 

olly_k

Member
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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