Looking for best way to Blink/Flash dual LEDs at 3v

Thread Starter

tapir11

Joined May 17, 2017
2
Hi All,

I've got a dummy burglar alarm box that I want to add dual flashing LEDs (probably blue). I'm just getting into electronics and I'm hoping this could be a good first project.

Requirements:
Flash x2 Blue LEDs alternately
Alternate flash every 2 seconds (or similar)
Powered by x2 AAA's = 3v (lithium as they will need to work at low temps and last well)

From some research i've found out:
555's = require more than 3v to operate

Possible solutions:
LM3909
LM393
2N2907
BC548B NPN TRANSISTORS

But I'm not really sure what would work best - any advice?

Many thanks in advance,
 

#12

Joined Nov 30, 2010
18,223
(probably blue)
Not likely. Blue LEDs require more than 3 volts. You're probably stuck at the red end of the visible spectrum.
That CMOS 555 is a good choice and you can use a capacitor in series with each LED to get a quick flash while the timer is taking its sweet time to get the 2 seconds clocked out.
 

crutschow

Joined Mar 14, 2008
29,485
If you really wanted blue LEDs you could use a small inductor flyback circuit to generate a voltage greater than the battery voltage, such as the Joule Thief Circuit.
These circuits can generally operate down to a very low battery voltage, using just about every last bit of the battery energy.
 

Thread Starter

tapir11

Joined May 17, 2017
2
thanks so much for the replies,

R!f@@ - Thanks I was unaware there was a low power version of the 555
#12 - Thanks, Red LED is OK and fine for these experiments
crutschow = Joule thief - very intresting - taking a look.


I've been looking on ebay and found sellers who look to make blue blink units running at 3v
http://www.ebay.co.uk/itm/BATTERY-POWERED-DUAL-FLASHING-BLUE-LED/141187128847

I'm temped to buy one to take apart to learn - there looks to be very limited number of components?
 

#12

Joined Nov 30, 2010
18,223
These circuits can generally operate down to a very low battery voltage,
I ran a Joule Thief to its limit. It will start up if you have at least 0.6 volts and it will suck a battery down to 0.3 volts if it's already running.
there looks to be very limited number of components?
A joule Thief isn't any more complicated than a crystal radio but it uses a magnetic coupling which is about 9th on the list of what beginners might get around to studying.
 
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