Ryan Harding

What is the way to make an LED, (green), 'flash, using 2x1.5v power supply.
The thing im looking for is it HAS to made into the smallest possible circuit as i need it to fit in a small slot.

So far i have one using a 555 timer chip. Its too large and not what im looking for.

Thanks in advanced

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TillEulenspiegel

You can buy a LED that has a flasher circuit encapsulated in it.

trippy_zippy

maplins have them m8 item number N65AJ, they have various sizes too

laroche73

The only trouble with self-contained flashing LEDs is finding one that runs off of 3V (those from Maplin take a 9V supply). Is the size of your power source an issue as well, or is it only the size of the flasher that matters?

For flashing circuits, it's hard to get much smaller than a 555 in surface mount, the timing cap is probably the largest component. You can browse through some more flasher circuits here

http://www.discovercircuits.com/L/lite-flash.htm

There was also a thread a while back on a similar topic

http://www.electro-tech-online.com/v...602&highlight=

Roff

All Electronics has 3 volt flashing green LEDs.

Exo

The smallest possible, a pic10F with a little program to make it flash...
SOT23 size...

laroche73

Very cool Exo, hadn't seen that yet. Internal 4Mhz osc, lots of possibilities for miniature circuits. Too bad one of the pins is input only, 4 full I/Os would be nice. Still, it's a lot of power packed into a tiny SOT-23 package.

http://ww1.microchip.com/downloads/e...Doc/41239A.pdf

Edit: update 6/17/04 - I asked uChip tech support about the I/O count and got a quick response. "It has to do with the input structure for this pin, which also doubles as external MCLR#/Vpp; a design trade-off was made to keep the cost of the device down. "

My beef was that with 4 I/Os, you could drive up to 12 LEDs using the complementary LED drive method (aka n-connectedness, n^2 - n), vs. only 6 LEDs with 3 I/Os. Driving 12 LEDs from a single SOT-23 package would be impressive.

olly_k

What you want is a LM3909, a dedicated LED flasher in a 8 pin DIL, with only one capacitor required. All this works off 1x1.5v battery, and will typically flash an LED for about 8 months Trouble is they seem to be a little hard to find these days...

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OLLY_K

olly_k

Just found this if you are interested...
http://home.cogeco.ca/~rpaisley4/LM3909.html

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OLLY_K

laroche73

substitute "impossible"

I agree Olly, it was a very nice design in it's day . The original app note from NS is brilliant. Maybe someone knows where to source a SMT version of the LM3909? An old rule of thumb (US), if you can't find it from Digi-key, find another part. They run a good business, and source parts that get used. Not to mention NatSemi discontinued this one several years ago. Yes, it's a chicken and egg argument, follow it if you want a safety margin. Digi-key saved my butt at crunch time more than once, loyalty naturally follows.