Way, Way, way OT How to make an LED blink every 30 seconds?

[javacody]

Is there some easy way to make an LED blink every 30 seconds?

[ExpAnonColin]

An astable multivibrator tuned to 1/30hz would work perfectly, I believe.

-Colin

[Leftrights]

There are also IC's that are designed to flash LED's.  Craig anderton uses them in a little circut to save batterys.  I'll see if I can find the # for you.  It would probably have the least off board comp.s`

[javacody]

Colin,
  That sounds like something I would buy in an "Adult Bookstore". What the hell is an astable multivibrator?  

[niftydog]

What the hell is an astable multivibrator?

get your mind out of the gutter... at least while you're visiting this website!

google will tell you all you need to know.  Suffice to say that an astable multivibrator is a sort of an oscillator.

The cheap solution is to use a 555 timer chip.  For you yanks they should cost as little as 40 cents each if you buy them from the right place!  Add a couple of resistors and capacitors of the right value and bobs your uncle!

[Leftrights]

the IC that I was talking about is the LM3909.  This would probably be your best bet as there's not much to do to get it going.  The only thing I'd double check is that you could get oscilations (I can't spell) that slow.

For reference a multivibrator is not only fun to sit on it's also a logic element with two states.  In other words the output is either - on or off -   -high or low-  -one or zero-... you get the idea.  when the logic is high your LED is on, when it's low LED is off.

The "astable" part of the name tells you this  :arrow:   that it will change states, from on to off, indefinatly.  In other words being on will turn it off and being off will turn it on.  This gives you a sqaure wave.  That will make your LED blink.

if you are interested in this kinda stuff  you could google "monostable multivibrator"  and all the other multivibrators out there.  Just try to ignore all the hits you get for   ****GARY"S XXX HOUSE OF ASTABLE MULTIVIBRATORS ----- BIG TITTIES AND ONE SHOTS*****

[Peter Snowberg]

The low current solution is a chip called the LM3909. They used to be sold at RadioShack back in the good old days. It's really made for low voltage, but you could adapt it to anything.

Take care,
-Peter

[Rick]

I agree with Peter that one of the best solutions is the 3909 led flasher chip. It's very low current and low voltage (I've had a fake alarm circuit blinking for over a year with a 1.5v D cell battery).
You can also build a very simple flasher with two transistors and a couple of resistors / caps. Do a Google search on led flasher / timer - circuit.
You can experiment and learn with cap / resistor values for the timing cycle.

[cajununicorn]

javacody,  you could just pay a wino 2$ to flip a SPST every 30 seconds and shock him if he doesn't do it right.....
just kidding!  :lol:

[amz-fx]

The cmos version of the 555 should be about as low power as the 3909, easier to find and more versatile.

http://www.haunted.50megs.com/props/eyes/circuit.html

..or for a transistor circuit, look at the last one at:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm
or
http://www.reprise.com/host/circuits/transistor_flasher.asp

Here's the 555 timer calculator;

http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm

regards, Jack

[petemoore]

I think I missed the application for the 30 sec interval blinking LED...just curious what one could use that for...

[sirkut]

The lm3909 IC has been discontinued plus if you wanted it to blink every 30 seconds, you'd need a larger value capacitor.  Search google for "led flasher lm3909" and you will find a schematic.  If you can manage to find that chip, play with cap values.  Otherwise I'd suggest using a 555.

[javacody]

Well, the blinking eyes circuit Jack linked to above would be cool on a Fuzz Face.  

I read about a device for losing weight based on the philosophy of mindfulness. It has an led that blinks every 30 seconds and is seed shaped (and called the Seed, imagine that). Anyway, I was thinking this would be simple to do but wondered how you would do it. Thanks for the education guys!

[AL]

The LM3909, while a handy little guy, has been discontinued and is VERY pricey (if you can find one) approx $6 on the low end from what I was seeing a few months ago.

NTE does make a replacement.  However, it ain't cheap either. I can't remember the # but at one time Web-tronics had it listed on their site for around $3.  When I called them they said they were out but I called NTE and they had recently "found" several.  So web-tronics may have it in stock at this time or you can tell them to call NTE.  But ask them for the price first.  This chip is very pricey at Mouser and in my opinion really not worth it.


AL

[javacody]

How many volts would an astable Multivibrator take? It seems like the 555 option can run off of 1.5 volts.

[idlefaction]

is the timing critical?  cos if you're running an astable multivibrator at 0.0333Hz, the leakage and bad value tolerance (are they still +/- 20%?) of the electro cap you'll have to use will come into play.  :/  you could do the maths perfectly, and end up with a circuit that blinks an LED every 35 seconds...

[AL]

This may help.

http://www.meridianelectronics.ca/gadgets/555/555.html

AL

[Hal]

depends on the bias of the transistors, or the requirements of the op-amp ?

you could probably build one off 1.5v

[ExpAnonColin]

Depends on what your LED needs, and what the transistors need.  I'm glad my suggestion is generally accepted, though.  Idlefaction was way right in saying that the timing is probably going to be quite a bit off of 30 seconds, unless you use uberexact components.

-Colin

[javacody]

Thanks for all the help guys. I was thinking that I would use a pot to dial in the resistor values, and I have 1% metal resistors so hopefully I can get pretty close.

That 555 tutorial looks like exactly what I need, thanks AL!