flasher circuit

[InTheDark]

Does anyone know of a small, simple circuit that i can use to control a flashing LED at really low currents (<5 ma, at a pulse rate of approximately 10 sec). I know there's a 555 circuit or something that can be used, but I need something really, really small, I probably only have room for a few SMT components. Thanks

 

[Jonathan]

Probably the simplest thing that you could do is to find an LED with a built in flashing circuit. The other approach would be to buy the LED body flashers (small units, about the size of a large pill, use SMD LEDs, SMD components, and watch batteries, and stick to things like earlobes using magnets)

Go to digikey and search for LED flash and you will find several components that are standard 5mm housings with flash circuitry built in.

Do a google search for LED flasher and you will see the body flashers.

-Jon

 

[carbonsparky]

Does any one remember the LM3909 flasher chip? You might check and see if any one sells a smd version. You just need a resistor and a capacitor with this chip. It also functioned as a charge pump so you could drive a LED with a 1.5 volt battery. I still have a few of the 8 pin dips around from back about 25 years ago. I used them to make flashers for my flashlights and for driving indicator lights. You can very the flash rate with this chip and drive it from lower voltages than the flashing Leds.

 

[InTheDark]

Hmm...anything smaller than those two options? I've seen those flashing LED's that they use for jewelry, but I think it's still too big. Maybe I should rip one apart and see what the insides look like. I was searching for some flashlight surface mount LED's but I haven't found anything yet. I want something small enough to fit in the tailcap of a maglight, or even smaller if possible.

 

[Jonathan]

Well, it _must_ be possible to build something smaller, but it might require custom silicon packaging. Remember that the chips that you use are small bits of silicon packaged into much larger bits of plastic. If you have the appropriate equipment, you can just work with the _very_ small bits of silicon.

That said, I think that you are looking for a small component or two that you can use. Probably your best bet is to use a computer! Seriously, Microchip Corp. sells rom programmable microprocessors that include the CPU, memory, IO, etc, all in a single package. The smallest is an 8 pin device about 5mm square. Very simply programmed to turn a pin on and off at whatever frequency you desire. You could even measure the supply voltage and change the flash rate to tell you how the batteries are doing.

Take a look at the microchip PIC12F629 or the PIC12C672 or their ilk.

-Jon

 

[billw]

If your battery voltage is high enough to drive your LED, then you can
probably use something like the "solar engine" used by the BEAM robotics
folks (see the BEAM yahoo group, or www.solarbotics.net)

The (discontinued) 3909 LED flasher could drive a 3V LED from a 1.5V
battery, but I don't think there's a modern equivilent.
(I think the 3909 was aimed at exactly the sort of
always-on indicator that you seem to be interested in.)

BillW

 

[LED_ASAP]

The miniMag tail cap has enough room for a not-so-fancy flash module. If you remove the spare bulb, you have almost 8mm ID x 10mm long space. You should be able to build something that fits that space.

 

[InTheDark]

Almost forgot about this subject, thanks for bringing it back up. I found a little flasher circuit, a tiny, one about the size of a SMT resistor. They're in those cheap flashing badges, I have a couple of them from a trade show. The good news is that they're tiny, and very simple. 1 chip, 2 leads to go to the LED, 2 leads to the battery, and 2 to the switch (actually, only 5 leads because the battery and LED use a common ground) It's almost perfect for what I'm looking for, but the only problem is that it flashes too fast and too bright. Don't know anything about the chip, and I've already burned one of them up just playing with it.

BillW, thanks for the link, I'll have to check it out more carefully, but it sounds like the kind of stuff I'm looking for.

LEDmasap,
I wish I had all that room in the original cap, but I'm using a RAM tailcap switch that has the switching mechanism right in the center of the cap. So I'll have to figure out a way to stuff everything inside and still have an operational switch.

 

[INRETECH]

Use the Cyngal F300 CPU; its a ONE CHIP total CPU; about the size of an asprin .15x.15

Takes POWER and GROUND, thats all