Flasher Chip Search

[HarryN]

Hi, I am looking for a simple device that could be put "in series" with a small LED to make it "flash / blink". Current flow would be approx 20 - 50ma - enough to drive a 3mm or 1206 size red LED.

I am looking for something simple, but rugged. The ideal size would be nominal 3mm long x 2mm wide or narrower (1206 size for instance)

The alternative would be if I can find a similar size RED LED which already flashes. Frequency is not a big deal, just so it blinks. 5mm is too large, but 3mm or 1206 size are ok.

Thanks HarryN

 

[WildRice]

I think I have a couple 3mm flashing LEDs. PM me if you need 1.
Jeff

 

[HarryN]

Thanks Jeff - I am actually looking for a few more than that - you know how it gets when you start playing with flashing leds.

 

[Bill]

Allelectronics has a number of flashing LEDs:

http://www.allelectronics.com/cgi-bin/category.cgi?category=340200&type=store

 

[xochi]

They givem out by the gazillions in bars and nightclubs as little flashing beercap buttons

 

[HarryN]

Thanks everyone - I am surprised that there are no in line chip solutions around. Seem like there must be something like that available somewhere.

 

[Steelwolf]

The simple industry solution used to be the LM3909 chip, which not only provides flashing, but also works as a charge pump. This is most commonly found in those red rear lights for bicycles. Just one chip will drive a huge line of LEDs. I heard it became obsolete, but I'm not sure what it was replaced with.

Other solutions would be to use a 555 chip which can give you an astable flip-flop. So you can drive 2 lines of LEDs, one line with a certain on-off time and the other line will be the direct opposite.

But I suspect that what you really want is a random sort of pattern, where each LED decides to switch on or off on its own. In which case, your simplest solutino is to head to the shops (online or otherwise) and look for blinking LEDs. These already have something inside that blinks the LED. And the LEDs aren't much more expensive than their non-blinking counterparts.

I'm not sure about an external discrete solution that would give you a similar effect. The chip that switches the LED on and off will need a continuous power supply to it, so at the very least, you will have 2 wires going to the chip, and 2 coming out from the chip to connect to the LED. It will not be truly in-line.

 

[HarryN]

I actually am just trying to run one, low power LED. It does not need a random pattern, any pattern of on/off will be fine.

My analogy is the very simple concept of a Xmas light bulb going on and off by itself. I assume that the incan versions use some sort of fuse / thermal arrangement.

 

[Steelwolf]

HarryN: I thought you wanted more than one since you asked for more than the few that WildRice had. That link to All Electronics that Bill posted shows a bunch of good stuff.

Incandescent versions will either use modern electronics, which means basically a 555 astable circuit with FET switchers to handle the higher voltages and currents, or the really old method of a bimetallic strip. I saw one of those in a Datsun 120Y once. That's a car that was produced roundabout 1970.

Apparantly, the strip will heat up if current passes through it. Being bimetallic, the bits will expand at different rates, causing the strip to curl and bend away from the contact thus breaking it and allowing the strip to cool down and straighten enough to retouch the contact.

If you can find that, I'm sure you can adapt it for use with LEDs.

 

[HarryN]

[ QUOTE ]
Steelwolf said:
HarryN: I thought you wanted more than one since you asked for more than the few that WildRice had. That link to All Electronics that Bill posted shows a bunch of good stuff.

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Sorry for not being more clear - yes, I do want to make a number of these, but each driver / on / off control chip will only be hooked to one LED.

I did look at the link - yes they do have a number of flashing LEDs. I have seen similar - but once again, perhaps I was not very clear. I was planning to have a setup with 3 states - blinking, on, and off. That is why it would be slightly better if the on/off control was a separate, in series part.

If I cannot find anything else, I will try to use the integrated flash version.
________________________


Incandescent versions will either use modern electronics, which means basically a 555 astable circuit with FET switchers to handle the higher voltages and currents, or the really old method of a bimetallic strip. I saw one of those in a Datsun 120Y once. That's a car that was produced roundabout 1970.

________________-

Yes, I was thinking the same thing - I used / changed similar ones. I wonder if this is how an incan xmas light blinks now ?
_____________________

Apparantly, the strip will heat up if current passes through it. Being bimetallic, the bits will expand at different rates, causing the strip to curl and bend away from the contact thus breaking it and allowing the strip to cool down and straighten enough to retouch the contact.

If you can find that, I'm sure you can adapt it for use with LEDs.

[/ QUOTE ]

 

[Doug Owen]

[ QUOTE ]
HarryN said:
If you can find that, I'm sure you can adapt it for use with LEDs.

[/ QUOTE ]

Maybe, but it takes a fair bit if energy to heat these rascals enough. You can fiddle with the idea, the bulbs are fairly common (yes, christmas tree bulbs work this way) as are older turn signal flashers in cars. Sometimes the work is done by a taught wire carrying the current which gets longer when hot. Bimetal strips sometimes have a crimp giving them an 'over center' action, giving hystersis and protecting the contacts. Another source is thermal switches (which is what they are), you could use the LED to heat it.

Not a very efficient way to flash a LED.

IMO, the best solution is a self flasher.

Doug Owen

 

[HarryN]

Thanks for the advice - so what kind of flashing circuit is inside of a flashing LED ? Must be some kind of small, simple, in line setup as these still only have a cathode / anode.