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Most novel LED flasher ?

I just built the one you referenced

formatting link
under Circuits, #23,) and it works properly with a 2N2222A.

Note that the transistor is 'backwards', ie, the emitter is connected to the

1.5k from V+. Also, I had to crank up my power supply to about 8.5v before it would start oscillating. Lower than that, it didn't oscillate.

I put the base and emitter on my scope, and it looks like the transistor is acting like a zener, holding off the current until the voltage gets to about

8.2 volts. At that point, the base starts getting more positive. When the base gets to .6V, the voltage shoots up briefly, and the emitter voltage drop to 0.

My guess as to whats happening is that the emitter-base junction is leaking charge at 8.2V, which is charging up the base. When the base-collector junction gets forward biased (base up to .6V,) current flows, causing an avalanche breakdown of some kind in the emitter-base junction. This quickly discharges the capacitor, so the current drops enough to stop the breakdown and restart the charging cycle. Its like a UJT oscillator.

Regards

Reply to
Robert Monsen
Loading thread data ...

In article , snipped-for-privacy@nowhere.com mentioned...

I think we just set a new record for lowest parts count - three parts not counting the LED. An electrolytic capacitor, a current limiting resistor, and a single standard BJT transistor, not a UJT or PUT.

I just got thru clipping together one with some alli clips. I used a BC337-25. a 470 ohm resistor, and a 330 uF capacitor. I cranked it up to 10V, but no cigar. Not even a flicker. When I got to 12V, it started to slowly flash, longer than 1 second per flash. When I got to 13V, the flash rate was much faster, somewhere in the 6 to 10 Hz range. Above that and it stopped flashing and just glowed steady. So it apparently needs a stable voltage that is very dependent on the transistor used. Also I found that if I touched the base, it does weird things like stop oscillating or speeded up. Actually the flash is more like a throb or pulse, with bright and dim phases, but no sharply defined on or off. The LED comes on bright quickly, and tapers off slowly to the dimmest point where it repeats the cycle. I guess the best way to describe it is a sawtooth wave.

Another warning: do not attempt to use the transistor for its regular purpose after using it in this circuit. Reverse biasing the E-B junction to its avalanche mode will cause the transistor's beta to be seriously degraded. If you do use a transistor for this, it's probably advisable to cut off the base lead to prevent it from being used as a regular transistor.

So there you go, two independent verifications that the circuit does indeed work, and we have set a new low in parts count. The resistor might be eliminated but at risk of excessive current. I think it should be left in. Three parts is about as low as it can get with discrete parts, even with a UJT or PUT.

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Reply to
Watson A.Name - 'Watt Sun'

Are you allowed to use an AC supply...?

-Ed

Reply to
Edward Rosten

How about 1 component: - LED in series with a flashing LED!

Reply to
Mike Harrison

Perhaps a solar panel (2V cell for RED LED), small enough power output so as not to cook the LED. The _Flash_ rate may be a bit slow, but it is flashing and only one component. (not recommended for indoor use..)

Greg the Grog

Reply to
Grog

I did it ! MwahahAHAHAHA !

LM334, 100 uF tant, 100K resistor, 2k7 resistor, white LED .

Beat that ! :)

Tried it with two regulators, both worked fine .

-A

Reply to
Andre

The parts count is a bit high but mine doesn't need a power supply :)

formatting link

Reply to
Kevin McMurtrie

Hi

How bout in addition to the LED and battery, a file? Yes, a woodworking file. Run it across the LED lead and watch the LED flash.

Or if MTTF is not an issue, just LED and small battery, connected with dry joints. Should get some flashing there, for a bit. Small battery has enough internal R to not need any resistor. Dont think we can get a lower parts count than that one. But we could improve the MTTF.

OK, motor in series with LED: some small dc motors go o/c regularly as they rotate. Thats one component and reliable.

(The avalanche tr has the same parts count as the neon flasher of course.)

Regards, NT

Reply to
N. Thornton

1 LDR 2 LEDs (one for flash, one for trigger) .

Uses the tendency of LDRs to have a delayed reaction to light .

Reply to
Andre

In article , testing snipped-for-privacy@yahoo.com mentioned...

the

about

We already have, according to the text that you included, but apparently didn't read.

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###Got a Question about ELECTRONICS?   Check HERE First:###
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My email address is whitelisted.  *All* email sent to it 
goes directly to the trash unless you add NOSPAM in the 
Subject: line with other stuff.  alondra101  hotmail.com
Don't be ripped off by the big book dealers.  Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com  You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
Reply to
Watson A.Name - 'Watt Sun'

I did . :) My circuit works with any LM334 and is fairly stable .

"Avalanche" transistor oscillators work fine at >12V - should have specified under 9V . Oops . :)

Sorry for the confusion there . BTW its quite interesting, the circuit I designed seems to work fine at 5V but behaves strangely at lower voltages . (like the LED comes on all the time) .

No doubt it would also work with a small bulb (and without that 2K7 resistor) . Gonna try that too .

-Andre

Reply to
Andre

Hmm . Might be useful as a random number generator - apply very low current to LED and use another LED or photodiode to pick up and amplify the resultant signal .

-A

Reply to
Andre

The problem is how do you tell the real signal from the dark signal of the photodiode? Then you need to work out if you need the LED at all.

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Reply to
Ian Stirling

In article , testing snipped-for-privacy@yahoo.com mentioned...

Standard convention doesn't have a space between the last letter of a sentence and the question mark, or the period [dot] for that matter. Same with the bang [!].

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@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS?   Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted.  *All* email sent to it 
goes directly to the trash unless you add NOSPAM in the 
Subject: line with other stuff.  alondra101  hotmail.com
Don't be ripped off by the big book dealers.  Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com  You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
Reply to
Watson A.Name - 'Watt Sun'

Gotcha. :)

-A

Reply to
Andre

I thought the "tried and true" method was to use a 2N3904 with its B-E junction reverse biased to generate noise? Add a 74ALS04, some Rs and Cs, mix well and turn the power on. Voila - random TTL noise :) See

formatting link
for a schematic and some info on the

3904-as-a-noise-source idea ;)

Later.

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Reply to
Philip Pemberton

letter

AFAIK standard convention dictates one question mark to denote a question so with this in mind is your question more of a question because it has three question marks?

Reply to
Mjolinor

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