Unijunction transistor LED flasher

Is the LED on between flashes?

What kind of dumb question is that? Of course it is... but at a far lesser current... determined by the inter-base resistance. ...Jim Thompson

You can view it at the youtube link ?_?

On a sunny day (Fri, 25 Oct 2013 12:50:00 -0700) it happened John Larkin wrote in :

The LED is slightly on between flashes, in the comment section on youtube I mention that a resistor parallel to the LED should fix that.

Actually it could be a nice feature for a flash, to have some light in-between flashes.

Nothing like spec'ing out an obsolete hard-to-get and expensive part that runs $5-$10 per copy, maybe less if you buy 10x more than you need, when 555s are available for the same job at under $0.15.

On a sunny day (Sat, 26 Oct 2013 06:42:08 -0700 (PDT)) it happened snipped-for-privacy@gmail.com wrote in :

You payed too much. It is nostalgia, and you should know this stuff, basic semiconductor stuff.

Do you get free linefeeds with the 15 cent part?

Personally I would use a PIC 12F628 or similar. I did build a small one with a LED that could send light signals. No external parts except perhaps for a decoupling cap, use a 3.7 V liion.

I think the old story is to have it send the IR 'off' signal for as many teevee makes as you can get data for, and use a power IR led, and walk down the street, seeing teevee after teevee go out.

Would it work with double glazing?

Mitch, the guy who runs Cornfield, is also the founder of Noisebridge.

Generally, yes. See e.g.

Cheers

Phil Hobbs

On a sunny day (Sat, 26 Oct 2013 08:13:54 -0700) it happened John Larkin wrote in :

Yes, that is it.

Very big site,

Does that mean that we need to know how to do it with neon bulbs, too? And maybe with relays?

Actually, a neon bulb flasher is better, because your amplifying element is your light emitting element.

On a sunny day (Sat, 26 Oct 2013 12:26:19 -0500) it happened Tim Wescott wrote in :

Oh YES!

Na, short lifetime, low light level, high voltage needed.

I once made one with a stoboscope U bulb.

You can make those as powerful as you want..

The best flashes are still nukes though.

f.

You might get a clue that the UJT and its application circuits look a LOT l ike the prototype of the 555 architecture. There's just no comparison betwe en performance, you're not locked into storing a lot of capacitor charge on a big component to be dumped into the LED and you have much more precision and flexibility with duty cycle and frequency.

And most all applications that once used a UJT are now implemented using a PUT (Programmable Unijunction Transistor).

The UJT was never a very predictably performing device. ...Jim Thompson

I guess that is why they were not used in millions of products.

Even they seem to be on the way out.. I don't see the 2N6028 widely available in SMT, which is a bad sign for future availability (not many new design-ins).

Best regards, Spehro Pefhany

Used properly, UJTs were fine. We used them in all sorts of timing circuits, like cosine-modified ramp triac triggers and stuff. I can't recall having problems.

Jan didn't include a resistor from V+ to B2. I think that increases the regeneration, and limits peak current. That's also the place to get negative pulses, like to drive a PNP.

I'd almost forgotten about UJTs.

I had a cute one-shot circuit I used to use, made from a TTL flipflop and a PUT.

Of course, because threshold is that eta parameter x VB2-B1, so that voltage drop across the B2 resistor adds to the regeneration.

Larkin is just bloviating. He's, as always, just a wee bit clueless, but relishes his name in print irrespective of his nonsensical spew

...Jim Thompson