"Dave Liquorice"
Er but the 3909 has been obsolete for at least 3 years, you can still get them though. $14 plus postage. You could buy a new Fng alarm for that. !
"Dave Liquorice"
Er but the 3909 has been obsolete for at least 3 years, you can still get them though. $14 plus postage. You could buy a new Fng alarm for that. !
I have a load of LM3909s. In fact a chip just fell to the floor from a "bookshelf" in the living room - it was a 3909 :-)
Frank Erskine
Good for you, now for a little gold star, tell me were you can still buy them in the UK and at what price.
Standard building block bistable circuit will do what you want. Two transistors, two capacitors and four? resistors.
Hoew about a unijunction with the LED in its collector?
It would be hard (maybe impossible) to get the on-off ratio
50%. Also, the with the output being saw-tooth rather than square wave in a conventional unijunction oscillator, the LED would fade off each time. BTW, there's no 'collector' in a unijunction transistor -- I presume you mean the drain? (I think it's about 30 years since I last used a UJT, and that was to generate a timebase for an oscilloscope I was building from an old telly;-)
I've just come across this which appears to do what you want, although the flash rate might be a bit quick?
And that was probably 5-10 years after they stopped making them :-)
Oh have they? How sad. ...and I still remember the part number I used - 2N2646
A quick search on this number reveals two companies still make them - Comset and BOCA. Never heard of either but at $2 a piece there's obviously enough profit in it for some garage semicon plant to churn them out :-)
Ah, the metal TO-18 version. How many would you like? RS still stock them and they are sold individually :)
G.
snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel)
Just to be pedantic its E,B1,B2 on a UJT,Its an electronic switch, no gain so no collector or drain :-) It would work, but to be effective would need anther transistor, which would make the component count as high as an ordinary flip/flop.
I thought that a very short pulse every few seconds was what was required.
Don't use teh gate, use the (drain? No that's a FET surely...)
I thought that the anode went into heavy conduction durng the pulse discharge phase.
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