Yeah, I still have a few LM3909's blinking LED's scattered about the house.
There is something highly 'kewl' about an LED that flashes (very brightly)
for 5 years on one D-cell. I wish they still made these IC's

Peter Moreton

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of M. Adam Davis
> Sent: 02 June 2004 04:12
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [pic]: PIC vs. 555
>
>
> Under 50% requires a diode:
> http://www.williamson-labs.com/555-circuits.htm
>
> What I want is a replacement for the venerable lm3909.  I suppose one
> could modify the joule thief for this with an extra cap,
> perhaps a zener...
>
> -Adam
>
> Mike Hord wrote:
>
> > Not to mention the PITA that getting a 50% duty cycle at the exact
> > frequency you want, or getting a duty cycle above 50% (right?  Over
> > 50% requires a diode, right?).
> >
> > So let's add the parts count up:
> >
> > PIC Based- 1 PIC, 1 decoupling cap.
> > 555- at worst, 1 diode, two caps, three resistors, 555.  At best,
> >             555, two caps, two resistors.
> >
> > Of course, the PIC has to be programmed, can only drive up to 25 mA,
> > and is limited to integer multiple of 1 uS, and can only
> run up to a bit
> > more than 5 volts.  OTOH, you could do multiple frequencies with one
> > chip, or at least have the complement available.
> >
> > All in all, no, a PIC is not ALWAYS a replacement for a
> 555, but it can
> > be a great replacement for it in the right situation.
> >
> > Mike H.
> >
>
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