William Chops Westfield wrote:

> An LM3909 "LED Flasher" charges a cap and then discharges it in series
> with the battery to drive an LED from a single cell.  While the
> "normal" configuration uses a 300uF cap and flashes once a second,
> presumably (haven't tried it) a smaller cap would result in a faster
> rate, perhaps up to the "apparently continuously on".  Might be
> awfully dim, though - it's none too bright in the original config.

  It can be brightened by shunting the time constant resistors with a
much lower value (original is as I seem to recall, two 5k steps).  The
problem I have with it is that there is no actual "enable" pin; the
series pair of said resistors is internally connected in place so you
can decrease the fixed resistance but not increase or open it.

  Consequently, the only way to switch it on and off is to use the PIC
to feed power to it, adding the PIC I/O resistance to any other losses.

  Cheers,
        Paul B.