Hi Russell,

On Thu, Aug 04, 2005 at 12:58:53PM +1200, Russell McMahon wrote:
>
> The attached circuit, which I "invented" based on a vvv old flasher 
> cct, may be useful depending on how you want to use it. All I did was 
> add the L - I assume many others have dome the same. It works but can 
> be finnicky. There's more to getting it right than meets the eye. As 
> shown it has minimum component count but an extra R or two can help.
> 
> I posted this about 2.5 years ago so there will be discussion in the 
> archives back then.
> 
> LED2 load position adds Vbattery to Vflyback but may not fully 
> visually extinguish the LED during off times depending on LEd 
> characteristics.
> 
> LED1 position uses only flyback energy. You may need to invert your 
> brain to understand how it lights with the polarity shown :-). (People 
> who already have inverted brains will have no problem).
> 
> Play with components. Add extra components as desired. eg a resistor 
> in series with cap will alter discharge time.
> R2 must be high enough that base current x Bet1 x Beta2 will not hold 
> load on at end of flash cycle.
> Q1b-Q2c needs a resistor if Vbat > 1 cell and may benefit even with 1 
> cell.

Thanks for the circuit. It seems perfect for breadboarding and experimenting
with! In my previous message I discounted the idea of using a PIC, a 12F629
for instance, as a replacement but the responses made me think that it might
just work and use less current to boot. Such a circuit would require more
components than a LM3909 circuit would, but still a very interesting idea.

Thanks for all the good replies everyone.

Matthew

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