[sdiy] Oakley S&H clock LED pulse extender

[Paul Anderson]

Can you draw up the schematic? The ASCII art isn't working out. 

Sent from my iPhone

> On Jun 4, 2014, at 2:58 PM, Andre Majorel <aym-htnys at teaser.fr> wrote:
> 
> I'm driving an Oakley S&H with a very short pulse (about 23 µs).
> To make the flashing of the LED more visible, I've tried adding
> a capacitor.
> 
>                +15 V
>                  |
>                A +----------+
>                 _|_         |
>                 _V_  LED    |
>                  |          |
>                  |          |
>                  >          = Ca
>                  <  R2      |
>                  >  1.8 k   |
>                  <          |
>                  |          |
>                B +----------+
>                  |          |
>                |/  Q1       |
>            ----|   BC549    = Cb
>                |\  NPN      |
>                  |          |
>                C +----------+
>                 _|_
> 
> A 100 nF at Ca or Cb doesn't seem to do much. With a 2.2 µF at
> Ca or Cb, the short pulses don't even light up the LED.
> 
> I was hoping that Q1 could supply enough current to "instantly"
> load a capacitor large enough to keep the LED on for a tenth of
> a second or so.
> 
> What am I doing wrong ?
> 
> -- 
> André Majorel http://www.teaser.fr/~amajorel/
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