[sdiy] Oakley S&H clock LED pulse extender

[Jean-Pierre Desrochers]

Check the --> monostable example here:
http://pfnicholls.com/electronics/555_timer.html


Le 2014-06-04 14:58, Andre Majorel a écrit :
> 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 ?