Name that cap...

[Tony Duell]

> Well - the spec for the LS121 is pretty well-known.  Someone with more 

IIRC, the pulse width is something like 0.7*R*C

> caffeine and inclination than I might well look up the datasheet and 
> work out what the value ought to be.  It looks like it says "270" 
> overscribbled with "220" to me - what units I don't know.  Try 220nF. 
> If that doesn't work, try 220pF.  You'll be in the ballpark with one of 
> those.

Assuming R is within the recomended range for the IC, you are not going 
to get a 5.5us pulse (which sounds about right) with a 270nF cap. 270pF 
could well be right.

-tony