S&H

[jhaible]

> The best sample and hold is an A to D convertor & a memory,
> and then D to A.
> Will wait for say, until the eventual heat death of the universe
> with no droop. 
> My challenge to the list: how cheap can you make this?
> Perhaps with a PIC?

No PIC required.
A counter, a comparator and a DAC should do.
Start the counter when the sample pulse arrives, stop the counter when the
comparator signals that input = output.

JH.