[sdiy] SN76477 project / LF398 sample and hold ?'s

[Derek Holzer]

howdy,

just dropped into the list to see what's going on out there. i'm in the 
(long, drawn-out, oft-interrupted) process of building a a little 
synth-in-a-lunchbox based around an SN76477 chip, commonly used for such 
hi-brow applications as video games and pinball machines. too bad i haven't 
got it all the way up yet... anybody else work with this IC that i can ask a 
few details from?

for the list, i've got a question:
anyone have a simple schematic for a sample-and-hold circuit using an LF398 
IC? seems like the simplest way is just to have a 0/1 logic input on a 
push-button to trigger it, an output and then the hold capacitor.

then i looked at Rene Schmitz's YASH sample-and-hold circuit ( 
http://www.uni-bonn.de/~uzs159/ ) and saw a pile of gates and an extra 
transistor leading into the logic input pin. what exactly is all that for if 
all you really need to do is trigger it with a push-button switch? i'm 
curious...

also: i'll be running +5 V into it, so how big should the hold cap be?

thanks,
derek

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