[sdiy] 4053 triple SPDT for VCO

[René Schmitz]

Hi Aaron, Chad and all,

> Really? Harry's post got me worried...

Really. I had a 4053 with this configuration on the breadboard not too 
long ago. The switching was straight to the rails between 0 and 15V. I 
was worried about shorting too, but the circuit didn't care about that, 
and worked. :-)

(I was testing if I could use a switch without an extra comparator as a 
schmitt-trigger, which would have been handy, since one could use the 
other switches for discharge, turned out the switching threshold does 
drift too much for that, but here the 319 should remedy that.)

I have been haunted by the make break behaviour and the intermediate 
switching to GND also. Yes, Harry is absolutely right, and a little 
caution is in order, you will get unexpected effects if you use CMOS 
switches "naively". (Actually that goes for almost every other component 
as well.) Sometimes you get away by changeing the circuit somewhat, and 
knowing what really goes on inside the ICs and discretes does help you 
then. (IMO the biggest mistake is to see them as "black boxes", they are 
not.)

This configuration was not meant as a cooking recipe anyway, I expect to 
  see alterations of it, because I haven't tested it.
Also I didn't say you have to use the supplies, but that it will work, 
somewhere below that will of course also work. (Might be better, might 
be worse.)

Btw. if these auxiliary supplies are current limited (opamps can supply 
~20mA, a pseudo zehner bandgap will have a limit because of the pullup 
resistor, and so on, so this is very likely that you have this 
unconsciously done already), then this should put worries about shorting 
current aside.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159