[sdiy] Updated Schematics of Rene/Wasp Hybrid

[René Schmitz]

Hi all,

Aaron Lanterman wrote:

> Interesting. I know they Kai Chi and Sean a 47 uF polarized since that's
> what it looks like in Rene's schematic (one side is white and the other
> black); can we guarantee correct polarity in Rene's schematic? How?

No. But Electrolytics can tolerate this. On average there is zero DC, so 
there is no negative voltage which would destroy the dielectric layer. 
For that there would need be a negative voltage on average.
(The "corrosive" chemical reactions take some time... And you have to 
overcome a certain potential before the reaction would start.)

Now this might not be good design practice, but as long as the current 
is limited nothing is going to blow up. (And there are other examples 
where people got away with it.)

> Usually R5 would go back to the - input of U1, but since the inverter
> inverts, we need to put it into the + terminal, right? (That's what I told
> them to do, but maybe I'm missing something. Let me look at R10... let's
> see... what comes out of buffer of A1 in Rene's schematic winds ups
> inverted, so if it goes into the + pin of O2 on Rene's schematic, I
> thought it should go into the - pin of U2 on the students' schematic to
> cancel the inverstion... similarly... the feedback from buffer A2 in
> Rene's schematic goes to the - terminal of the 3080, but, since the
> inverter buffer in the student schematic inverts, I had them take it to
> the + terminal.

I think the 100n caps are probably too large.
(Thats probably why the frequency maxes out at some point, the frequency 
is too low with the control current available, and the current source 
saturates since the limiting resistors are getting into effect.)

And the local feedback at U2s + input would need a 220ohms resistor to 
GND. And as Harry has said, the CMOS feedback buffer needs an input 
resistor to get a finite gain.

As for the feedback loop, I think its ok, if I'm not mistaken the sign 
is positive when you make the full circle from the node where R3 and the 
100n cap meet, back through the entire feedback arrangement.

Cheers,
  René

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