[sdiy] Okay, I give up :-)

[Ryan Williams]

Nicolai Czempin wrote:
> Nicolai Czempin wrote:
> 
>> Okay, I'll build the 4069 circuit. I cannot hold out any longer.
>>
> Done. Of course, having used a breadboard, I wasn't able to thermally 
> couple anything. But I guess once I have it working, I can do all that 
> on one of these other boards, or even practice going through the process 
> of getting a PCB made.
> Oh, and BTW, it's not working. For some reason I bought (a) 22nF 
> capacitor(s) instead of 2.2, even though I had copied the parts list 
> from the schematics properly.
> Ah well, guess I'll have to wait until tomorrow.

Unless I'm overlooking something, using a 22nF instead should still 
work, but oscillate at much slower freqencies.. you could probably still 
glue those transistors together on the breadboard, but maybe it's a 
better experience to see what happens when they aren't thermally 
coupled. try putting your finger on one of those transistors and listen 
to the effect.

> And another BTW, it really is simple once you leave out the PWM bit. I'm 
> even beginning to understand what's happening (except for all that part 
> with the source sink; I couldn't explain why the 
> temperature-compensation works to someone else). If you leave out that 
> sink and replace the inverters by op-amps, you'll get what I'd have got 
> in my next steps with a simple 741 (more or less).

to explain the operation of the temperature compensated current sink, 
you should look on that same website, René has a good tutorial on the 
topic called " Whats that exp and tempco stuff? ". it doesn't talk about 
the same exponential source but shows why temp compensation is needed. 
you can analyze that current source in a similar way.

I had a little trouble with the PWM on my version of this circuit, it 
changed the frequency when I changed the pulse width. I modified the 
input and current sink for a higher precision version (lots more parts). 
  but this was my first experience with building from a schematic, 
modifing a schematic, and laying out a PCB. so you can see how it all 
turned out here:
http://www.sdiy.org/destrukto/modular/4069-vco.html

-ryan