[sdiy] My 4069 attempt not working

[René Schmitz]

Nicolai Czempin wrote:

> Divide and conquer, that's familiar :-)
> I did that, and it's not oscillating. So we need to look at that part.
> I did check that the gates all do their (logical, from +V to 0 and vice 
> versa) inverting business.

Is the integrator output sitting at V+? That would mean that there is no 
discharge happening. If then the output of the schmitt is also sitting 
at V+ that could mean that either the discharge diode is the wrong way 
arround, or broken, or your 4069 is fried. (Or a connection is missing.)

You can check against the latter, by takeing out the cap, and connecting 
the first gate (which is no longer an integrator) alternatingly to V+ 
and GND , and check if the logic values are alternating from gate to gate.

> However, for checking the integrator: All I see is the "clipping" 
> voltage, no ramp. I may not be looking "quickly enough", though. What 
> kind of delay should I be looking for with that 2.2nF capacitor? Perhaps 
> I should add a switch in parallel to the capacitor, so I have more 
> control over when the ramp starts ramping. I remember something about 
> frequency being proportional to 1/(RC), so to make the ramp slower (so I 
> can see it), I need to take bigger values for either, right?
> What about them diodes, can I eliminate them for the time being? All 
> they do is some kind of absolute-value computation, right? So 
> eliminating them may not give me the ramp I want, but there still should 
> be some kind of oscillation.

The diode in the integrator could be left out, but the other diode, the 
one from the schmitt trigger output to the integrator input, is 
absolutely vital. It doesn't do an absolute value computation, but 
pushes the current to discharge the cap into the integrator (when the 
schmitt is fired), and blocks a "backflow" of integrator current into 
the schmitt output. (So it can push, but not pull.)

Cheers,
  René

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