[sdiy] My 4069 attempt not working

[Nicolai Czempin]

Scott Gravenhorst wrote:

>If you think there may be a problem with the current sink, you can replace
>it with a resistor to ground, a 100K pot in series with 5K for example. 
>If it doesn't oscillate like that, then something is wrong with the hookup
>of the schmitt trigger, the integrator or both.  If it does oscillate, you
>need to trouble shoot the current sink. 
>

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.

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.

> That's what I'd do.  The output
>of the integrator should be a ramp, sawtooth wave.  The output of the
>schmitt trigger should be a narrow pulse that coincides with the
>sawtooth's reset.  Your power supply arrangement sounds fine.
>
>Nicolai Czempin <n.czempin at gmx.de> wrote:
>  
>
>>Well, I got the 2.2nF Capacitor, and as some of you have guessed, it 
>>didn't make any difference to the fact that it's not working :-(
>>
>>It's kinda hard to debug when one doesn't know what to expect at 
>>different points in the circuit.
>>I tried to take some pictures with my cheap-o-the-line digicam, but the 
>>quality is so low that it's not really possible to see anything (I can 
>>basically choose between overexposed, underexposed and blurry, even at 
>>the highest resolution with the highest quality level).
>>
>>I tried to leave parts out to simplify the whole affair---only ones 
>>where I'd guess it wouldn't be a significant difference: All the stuff 
>>that's there for thermal stability is not much use when it's not 
>>oscillating at all!
>>So I eliminated the thermistors for now, and I haven't yet glued the 
>>transistors together.
>>As mentioned before, I am only using the "top half" of the 4069 IC 
>>(except for pin 7, which is connected to GND).
>>I don't have the power supply yet, so I'm using two 9V battery blocks, 
>>with GND "in the middle".
>>I have also eliminated the second input voltage, that should just have 
>>the same effect as having 0 V at the second input, shouldn't it? Or do I 
>>need to connect it to GND through the 100k resistor?
>>The V1 I'm simply connecting to +V, as I don't have any alternatives 
>>right now. But that should work too, shouldn't it? There should be 
>>*some* oscillation.
>>I did make sure that +V, -V and GND really are that, I do that every 
>>time. But I'm not sure what should happen in the different parts of the 
>>current source, and it's hard to debug that way.
>>In my childish naivety, I also tried to just leave out the current 
>>source and connect the integrator input directly to +V. Still no 
>>oscillation.
>>I'm pretty sure that I've made the correct connections (no diodes the 
>>wrong way round or anything like that). I can still post a picture if 
>>that would help anyone, but as I said they are all very low quality.
>>
>>Can someone help please? "Just" a walkthrough as to what I should see on 
>>the scope at certain key points would be very helpful.
>>
>>Sigh. I really would like to get this to work, otherwise I'll have to 
>>get back to crummy 741 stuff.
>>
>>    
>>