[sdiy] My 4069 attempt not working

[Scott Gravenhorst]

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.  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.
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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