[sdiy] My 4069 attempt not working

[Scott Gravenhorst]

Nicolai Czempin <n.czempin at gmx.de> wrote:
>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?

It will work without the deFranco compensation (lower diode).  The one on
top is necessary.  Powered by a "high" output from the schmitt trigger, the
capacitor charges rapidly through the diode until the upper schmitt
threshold is reached.  However, once charged, it can't discharge through
that route because of the diode, so discharge is force to go through the
current sink.  The cap discharges through the sink until it hits the lower
schmitt threshold, causing another pulse which through the diode charges the
cap and ...

> 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.
>>>
>>>    
>>>
>

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