[sdiy] 566

[Scott Gravenhorst]

See the Thomas Henry 8038 design that I posted earlier.  Not
expo, but converter could be added.  I think you are asking for
quite a bit to get sine and still low parts count.  I'm not
absolutely certain, but I think you won't find other 2 chip
designs that have 3 output waveforms.  According to Mr. Henry,
the VCO stays in tune (is linear), contrary to most opinions
about the 8038, but his CV approach is different putting the
current source in the feedback loop of an opamp.  The 8038 has
square/tri/sine outputs, but as Mr. Henry states, these outputs
must be level shifted and amplitude adjusted to make them all
the same.  He does this with 2 ICs, one 8038 and one quad
opamp.  The 8038 is cheap as dirt.

Also, you've now added sine wave as part of the design, this
cannot be done with a 566 without more components.

As far as cheap and linear VCOs go, I think the René Schmitz
4069 is very good, but it's a saw VCO (with PWM).

jbv <jbv.silences at club-internet.fr> wrote:
>
>
>Steve Ridley :
>
>> 'evening all...
>>
>> Maybe I'm being a bit dim tonight, but I just can't see why
>> anyone gets excited about these ICs.   They're scarce, can
>> be expensive and need some clever cludging make a VCO
>> which still goes flat above 9KHz.  With people making so
>> much effort to get them and build VCOs out of them, I feel
>> I must be missing something, but I can't see what?
>
>OK I see your point. But when you get 40 pcs for less than
>$30 you start to wonder what to do with these...
>
>Anyway, let's put it the other way around : what could be the
>best (and cheapest, in terms of parts # and PCB room) solution
>for a bank of VCOs (and possibly VCFs & VCAs), providing
>that :
>- tuning between VCOs is crucial
>- all expo converter operation for CV inputs can be handled by
>uC / software
>- ouputs should include at least square / tri / sine...
>
>Thanks,
>JB
>

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