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From: osr on 20 Nov 2009 21:21
The curse of a quasi photographic memory, I can remember nearly every
web page I've ever been to via context clues:

Here is a recent memory of where a vco was using a few transistors.
I'm sure Its only good at room temp, but the price is right:

http://www.4qdtec.com/mvbz/vco2.gif
From: Phil Allison on 20 Nov 2009 21:42

"John Fields"
David Chapman <dave(a)minda.co.uk>

>
>> As part of a larger system, I need to design and build an audio VCO
>>which will produce tones ranging from around 50Hz to 4KHz or so when the
>>applied DC input voltage changes from 0.5volts to 2.5volts.

( snip ASCII art monstrosity )


> The LED/LDR combo or an incandescent/LDR combo is available as a single
> device called a "Vactrol":

** The OP is in the UK.

Very likely, the RoHS directive will prohibit the use of a Vactrol.

Cos the LDRs ( ie CdS cells) inside are made with evil and forbidden
Cadmium.

Various folk have been trying to get the insane bureaucrats in Brussels to
grant a general exemption for CdS cells on the grounds there is no similar
replacement device available - but with no success.

BTW

I know about the one Marshall Amplification got for professional audio, but
it expires in a few weeks.


.... Phil



From: Tim Williams on 21 Nov 2009 03:40
<osr(a)uakron.edu> wrote in message
news:4f6187b4-4ad2-42a9-be9a-300c9dd725b4(a)r31g2000vbi.googlegroups.com...
> The curse of a quasi photographic memory, I can remember nearly every
> web page I've ever been to via context clues:
>
> Here is a recent memory of where a vco was using a few transistors.
> I'm sure Its only good at room temp, but the price is right:
>
> http://www.4qdtec.com/mvbz/vco2.gif

I liked this thing,
http://webpages.charter.net/dawill/tmoranwms/Circuits_2008/Triangle.gif
of course it can be simplified a bit if you don't need it to be as fancy.
And if you're not running up to 40MHz, you can ease off on the bias current,
too. ;-)

The nice thing about this circuit is its wire range. 50Hz to 4kHz is a very
small part of the total range.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


From: David Chapman on 21 Nov 2009 05:31

Many thanks to all those who have taken the time to contribute to
this thread.

I'm overwhelmed by the number of different and interesting suggestions
that have been offered. As I said in my original posting, I'm not
looking for an ultra-linear or accurately repeatable solution so the
simpler the better for this application. The cross-coupled
multivibrator arrangement looks very simple and effective so I'll
probably be trying that to start with and then checking out the other
design suggestions.

Thanks once again for all of your suggestions. MUCH appreciated.

- Dave

.

In article <DDdWWuJ6OmBLFw+u(a)chassis.demon.co.uk>, David Chapman
<dave(a)minda.co.uk> writes
>
> As part of a larger system, I need to design and build an audio VCO
>which will produce tones ranging from around 50Hz to 4KHz or so when
>the applied DC input voltage changes from 0.5volts to 2.5volts.
> This will be used simply as a tuning aid for visually impaired users so
>the actual voltage/frequency relationship, and waveform produced, is not
>at all critical. Supply voltage of the VCO can be in the range 3.3v - 5v DC.
>
> I'm considering using the CMOS 4046 PLL IC, but wonder if anyone in
>this NG has any better suggestions to offer. FWIW, price is not the most
>important consideration.
>
> Any suggestions will be much appreciated.
>
> TIA - Dave
>

--
David C.Chapman - (dcchapman(a)minda.co.uk)
--------------------------------------------------------------------------
From: John Fields on 21 Nov 2009 07:36
On Sat, 21 Nov 2009 13:42:37 +1100, "Phil Allison" <phil_a(a)tpg.com.au>
wrote:

>
>"John Fields"
> David Chapman <dave(a)minda.co.uk>
>
>>
>>> As part of a larger system, I need to design and build an audio VCO
>>>which will produce tones ranging from around 50Hz to 4KHz or so when the
>>>applied DC input voltage changes from 0.5volts to 2.5volts.
>
>( snip ASCII art monstrosity )
>
>
>> The LED/LDR combo or an incandescent/LDR combo is available as a single
>> device called a "Vactrol":
>
>** The OP is in the UK.
>
>Very likely, the RoHS directive will prohibit the use of a Vactrol.
>
>Cos the LDRs ( ie CdS cells) inside are made with evil and forbidden
>Cadmium.

---
This would work, then:

http://www.fairchildsemi.com/ds/H1%2FH11F1M.pdf
---

>Various folk have been trying to get the insane bureaucrats in Brussels to
>grant a general exemption for CdS cells on the grounds there is no similar
>replacement device available - but with no success.

---
Figures...

Idiotic sons of bitches would bite off their nose to spite their face.
---


>BTW
>
>I know about the one Marshall Amplification got for professional audio, but
>it expires in a few weeks.

---
Pity.

Just another example of europe trying to control the world, huh?

JF
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