[?] Audio VCO design

[David Chapman]

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@minda.co.uk)
--------------------------------------------------------------------------

 

[Holloway,Graham (UK)]

"David Chapman" <dave@minda.co.uk> wrote in message
newsDdWWuJ6OmBLFw+u@chassis.demon.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.
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@minda.co.uk)
--------------------------------------------------------------------------

David

Don't use the 4046, unles you are prepared to calibrate each one. I found
3:1 variations between parts from different suppliers, i.e. frequency vs.
volts.

regards
Graham H

 

[John Fields]

On Fri, 20 Nov 2009 09:39:06 +0000, David Chapman <dave@minda.co.uk>
wrote:

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

---
View in courier:
.. VCC
.. |
.. +-----------|---------+
.. | |8 |
.. [Rt] +----+----+ |
..VC>--------+ | |_ Vcc | |
.. | +---7-O|D VC| |
.. [LED]--> [LDR] | _| |
.. | +----6-|TH R|O-4-+
.. | | |__ |
.. | +---2-O|TR OUT|-3----->OUT
.. [R] | | GND |
.. | [Ct] +----+----+
.. | | 7555 |1
..GND>-------+---------+-----------+

or:


.. +--------[Ct]--------+
.. | |
.. | | \ HC04 | \ |
..Vc>---[R]--+ +---| >O--+--O| >--+-->OUT
.. | | | / | | /
.. [LED]---> [LDR] |
.. | | |
..GND>-------+ +---[R]----+


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


http://www.google.com/search?q=Vactrol&btnG=Search&hl=en&rlz=1T4GFRC_en&sa=2

JF

 

[Phil Hobbs]

David Chapman wrote:

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

The old metal gate 4046 has a much wider VCO range than the HC version,
which craps out at low control voltages, so that's good. The frequency
tolerance is around +-50%, however, so you might wind up with 75 Hz to 6
kHz or 25 Hz to 2 kHz, which might matter to you.

I'd either nudge the frequency specs up a bit to accommodate that
tolerance, or if I wanted something more accurate, use a BJT diff pair
to provide a charging current to a cap and a little comparator with
well-defined hysteresis to reset it. That way you get a nearly
exponential tuning curve, which is a good match to human hearing, and a
much more dependable frequency range. If you're feeling posh, you could
use an LM13700 and a few Rs and Cs for the whole job.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Fri, 20 Nov 2009 09:39:06 +0000, David Chapman <dave@minda.co.uk>
wrote:

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

http://www.analog.com/en/analog-to-digital-converters/voltage-to-frequency-converters/products/index.html

http://focus.ti.com/lit/ds/sbvs023/sbvs023.pdf

If you want a nicer sound than a square wave, you can generate a
multiple of the desired frequency and run it through some sort of
simple sine shaper.

John

 

[Rich Grise]

On Fri, 20 Nov 2009 09:39:06 +0000, David Chapman wrote:

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.

I'll probably get pilloried for this, but it sounds like the app cries

out for a 555 or 7555.

You might have to scale the tuning voltage a bit.

Good Luck!
Rich

 

[Jim Thompson]

On Fri, 20 Nov 2009 09:39:06 +0000, David Chapman <dave@minda.co.uk>
wrote:

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

That 80:1 tuning range is pretty nasty. Do you need that in one swell
foop, or can you use some form of ranging.?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I once said, "We will bury you," and I got into trouble with it.
Of course we will not bury you with a shovel.
Your own working class will bury you. - Nikita Khrushchev

 

[Joerg]

David Chapman wrote:

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.

The LM331 can do that, is nicely linear but you'd have to add the proper
control voltage offset so you get the range you want:

http://www.national.com/ds/LM/LM231.pdf

However, check whether supply voltage and power consumption fit your
requirements. Also, only available in DIP package.

A really slick and precise solution is a micro controller with AD
converter in there. The MSP430F2003 would be a good candidate and for
the basic function you'd need almost no external parts other than a
decoupling capacitor. Feed you control voltage to its built-in AD
converter, digitally offset and scale its output to whatever you need
and let the output set the overflow register of the internal timer. The
timer output gets piped to a port pin and, voila, there is your output
frequency. Even without any external crystal and just using the internal
digitally controlled oscillator (DCO) the precision would be in the
single digit percent. TI has super-cheap development kits for that series.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Spehro Pefhany]

On Fri, 20 Nov 2009 09:39:06 +0000, the renowned David Chapman
<dave@minda.co.uk> wrote:

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

If you don't mind a linear 50mV-4V for 50Hz-4kHz, it's pretty easy to
do this with a couple of opamps (or an op-amp and a comparator) and a
transistor (BJT, MOSFET or analog switch). You set one amplifier up as
a +/- integrator, output goes to a comparator with hysteresis which
controls the +/- switching. You get a triangle wave and a square wave
output.



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[whit3rd]

On Nov 20, 1:39 am, David Chapman <d...@minda.co.uk> wrote:

   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.

   I'm considering using the CMOS 4046 PLL IC,

The thresholds in a '4046 (CMOS) are variable unit-to-unit, some
better precision can be had with a linear design; I'm thinking
of XR2206, LM331, and similar chips. The basic scheme is to
use the voltage input to program tracking current source + sink
elements, onto an integrator-connected amplifier into a
comparator with suitable hysteresis. Analog switches, diode
switches, current mirrors, or transconductance amplifiers are
the key components.

 

[Jan Panteltje]

On a sunny day (Fri, 20 Nov 2009 18:13:51 -0500) it happened Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote in
<df8eg5d5i3reaet7sjh6b5jgbh75h7ac3e@4ax.com>:

On Fri, 20 Nov 2009 09:39:06 +0000, the renowned David Chapman
dave@minda.co.uk> wrote:


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

If you don't mind a linear 50mV-4V for 50Hz-4kHz, it's pretty easy to
do this with a couple of opamps (or an op-amp and a comparator) and a
transistor (BJT, MOSFET or analog switch). You set one amplifier up as
a +/- integrator, output goes to a comparator with hysteresis which
controls the +/- switching. You get a triangle wave and a square wave
output.



Best regards,
Spehro Pefhany

OK, my turn...
X MHz xtal, X + a bit MHz VCO (varicap), dual gate MOSFET mixer, lowpass.
Can make a very wide range.
But I would use the 4046 too.

 

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

 

[Phil Allison]

"John Fields"
David Chapman <dave@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

 

[Tim Williams]

<osr@uakron.edu> wrote in message
news:4f6187b4-4ad2-42a9-be9a-300c9dd725b4@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

 

[David Chapman]

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@chassis.demon.co.uk>, David Chapman
<dave@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@minda.co.uk)
--------------------------------------------------------------------------

 

[John Fields]

On Sat, 21 Nov 2009 13:42:37 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"John Fields"
David Chapman <dave@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

 

[Jim Thompson]

On Sat, 21 Nov 2009 10:31:27 +0000, David Chapman <dave@minda.co.uk>
wrote:

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
[snip]

Just read my patent about linearized control....

3,665,343 Voltage Controlled Multivibrator

(In PDF form on my website)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

"The source of well-being in this country is employment."

- Steve Wynn, on Fox News Sunday, 11 October 2009

 

[Frank Buss]

David Chapman wrote:

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 would use a microcontroller, as Joerg suggested, because then you'll need
just one chip and one capacitor and you're done. I've tried it with a PIC:

http://www.frank-buss.de/vco/

The lite edition of the HI-TECH C compiler has even floating point support,
so it is very easy to implement it. You can get the PIC for less than $ 1
for 10 parts:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PIC12F675-I/SN-ND

Works from 2V to 5V. And you'll need a programmer. I have this one:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PG164120-ND

Don't use the PICkit3, until they have fixed the firmware

The MPLAB IDE and the compilers (the non-optimizing versions, which works
good for most projects) are free.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de

 

[David Chapman]

In article <cwhtkdo9z24b$.wqaa2raqk59g$.dlg@40tude.net>, Frank Buss
<fb@frank-buss.de> writes

David Chapman wrote:

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 would use a microcontroller, as Joerg suggested, because then you'll need
just one chip and one capacitor and you're done. I've tried it with a PIC:

What an elegant solution! Many thanks Frank.

Your proposed way of solving the problem really highlights the
difference between my ancient way of thinking which usually involves
discrete components and some digital or analogue ICs, and the modern
'micro fits all' approach.

I do feel old :-( ....but then I am, so many thanks for bringing
me up to date. I'll certainly give the PIC approach a go now.

Thanks again - Dave

--
David C.Chapman - (dcchapman@minda.co.uk)
--------------------------------------------------------------------------

 

[Frank Buss]

David Chapman wrote:

What an elegant solution! Many thanks Frank.

My pleasure!

Your proposed way of solving the problem really highlights the
difference between my ancient way of thinking which usually involves
discrete components and some digital or analogue ICs, and the modern
'micro fits all' approach.

I do feel old :-( ....but then I am, so many thanks for bringing
me up to date. I'll certainly give the PIC approach a go now.

It is never too late to learn new things, e.g. I'm 36 and trying to learn
piano playing

http://www.youtube.com/watch?v=RC9pS9lOrNw

BTW: the PIC is not the best solution if you want high precision, because
of the missing capture compare timer, which would be possible with some AVR
microcontrollers or better PICs. The best would be a hardware PWM module,
which are integrated in bigger microcontrollers, but you wrote that it is
not important, so my very simple solution might work for you.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de