[?] Audio VCO design

Started by David Chapman November 20, 2009
   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 Chapman" <dave@minda.co.uk> wrote in message 
news:DDdWWuJ6OmBLFw+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
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
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
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
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
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.
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 | | | Voice:(480)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
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.
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
On Fri, 20 Nov 2009 14:14:56 -0800, whit3rd wrote:

> 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.
In other words, a 555. ;-)
> Analog switches, diode switches, current mirrors, or transconductance > amplifiers are the key components.
Cheers! Rich
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
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) --------------------------------------------------------------------------
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
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 | | | Voice:(480)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
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
   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) --------------------------------------------------------------------------
<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
"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
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