Audio VCO design
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From: Holloway,Graham (UK) on 20 Nov 2009 06:34 "David Chapman" <dave(a)minda.co.uk> wrote in message news:DDdWWuJ6OmBLFw+u(a)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(a)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
From: John Fields on 20 Nov 2009 09:11 On Fri, 20 Nov 2009 09:39:06 +0000, David Chapman <dave(a)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
From: Phil Hobbs on 20 Nov 2009 09:13 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
From: John Larkin on 20 Nov 2009 11:38 On Fri, 20 Nov 2009 09:39:06 +0000, David Chapman <dave(a)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
From: Rich Grise on 20 Nov 2009 16:25
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 |