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'[EE]: Sine wave generation from simple components.'
2002\02\20@024448 by Nick Veys

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I've seen generating sine waves using PICs and other associated
"complex" hardware in the archives.  And can find a /couple/ web sites
showing some oscillator and integrating amp sine generators but none
seem too complete or tested.

I'm curious how I could go about generating a (roughly) 0-5 Vpp sine
wave, in the range of 1Hz or less...  It doesn't have to be very
accurate, just simple, and generate a periodic wave.

I'm looking for something made from (fairly) basic components (op amps
probably being the most complex), no 555 timers, etc, that's cheating!

My engineering schooling is limited on the EE side (more digital) so I
can't seem to come up with something that works! :)

Thanks!

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2002\02\20@025509 by Vasile Surducan

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Hi Nick, good to hear you again,
Maybe the best cheaper and stable 1Hz, pure sinusoidal generator is the
wien bridge fet stabilised oscillator.
This means: one operational amplifier, one simetrical rc network, one
diode and one fet ( also some extra resistors )

best, Vasile

On Wed, 20 Feb 2002, Nick Veys wrote:

{Quote hidden}

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2002\02\20@030215 by Jinx

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You can do it with an R-2R ladder. At 1Hz the sine wave
will be a little chunky, but you could smooth it by using an
op-amp that has its slew rate slowed down with a capacitor
in the feedback path.

If you aren't terribly fussy, a 4-bit R-2R DAC would give
fairly reasonable results with just an RC filter on the output
rather than the op-amp idea. It's only 1Hz after all

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2002\02\20@032046 by Nick Veys

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> Hi Nick, good to hear you again,
> Maybe the best cheaper and stable 1Hz, pure sinusoidal
> generator is the wien bridge fet stabilised oscillator. This
> means: one operational amplifier, one simetrical rc network,
> one diode and one fet ( also some extra resistors )
>
> best, Vasile

Ok, I have seen those around.  I have seen several with a lamp in the
circuit which I found quite odd, but just ran across one w/o.  I'll have to
play around with them, though I can't find any with FETs.

{Quote hidden}

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2002\02\20@032659 by Jinx

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> wien bridge fet stabilised oscillator.
> This means: one operational amplifier, one simetrical rc
> network, one diode and one fet ( also some extra resistors )

How about the WBO design with an NTC thermistor
as the feedback resistor ?

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2002\02\20@034725 by Vasile Surducan

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On Wed, 20 Feb 2002, Jinx wrote:

> > wien bridge fet stabilised oscillator.
> > This means: one operational amplifier, one simetrical rc
> > network, one diode and one fet ( also some extra resistors )
>
> How about the WBO design with an NTC thermistor
> as the feedback resistor ?
>
 It works, but with lazy stabilisation. It works also with 5mA bulbs
with the same problem. However if less than 1Hz is required could be
a good way to do it.

btw, Jo, is not the middle of the night or early in the morning in NZ ?

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2002\02\20@040658 by Jinx

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> btw, Jo, is not the middle of the night or early in the
> morning in NZ ?

Dunno, haven't looked outside lately

10:05pm actually. Just spent 15 minutes rummaging around
in Philips new data sheet site

http://www.philipslogic.com/datasheets/

I've got an oscillator circuit that I used for a guitar tremolo. It
took some playing around with to get it very slow, I'll dig it
out later. It used a couple 0.47uF capacitors and a 741 which
drives an MC3340 voltage controlled amp. The problem I found
with those low frequency ones using op amps and capacitors
is that the sine wave wasn't always very symmetrical. Even a
chip like the 8038 has a lumpy sine wave at LF

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2002\02\20@045756 by Vasile Surducan

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On Wed, 20 Feb 2002, Jinx wrote:

> > btw, Jo, is not the middle of the night or early in the
> > morning in NZ ?
>
> Dunno, haven't looked outside lately
>
> 10:05pm actually. Just spent 15 minutes rummaging around
> in Philips new data sheet site
>
> http://www.philipslogic.com/datasheets/
>
> I've got an oscillator circuit that I used for a guitar tremolo. It
> took some playing around with to get it very slow, I'll dig it
> out later. It used a couple 0.47uF capacitors and a 741 which
> drives an MC3340 voltage controlled amp. The problem I found
> with those low frequency ones using op amps and capacitors
> is that the sine wave wasn't always very symmetrical. Even a
> chip like the 8038 has a lumpy sine wave at LF

 maybe there are two distinct problem:
1. the offset of the OA is not compensated
2. the output is AC coupled through a capacitor and there is no
resistive load to ground behind this capacitor. The effect is a variable
DC component passing by through the capacitor untill full charge.

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2002\02\20@074301 by Jinx

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>   maybe there are two distinct problem:
> 1. the offset of the OA is not compensated
> 2. the output is AC coupled through a capacitor and there is no
> resistive load to ground behind this capacitor. The effect is a
> variable DC component passing by through the capacitor untill
> full charge.

http://home.clear.net.nz/pages/joecolquitt/tremolo.html

The circuit is in the bottom left. Quite happy with it as a
LFO for a tremolo unit. A good smooth volume control
with the MC3340 VCA

Top left is a very old guitar tremolo as you can tell by the
germanium transistors. Classic oscillator that works just
as well with newer npn, but square wave output though

Top right is an old one that uses a light bulb. OK, but
chews through the power and works by brute force - shorts
the input to ground through the pot

Bottom right is the Wein bridge using an RA53, which had
got expensive the last time I looked

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2002\02\20@084737 by Edson Brusque

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Hello Jinx,

> Bottom right is the Wein bridge using an RA53, which had
> got expensive the last time I looked

   sorry for my ignorance but what's an RA53? Yes, I've searched but found
no information. :)

   Regards,

   Brusque

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2002\02\20@092719 by Raymond Liu

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How about do it in digital way? An osillator, a ripple counter, an EPROM, a
R-2R network, and optionally a low-pass filter. Osillator can be as simple
as a cap and a resistor plus a schimitte trigger. Ripple counter can be
CD4040. Save the pre-calculated sine waveform in EPROM and use the counter
to read this waveform out. This may not be as simple as you expect but can
produce fairly stable sine signal.

-Raymond

{Original Message removed}

2002\02\20@093352 by Alan B. Pearce

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>sorry for my ignorance but what's an RA53? Yes, I've searched but found
>no information. :)

STC (the British telecomms company) used to make a family of thermistors, of
which the RA53 was one often used in audio oscillators. The family were tiny
thermistor beads about 1mm dia mounted in a glass envelope about 20mm long
and about 10mm dia. I think the glass envelope was evacuated to minimise the
thermal time constant.

The RA53 was very nice in that its characteristics meant the oscillator had
a 1V rms output level when used in a wein bridge oscillator, without any
set-up problems. Very common device for this use back in the 60's.

I had another thermistor of the same family which gave a different output
voltage, and try as I might I could not change the voltage without a lot of
effort. These devices had a very wide operating range.

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2002\02\20@111558 by Martin Peach

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For very low frequencies (I have used it for envelope generation) you can
encode the duration of each step rather than the value at each sample. This
gives much better data compression and low distortion. Thus you can use the
EPROM to store the time between LSBs rather than the full sample value for
each sample time, which results in megabytes of 0000s followed by terabytes
of 0001s and petabytes of 0010s... lots of repetition. I would think a
PIC12C509 fitted with an r2r ladder feeding an opamp-based lowpass filter
would make an excellent 5-bit DAC for low frequencies. The sixth bit would
be a serial control input.
/\/\/\/*=Martin

----- Original Message -----
From: "Raymond Liu" <EraseMERLiuspamspamspamBeGoneapplanix.com>
To: <RemoveMEPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Wednesday, February 20, 2002 9:23 AM
Subject: Re: [EE]: Sine wave generation from simple components.


> How about do it in digital way? An osillator, a ripple counter, an EPROM,
a
> R-2R network, and optionally a low-pass filter. Osillator can be as simple
> as a cap and a resistor plus a schimitte trigger. Ripple counter can be
> CD4040. Save the pre-calculated sine waveform in EPROM and use the counter
> to read this waveform out. This may not be as simple as you expect but can
> produce fairly stable sine signal.
>
> -Raymond
>
> {Original Message removed}

2002\02\20@144550 by Jinx

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> sorry for my ignorance but what's an RA53? Yes, I've
> searched but found no information. :)

As Alan says, RA53 very popular thermistor for audio oscillators.
I've had an oscillator made from a circuit in the Maplin catalogue
of around 1978. Worked very well, except, oh dear, I broke the
RA53. I have another oscillator now and wouldn't pay the $40
for a new RA53 or even probably bother shopping around

You can see an RA53 here, at Radio Spares site

www.rshttp://www.co.nz/

Enter 151114 as the product code in the Search And Find option

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2002\02\20@162622 by Harold M Hallikainen

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       Well, you could go with a Wein Bridge oscillator. It consists of a
non-inverting amplifier with a gain of three (generally made with an op
amp and a couple resistors), a series RC from the output to the input,
and a parallel RC from the input to ground. At 1/(2piRC), the "gain" of
the series/parallel network is 1/3 at an angle of 0 degrees. Make up the
gain with the amplifier and it oscillates. You can put a small light bulb
in place of the resistor between the inverting op amp input and ground go
get automatic gain control. As the signal gets larger, the lamp current
goes up, increasing resistance and decreasing gain). The lamp probably
won't work at real low frequencies (it will follow the waveform).
       A nice chip for generating sine waves is the XR2206. It has square,
sine, and triangle wave outputs (you switch between triangle and sine).
It has two timing resistors and another pin to select between the two, so
it's nice for generating frequency shift keyed signals. You can also
inject current into the timing resistor pins to do linear FM. It has an
analog multiplier (balanced modulator) in the output, so you can generate
AM, BSBSC AM, and BPSK. The sine/triange output has a source resistance
of 600 ohms, ideal for driving phone lines and stuff.
       Nice chip! I first used it in the mid 1970's.
       Finally, if you want to move to a PIC, for a low frequency, you can use
the PWM output to drive an LPF as a D/A. Then use a sine lookup table to
output values for a sine wave. You could even do "variable phase
addition" in the PIC to do direct digital synthesis... Of course, there
are DDS chips available (for much higher frequencies).

Harold




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2002\02\20@164050 by Nick Veys

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Like page 2 of this document?
mayaweb.upr.clu.edu/~mtoledo/newpages2/ElectronicsII_files/Docs/H
andouts/oscillators.pdf

That seems to be the simplest W-Bridge I've found, and just what you
described except with the feedback on the inverting input...

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> {Original Message removed}

2002\02\21@014851 by Vasile Surducan

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On Wed, 20 Feb 2002, Harold M Hallikainen wrote:

>         Well, you could go with a Wein Bridge oscillator. It consists of a
> non-inverting amplifier with a gain of three (generally made with an op
> amp and a couple resistors), a series RC from the output to the input,
> and a parallel RC from the input to ground. At 1/(2piRC), the "gain" of
> the series/parallel network is 1/3 at an angle of 0 degrees. Make up the
> gain with the amplifier and it oscillates. You can put a small light bulb
> in place of the resistor between the inverting op amp input and ground go
> get automatic gain control. As the signal gets larger, the lamp current
> goes up, increasing resistance and decreasing gain). The lamp probably
> won't work at real low frequencies (it will follow the waveform).

 Or, as I tell you before, a n-fet as controlled resistor, drain to
inverting , source at ground. A small signal diode ( better germanium, but
works also with 1N4148 ) will rectify the output sinusoidal signal and
drive the gate respecting the polarity command voltage through a
potentiometer, small filtering cap to gnd.
A series resistor with drain is required and also may be necessary a
parallel resistor with d-s fet circuit to adjust the gain. Is the best
and stable way from 0.1Hz to 100KHz sinusoidal oscillation, better than
any other solution ( from distorsion performances speacking ) including
8038/max038 family.

best, Vasile

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2002\02\21@150638 by Harold M Hallikainen

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On Wed, 20 Feb 2002 15:38:35 -0600 Nick Veys <EraseMEnickspamEraseMEVEYS.COM> writes:
> Like page 2 of this document?
>
mayaweb.upr.clu.edu/~mtoledo/newpages2/ElectronicsII_files/Docs/H
> andouts/oscillators.pdf
>
> That seems to be the simplest W-Bridge I've found, and just what you
> described except with the feedback on the inverting input...
>

       Actually, it's just what I described. R1 and R2 set the gain of the
noninverting amp to 3. The "gain" of the series/parallel RC network is
1/3, so the amplifier gain makes up for this and it oscillates. I gave
the analysis of the RC network to my students a while back as an
exercise, but do not now find it in my class notes.
(http://www.hallikainen.org/cuesta/)

Harold



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2002\02\25@194813 by Edson Brusque

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Hello,

   as this topic seens to be closed, I just want to tell that I've tried
the Wien-bridge oscilator with a 741 and some cheap 12V lamps I've found on
our local electronics shop and it works very well.

   I'm using the a trimpot to mach the lamp resistance and got very nice
sine waves on the scope.

   Best regards,

   Brusque

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2002\02\26@033943 by Vasile Surducan

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Excellent !
Than you can do some experiments:
- test how much it takes from the power on moment to got final stabilised
oscillation ( amplitude and frequency )
- test what's happened if you switch on and off a maximum accepted load
- test what's happening with your frequency and amplitude if you blow hot
air on your oscillator.

best regards, Vasile



On Mon, 25 Feb 2002, Edson Brusque wrote:

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