Simple oscillator circuit
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From: Michael Robinson on 6 Apr 2010 13:01 "Phil Allison" <phil_a(a)tpg.com.au> wrote in message news:hpekgk$ar0$1(a)news-01.bur.connect.com.au... > > "Gone Fishin'" > >>> Change both R values and both C values together and do not go under >>> 1kohm >>> for R. >>> >>> Many other op-amps could be used, but the NE5534 is a good choice. >>> >> >> So changing both R to 50pF and leaving both R at 100K will give 31.8KHz? > > > ** You must reduce the two R values to a few kohms at most and then pick > C to suit. > > 2.2 kohms and 2.2 nF is about right. > > Fine adjustment can be done with a pot of about 10% the value of R in > series with one of them. > > > > .... Phil > > Could you use a single supply with a voltage divider to set a virtual "ground" node without causing distortion of the output waveform, or would it be necessary to put a voltage follower there?
From: Michael Robinson on 6 Apr 2010 20:11 "Gone Fishin'" <gone(a)fishin.net> wrote in message news:0001HW.C7E103ED00579739B01AD9AF(a)news.eternal-september.org... > This TI app note describes a single-supply wien bridge oscillator, which > helps me with a partial solution: > > < > http://www- > k.ext.ti.com/SRVS/Data/ti/KnowledgeBases/analog/document/faqs/sscco2.htm> > > The note does not describe specific op amp P/N's. Should I limit my design > to > a single-supply op amp? Or can a dual-supply op amp and a single supply be > used here? > > Thanks. > Among conventional op-amps, there isn't much that really makes a single-supply op-amp special. Often the only thing about an op-amp that inspires the manufacturer to call it a single-supply op-amp is the fact that the common mode range (the input) includes the negative supply. At least that's my take on it. More to the point is that your APPLICATION appears to require a dual supply. Almost any old op-amp will do, like the one Phil named or even a good old 741. You need a central reference point for that circuit, as indicated by the ground symbol. It's actually not hard to take a single supply and effectively split it in two. You need a voltage divider and a voltage follower. The voltage divider is two resistors in series connected across your power supply that creates a voltage reference at the midpoint between Vcc+ and Vcc-. But it has high impedance, which means that drawing current from it will drag the voltage up and down, something you don't want. So you put a buffer in there, a voltage follower. If you get a dual op-amp you can use the spare op-amp as the voltage follower. To use an op-amp as a voltage follower you connect the non-inverting input to the voltage divider, and connect the inverting input to the op-amp's output. The op-amp's output is then a low-impedance source at the midpoint of your power supply. It's like taking a 12 volt battery and magically turning it into two 6 volt batteries in series. You can also use a bjt as a voltage follower.
From: Gone Fishin' on 6 Apr 2010 20:28 > Does the output have to be sinusoidal? > > Does it have to be centered around zero volts? > > Does it have to be symmetrical? > > JF Approx 30 KHz, sine, distortion not terribly important. Centered around zero? Don't know. It's to be the input to an amplifier module like one of these? <http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=- 1&storeId=10001&catalogId=10001&productId=23270> Thanks.
From: Phil Allison on 6 Apr 2010 21:04 "Gone Fishin'" > > Approx 30 KHz, sine, distortion not terribly important. Centered around > zero? > Don't know. It's to be the input to an amplifier module like one of these? > http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-&storeId=10001&catalogId=10001&productId=23270 ** The link is to an LM1875 audio amp. One could use that as the oscillator. ...... Phil
From: Bob Masta on 7 Apr 2010 08:47
On Mon, 5 Apr 2010 21:24:27 -0700, Gone Fishin' <gone(a)fishin.net> wrote: >I want a simple oscillator circuit that will give 30 kilohertz. > ><http://tinypic.com/m/9quype/3> > >Which of these components do I change to achieve this? > >What values should these be? > >If I want a little variance (~10 percent) it should be the resistor, right? > >What other opamps can I use? > >Thank you. > You haven't mentioned what your ultimate goal is, but I'm guessing that this is to be part of something that is experimental... maybe in need of some adjustments (the ~10% variance you mention) before you get things to work just right. If so, you might want to use a function generator during the development phase. Then when you are sure you can get the desired result, you can replace that with a circuit. If you don't already have a function generator, you can use the free Daqarta Generator, which works with your Windows sound card. To get to 30 kHz, you'll need a sound card (or built-in chipset) capable of sampling at 96 kHz. Most systems will do that these days, but older systems may be limited to 48 kHz, or even 44.1 kHz if it is *really* old. Sound output frequency on any digital system can't exceed half the sample rate, but at 96 kHz you should have no problems getting to well past 30 kHz. Note, however, that there are some systems that can sample at 96 kHz, but which apparently have analog filters that limit the output frequency to ~20 kHz. You can easily test if yours is one of these via a "loopback" cable from output to input. Although this may all sound rather cumbersome compared to a neat little circuit on a breadboard, the advantage is that you can easily change things experimentally. Besides fixed-frequency sines, you can change waveforms at the click of a button, or add various types of modulation (AM. FM, Phase) or tone bursts or sweeps. You can even create a band of noise that covers a chosen frequency range. Then, once you find the ideal signal for your project, you can cast it into hardware. Otherwise, if you start with the hardware and the initial design doesn't give the desired results, you can waste a lot of time pursuing dead ends. For example, if you think *maybe* it would work better with an FM warble, that's not easy to add to your existing design. But if you knew from the function generator tests that it was needed, you could get the right circuit for the job. Note that the Daqarta Generator really is absolutely free. After the trial period, the *inputs* stop working unless you buy Daqarta, but the outputs (ie the Generator) will keep working forever. Enjoy! Best regards, Bob Masta DAQARTA v5.10 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI DaqMusic - FREE MUSIC, Forever! (Some assembly required) Science (and fun!) with your sound card! |