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How to build an osscilator that gives me 440Hz and connect it to an Speaker? Answered

We want to build an oscillator (440hz) that uses an 9v Battery block and would like to hear this Signal with an Loudspeaker. What do i need to know about the loudspeaker?


Hallo again it took a long time for me

first i tried the LM101 and LM111 but i failed - dont know why
but after checking around one month i was ready and
yesterday i went to my local elctronic store and bought an XR2206
and it works very fine its exactly what i want so it  was a good lesson to learn


8 years ago

OK, if you want to avoid an all-in-one chip, then check out this application note from National Semiconductor:


Using two op amps and a few discrete components you can build a nice low-distortion sine wave generator that is easily tuned to your desired frequency. Figuring out how the circuit works would be a great learning experience.

You can use an LM301 in place of the LM101, and an LM311 instead of the LM111 - the 100-series is just the high-end military grade version (and is much more expensive).

Hi i just returned from my local electronic part dealer where i got everything so thanks for your help. But there are two further questions i have. The +15 and the -15 what is it? is it the VCC for the op amp that he needs to amplify? And the second where i wrote Probe are the points where i have to put the probe of my oscillograph to detect the signal? And if i would like to use the signal for an speaker i would return it to the ground after usage? And anotherone LM 311 gives me an square that LM301 converts to a sine? I hope not to many questions :-) Thanks Jakob


First off, the "probe" points. Yes, this is where the signals are measured on a scope, and where you'll eventually connect a speaker. The other end of the speaker would indeed connect to ground. I'd suggest placing a DC-blocking capacitor at the outputs to prevent DC voltages (if any) from damaging the speaker. +15 and -15 are the voltage rails. It will run best with a +15, GND, -15V supply, but it should work fine with two 9V batteries too. Attach the batteries in series and center-tap the point where the batteries connect to get +9V, GND, and -9V. As for how it works, I suggest reading the application note over carefully. It will explain things better than I can. :)

Hey that sounds good!!!
And have here an 12V powersupply wich is not stabilised and i also bought an (http://www.national.com/mpf/LM/LM1086.html) to drop the voltage to 15 Volt but it is DC so +15 is the positive and -15 is the negative i have to put onto the opamps - ore?

It's just a plain +12V DC adapter that plugs into the wall? You can't use that unless you have two, then you can connect them together to form a +12, GND, -12V supply. But really, it would be easier to use an old computer power supply. It already has all the voltage rails you need. There are a few instructables on how to convert a computer power supply into a lab bench supply.

Yeah it is that kind :-( Okay i will work on it (computer supply) thats a great experience!!! If i would use the two 9volt batteries it would look like the picture?? Thank you


Yup, that is exactly how you'd hook them up. The + would go to the +15, and the - to -15. GND is, well, ground.

cool - hihi - now i can start! its only two weeks ago that i thought about building something - and now this is the my second project and it really looks good - thanks for your help guys!!!!!!!

I hope it works! Be sure to carefully recheck your connections before you apply power. It's easy to get excited and plug it in without checking, but that's how burned components happen!

ok i will do so i also had my first learning lessons by burning an led it wasnt in line with the forward resistor but bypassed Jakob

Also, note that it doesn't show power supply connections for the LM101 op-amp. You do need to hook up power to this chip; check its data sheet to see where +15 and -15 are supposed to connect (or in your case, +9 and -9).


8 years ago

Use an XR2206 function generator IC. It's probably overkill, but it will easily generate a 440Hz sine wave for you, at whatever amplitude you want. You could attach a small speaker directly to the output, or to a larger speaker through an amplifier. Another way would be to use a 555 timer (which generates a square wave) and pass the output through a few filter stages to get a sine wave. Does it need to be portable using a 9V battery, or can you use a computer to generate the tone you want?

i think the XR2206 would really be overkill and maybe to complex for the start. We are lerning for our electronic lessens and while we were learning we thought "fu** all this is just theoretic lets build something!" so i came to this Idea to build an osc. circuit. And if we would use the IC the Idea of learning first the "simple" stuff would not work - i think. But thanks for your answer because the Idea with the filter is cool - so what kind of filter would we need to go along with the square wave?

you change it into a triangle using an integrator after the square wave generator, then you wave shape it with stepped conversion (usually requires using zener diodes in the feedback path of the second-to-last amp stage...finally, you push it through a bandpass to make it smooth and pretty...basically everything that the Max038 and its predecessor the intersil 8038 did on a single chip solution (mit a few external resistors, caps, and trimmers for setting ranges and tuning the waveforms)

Yeah, that's pretty much it. See, the reason I suggested the XR2206 first is that it also does all of this for you, in a single IC package with very few external components.

I don't think it gets much simpler than THIS

Oh, I agree about the XR2206...I'd rather use a chip any day over pissing with 1950's circuits. and lol, yeah, about the kit...but i think part of it is that they want to actually design/build something from scratch...can't get any easir than the fundamentals of 555 timers....they're so useful that every new e-designer should start with them (and op amps) imo.

fwiw, I've built waveform generators using all those sub stages....instructive at the EE201 level, yes, no question, but desired for "use"?...not on your life...gimme a single chip like the Max038 or XR2206...

I wouldn't write home to mama, but if you don't need high quality audio it should be just fine... (Audio testing usually requires a very pure tone)

Although neither produce what I would consider High audio quality, I was going to suggest the MAX038, or fail that, the ICL8038, but they have both apparently gone the way of all things good and wholesome.

Do you *require a sine for your application?

Either a square or triangle will still produce an audio tone, just not quite as ...smmoooooooth (a little more like a techno keyboard)

if you don't need a sine, then a 555 is the cheapest and simplest solution . they cost all of 25-50cents apiece and they are ubiqitous (everywhere)

And you can power them directly off the 9v and drive a small set of cheap headphones direct as well (those 3-5 buck deals at the local drug store dollar store?). just put an adjustable attenuator on the output to reduce the peak to peak (you;'ll get 9V p-p square wave out.... you know what a resistive voltage divider is?...

you got it. yup...except R2 would be replace by a pot for volume control...you can figure out (ballpark) what the typical drive voltage is by checking the headphone output of an MP3 player or similar at max volume, using a low AC voltage setting on your DMM.

The exact transfer calculation is a bit more complex (the one is a sine the other a square wave, and the DMM measures RMS values, which have to be calculated differently for sines and squares), but this should get you on the right track empirically.

The trick will then be in selecting both resistances (R1, R2) so that you get sufficient drive current for the headphones without trying to pull too much from the 555. try for

Vin/(R1 +R2) = ~20mA max...

I *think that should do it., but the values may have to be adjusted depending on your results....(you could always measure what the speakers actually require by monitoring their current draw when powered by the MP3 player at full volume, but that's an exercise that I'll leave for you...)

Then select the ratio of R1 and R2 using the voltage divider equation so that when the pot is at maximum, Vout is that value.

best wishes

440hz because it is the "C" but thats not so important.
And my basic idea was to built it as simple as it can be with an capacity and an inductivity (oscillating circuit) - and i think that gives me an sine. And the frequence i can estimate with the equation f=1/2*Pi*sqrt(LC).
To power the circuit i want to use 9v DC (i hope that works) from that battery
So my problem is that i dont know how to hear the signal that this circuit creates. And thanks for the answers so far.

Im only beginning with this electronic stuff so maybe some of my thoughts could be wrong.

gotcha on middle C.. Simple is a relative term. An RLC circuit might resonate, but in all honestly, it is not the simplest way to create a 440Hz tone, especially if you want to hear it.. I'd look up 555 timer circuits here or on the web in general. they can be run directly off the 9V and will power a small set of headphones with the right components used....Much simpler in the long run, unless you're doing homework? Just because it has three components doesn't make it the simplest. It simply means the most primitive.

Why 440 Hz? And why a sine vs a triangle or a square?

The sine wave will be pure 440Hz, the square will contain harmonics up to the limit of hearing (see the amazing transforming Mr Fourier) Steve

True if he spends a bundle on his sine source...audio quality sine costs a pretty penny.

Two guys called Hewlett and Packard did something to do with audio oscillators a few years back, I wonder what happened to them ? Really pure sine ? Hartley or Colpitts oscillator. One transistor, three caps and an inductor.

I rescued one of their early function generators from a local university's trash bins back in the early 1990s... A model 200SR tube driven sine generator ... By today's standard...eh...but I keep it for a really big dial that I think is cool. I'll probably restore it one of these days...kinda unusable right now because of wiring and mechanical issues. The dial barely moves, it puts out signal, but then it stops, then you hit it, then it works...then it stops...also smells like a cleaning is in order but my plate's full of other issues right now. Yes Hewlett and Packard did, but they weren't up against the big green machine, which can produce for a tenth of what it costs me.

Yes you are right im sorry i got something wrong :-)

Ok i understand so i will have a closer look at this 555 Timer Thanks

Hi thank you for your answer! - I will work with it it looks good! But only for understanding i have a further question. I thought that i could use something simple as i painted. Does it also work with this? Am I right that this is an simple osscilating cirquit that should give me an signal that osscilates? I thought that i only must apply an speaker to it an some resistor to hear the signal?


Here's a link to a simple circuit.
As built it will probably osc. at about 300 hz. so you might have to tweak it to get to 440 hz.

You'll have to have some way of measuring the freq. of any circuit you build. The tolerances of the parts are not perfect and the freq. will be an average of the parts. Some dig. multi meters will do freq. measurement.

If you only have to be close, electronic guitar tuners can be used to tune your oscillator.

Also I think 440 is A above middle C if I remember correctly.


8 years ago

sine or square wave?