[HN Gopher] It's hard to build an oscillator
___________________________________________________________________
It's hard to build an oscillator
Author : chmaynard
Score : 208 points
Date : 2025-11-21 07:45 UTC (15 hours ago)
(HTM) web link (lcamtuf.substack.com)
(TXT) w3m dump (lcamtuf.substack.com)
| atoav wrote:
| Coincidentally I thought a class of art students just yesterday
| how to build oscillators. And it is not hard at all. Take a logic
| inverter IC (CD40106 Schmitt-Trigger Hexinverter) pick a single
| gate, connect the output to the input, add a capacitor from the
| input to ground. That is it. Three parts and you got a Relaxation
| Oscillator. And then you have 5 inverter gates left.. But of
| course one could argue ICs are cheating, since any PLL-IC would
| have an oscillator onboard.
|
| Why the first two circuits fail is also pretty obvious without
| derper circuit analysis: to get _reliable_ oscillation you don 't
| only need amplification, you also need some time setting element,
| usually in the form of a capacitor (or involuntary capacitance).
| eternauta3k wrote:
| Relaxation oscillators are easy, good phase shift oscillators
| are an art.
| eternauta3k wrote:
| I was hoping this would go more into startup and amplitude
| control, which are for me the tricky parts of building a phase
| shift oscillator (because you have to analyze the non-linear
| behavior).
|
| I guess hobbyists nowadays are just using SI5351 and calling it a
| day.
| Joel_Mckay wrote:
| Most use GPSDO references for equipment, as they are
| inexpensive. Even miniature TCXO tend to still offer quite good
| value these days. =3
| kurthr wrote:
| Building an oscillator is "just" putting some gain around a large
| enough phase delay (>90deg). The challenge is in making the
| oscillator predictable and STABLE.
|
| You want a frequency generator that oscillates with a constant
| period/frequency. Even an unbalanced oscillator can just be
| divided by two to provide uniformity. However, it turns out that
| building something that is not sensitive to any outside inputs
| (temperature, strain, voltage, time, etc) is really hard to do
| over a very wide frequency range (from ~DC to many MHz), but from
| that you can build a stable clock.
|
| Look up Allan Variance, if you're looking for bit of a rabbit
| hole on clocks and oscillators and other sensors.
| fuzzfactor wrote:
| Exactly, all that you needed to do was "draw the rest of the
| owl".
|
| >It's hard to build an oscillator
|
| It took a long time, too, after the invention of the vacuum
| tube.
|
| Finally one day they had some remarkable success using
| circuitry more reliable than ever before.
|
| It seemed so promising that a startup really could be based on
| technology like that, so that's what was happening.
|
| Unless you were intrigued by relatively high-voltage analog
| electronics, it was just another boring engineering company.
| Even though they were very creative, their little company was
| simply named after the founders like many others.
|
| That's why they called their startup Hewlett-Packard.
| dvh wrote:
| It's super easy to build LC oscillator.
|
| I made a program that generate random topology and uses spice
| simulation to find if it oscillate. The goal was to find some
| novel LC oscillators. It worked, it found many different
| oscillators. I let it ran for a while and soon I found out that
| the simplest possible LC oscillator has 1 inductor, 2 capacitors,
| 1 resistor and 1 transistor. I found many different variations of
| it, I called this class of oscillators "LCCRT oscillator" and it
| also always had 2 internal nodes so that's not very large search
| space (40000 combinations) so I generated all possible
| combinations and I found out there are exactly 12 distinct LCCRT
| topologies.
|
| Basically any time cap connects to a rail it can be placed to
| other rail as well, and any time one rail connects via resistor,
| the resistor can also be moved to other rail. This creates 12
| possible combinations. I tested them in real life and they are
| stable, even used one in metal detector.
|
| Of course it found many different topologies. Some times they
| were unique, other times they could be simplified into already
| found oscillator. It can also use multiple transistors not just
| one. You can find entire project on github, it is a ngspicejs
| script: https://github.com/dvhx/lc-oscillator-finder
| amelius wrote:
| Nice! Perhaps you could sort them based on Q-factor.
| webdevver wrote:
| this is always the risk of posting on hackernews: a random
| commentator absolutely iq mogs the op.
| seg_lolr wrote:
| "Novel". Those are all Collpits LC oscillator variants, circa
| 1918. All LC oscillator topologies were thoroughly investigated
| more than a century ago, hundreds of books have been written
| about them. A little more humility please
| ofalkaed wrote:
| Passive circuits have been novel for a long time now, or at
| least very very quaint. It is hard to put much stock in a
| coil when it is banal to walk around with 100 billion
| transistors in your pocket.
|
| One of my favorite books is Tremaine's Passive Audio Network
| Design, seems appropriate right now. Passive circuit design
| is great fun and a lost art.
| goopypoop wrote:
| "novel" means new, not rare
| ofalkaed wrote:
| Novel is considerably more complex than just new and even
| new is more nuanced; your new car could be as old as the
| Colpitts oscillator. Novel carries with it the unfamiliar
| and how that unfamiliarity alters our perception of what
| was once familiar. When you drive about in your new Model
| T everything is different, you are sitting considerably
| higher than you do in your old 240Z that you have driven
| since 1973 and its vertical windshield gives a far more
| limited view, its lack of power steering makes you aware
| of how sharp those curves in the road are and everyone
| notices you when you drive by. Then you take you old
| Datsun on a milk run and now it is more familiar than it
| was, you are aware of how intimately you respond to it
| and it responds to you but also of how its power steering
| removes some of the intimacy of driving and people stop
| talking to you about what you are driving because you
| have been driving that car since 1973 and everyone knows
| you as the person who has driven the same care since
| 1973, they ask you how your day is instead of
| complimenting your antique car. But the novelty
| eventually wears off and the old Model T becomes as
| familiar as your 240z.
|
| Most in electronics never learn to drive without power
| steering, they view passive circuits as simple little
| things that need active components between them so they
| don't interact with each other in maddening ways but
| those interactions are not maddening once you understand
| them and learn to exploit them.
|
| I don't think anyone used novel to mean rare.
| jfengel wrote:
| As a CS guy who got the absolute bare minimum introduction to
| electronics: why isn't the article about LC oscillators?
|
| I get the impression that there was some requirement to use
| transistors that I was missing. The article briefly mentions
| some kind of inductor as a rare component.
| the__alchemist wrote:
| Hah! As an IC baby, I assumed it would be about what goes on
| inside crystal oscillators, TCXOs, MEMS oscillators, the
| difference between the one that you add 2 caps to with in and
| out vs the ones that don't need In and use a single bypass
| cap.
| tlb wrote:
| Inductors (the L of LC) are large and expensive except at
| very high frequencies. So audio circuits are normally
| designed with just resistors and capacitors.
|
| And you always need an active component like a transistor. A
| pure LC can oscillate for hundreds of cycles but not
| indefinitely.
| achr2 wrote:
| This is really great, both from a specific application
| perspective, but also the approach. Really enjoyed looking
| through the repo and was inspired by your work.
| Mizza wrote:
| Never found it hard to build an oscillator, the hard part is
| musical voltage per octave. 3340 repro chips are the way to go,
| the best non-3340 circuit I've seen is this one and it's still
| temperature-sensitive:
| https://www.youtube.com/watch?v=FiCMjt0mqvI
| ofalkaed wrote:
| Temperature sensitivity only matters in polysynths where you
| don't have easy access to per-oscillator tuning. It is not
| difficult to build an oscillator with better pitch stability
| than a guitar, even my VCOs with no temperature compensation
| require less tuning than any guitar I have owned.
| Mizza wrote:
| But that's for synths where the oscillators are ICs. I'm
| talking about simple oscillators from basic components
| ofalkaed wrote:
| My VCOs which lack temperature compensation are oscillators
| built from basic components. The closest I have to
| oscillator on an IC these days, are the VCOs in my Moog
| Prodigy which use a quad OPAmp and a 3086 transistor array,
| it is far more stable than any guitar string.
| elihu wrote:
| 3340s are great. I've also heard good things about the SSI2130
| and 2131 chips as a more modern alternative to 3340.
|
| 3340s are more DIY-friendly though, as they're DIP packages.
| reactordev wrote:
| As someone with a CS degree and not an EE degree, this is
| fascinating. I tried a decade ago to build some simple RC lights
| controller circuit that would operate off of a PWM signal and
| failed. Hats off to you hardware folks. Manipulating atoms and
| electrons and building circuits that allow us to play games,
| build businesses, communicate with loved ones, and write this
| post.
| ofalkaed wrote:
| When I was starting out in electronics I found the easiest way to
| build an oscillator was to build an amplifier and the easiest way
| to build an amplifier was to build an oscillator. I guess the
| trick is to be 7 years old and have far more ambition than skill.
| Couldn't guess at how many tries it took me to make an amplifier
| that didn't oscillate and when I moved onto oscillators, they
| never oscillated but they did amplify. In that first year or so,
| I couldn't actually read resistor color codes, but I thought I
| could.
| seg_lol wrote:
| > the trick is to be 7 years old and have far more ambition
| than skill
|
| Never lose this
| hollerith wrote:
| Apologies for my bluntness, but in my humble opinion,
| American society would be better if it had fewer adults like
| this.
| ofalkaed wrote:
| Being able to enjoy and find worth in the process
| regardless of the outcome is bad? Are we man-children if we
| don't treat everything as if it were as serious as cancer?
| I'm not really sure what you are trying to say.
| immibis wrote:
| Ambition develops skill. One of the problems with American
| society is people thinking they have skill when they don't.
| If people knew they had ambition and no skill, they'd try
| things and learn.
| majorchord wrote:
| Dunning-Kruger actually applies to everyone, especially
| to people who openly and over-generalizingly criticize an
| entire nation's supposed lack of skill.
| fragmede wrote:
| that's a helluva thing to just drop. What are your priors?
| Are you American yourself, or living in or near it? In what
| way would it be better? How so?
| hollerith wrote:
| Yes, American citizen living in the SF Bay Area.
| taneq wrote:
| I think the scenario of childlike wonder and limitless
| ambition is a little different to the scenario of embraced
| ignorance and wilful misrepresentation of any surviving
| facts in furtherance of the agenda du jour.
| jacquesm wrote:
| Yes, but then again, we could make a very similar comment
| about Hackernews.
| JKCalhoun wrote:
| You are likely talking about a different aspect of _child-
| mindedness_ than the person you were responding to.
| eru wrote:
| Why talk about Americans now?
| hollerith wrote:
| Only because I don't know the rest of the world well
| enough to say.
| fuzzfactor wrote:
| Wait until you see what some of the people in other
| countries do when they try to imitate Americans.
|
| It makes you think, why even bother?
|
| Not my downvote BTW.
| HeyLaughingBoy wrote:
| Ambition should always outpace skill. Otherwise, how would
| we get anywhere?
| taneq wrote:
| Often the biggest thing holding you back from doing something
| is the sensible, mature understanding that it's impossible.
| dylan604 wrote:
| Growing up, I never had the budget of a _real_ TV studio, but
| had equipment that would approximate a _real_ TV studio. I
| would come up with ways to recreate what they were doing
| because it could clearly be done, but by using totally
| different equipment that only looked like it was up for the
| task. Asking the _real_ TV people if it could be done, they
| 'd say no. I'd say hide and watch (too young to have a beer
| to ask them to hold).
|
| Sometimes, the box a degree stuffs you into with all of that
| _learning_ often means losing some creative out-of-the-box
| thinking abilities. I get away with things all the time
| because I didn 't know you weren't supposed to _not_ do this,
| yet now that I _have_ , it works just fine.
| fallous wrote:
| If you combine a 3 year-old, whose favorite word is "why?", and
| the ambition of a 7 year-old you might just end up with the
| most productive genius possible.
| IAmBroom wrote:
| Add the social insecurity of a pubescent, and you suddenly
| have a madman knowitall (with almost no actual knowledge)
| that slows that learning to a drip.
|
| It's a miracle high schools are able to achieve anything,
| really.
| IsTom wrote:
| I wish Esaki oscillator was mentioned. It's a funny bit of
| trickery.
| a5c11 wrote:
| One of my favorite is an RC circuit with a Schmitt triggered
| inverter. So simple and ingenious.
| Marazan wrote:
| It is beautifully simple and a classic building bloc of Lunetta
| music synths
| ErroneousBosh wrote:
| > There's an old electronics joke that if you want to build an
| oscillator, you should try building an amplifier
|
| It's funny, I was just thinking this morning about an old article
| in (I think) Television magazine that I read in the 80s when I
| was getting into electronics. The author was talking about some
| service notes he'd received for a particular model of Philips
| radio, which had just come out, and it was when shops tended to
| have their own service department that would repair things right
| there in the shop - and also, apply any "factory fixes".
|
| One such fix was described as "Fix VIUPS", and involved changing
| a couple of resistors and adding a couple of capacitors. Not
| really any difference, but the author did think it seemed to make
| the amp a bit more stable and less inclined to make squealy
| ploppy noises at high volume when the battery was low. But,
| curiosity got the better of him, so he rang the Philips rep -
| what's this "VIUPS"?
|
| No idea. But I'll get hold of someone at head office you can
| ring. Okay, what's this "VIUPS" thing? No idea, said the head
| office guy, but I can put you in touch with one of the factory
| engineers in Eindhoven.
|
| So, a call came in, an international call! Quite a big deal in
| the 80s. "What's this VIUPS Fix thing in the service notes?" he
| asked the guy.
|
| "Aha yes", he said in a heavy Dutch accent, "the VIUPS is the
| noise the set makes when the fault is present."
|
| VIUPS VIUPS VIUPS. Yup.
| Zardoz84 wrote:
| > There's an old electronics joke that if you want to build an
| oscillator, you should try building an amplifier
|
| The most easy way to annoy a neighbor using AM radios, it's
| using a regenerative AM receptor with too high gain. Could
| oscillate and begin to emit noise at the same freq that are you
| tuning. Adding a simple carbon microphone to it, and setting
| the gain to the max, was a very easy way of building a AM radio
| emitter.
| IAmBroom wrote:
| Pretty sure just blasting that rock and roll "music" out the
| window is easier.
|
| Damn hippies.
| ErroneousBosh wrote:
| I once made a guitar amp that oscillated pretty well at
| around 100MHz, sufficient to wipe out one of the FM radio
| stations for about half a mile radius.
| buescher wrote:
| > There's an old electronics joke that if you want to build an
| oscillator, you should try building an amplifier
|
| The way I heard it was "amplifiers oscillate and oscillators
| don't".
| dbcurtis wrote:
| The way I've heard it is: Being a microwave engineer is the
| easiest job in world. You basically only do two things,
| design oscillators and design amplifiers. What's the worst
| thing that can happen to an amplifier? It oscillates! And
| what's the worst thing that can happen to an oscillator? It
| won't start, but it's usually still a pretty good amplifier.
| Win-win!
| B1FF_PSUVM wrote:
| "The fears of a designer are amplifiers that oscillate and
| oscillators that don't."
| nullorempty wrote:
| Yea, that resonates!
| severak_cz wrote:
| > There's an old electronics joke that if you want to build an
| oscillator, you should try building an amplifier
|
| This can be easily demonstrated using so called no-input
| technique[0] which basically means that you patch audio mixer
| output to it's input and it starts feedbacking and you can
| create some tones from this. Note that this needs to be done
| carefully.
|
| [0]: https://www.youtube.com/watch?v=H-7kQmpjBds&t=2s
| lm2s wrote:
| For anyone interested in this kind of stuff with a music oriented
| gist, a while ago I found this awesome YouTube channel:
| https://www.youtube.com/@MoritzKlein0/
| jnovek wrote:
| I couldn't see the whole link on my phone but I knew it would
| be Moritz Klein.
| ZyanWu wrote:
| What intrigued me was the "just use a microcontroller" comment at
| the bottom of the page - I genuinely don't know if it was pinned
| because it's a joke, a genius idea or just top 10 dumbest
| comments of 2025
| dgacmu wrote:
| The comment is by the author. And it's not wrong! You can get
| super cheap microcontrollers for pennies that will act as an
| easy to use programmable oscillator, if that's what you want.
| And more to the point, you usually want an oscillator to _do
| something_, not just to wiggle in isolation, and the cheap
| microcontroller lets you skip the middleman in many cases.
|
| Yes, you're using a million transistors to do something you
| could have done with a couple of discrete passives, but it will
| often result in a lower total BoM and development time. Not
| always.
| ZyanWu wrote:
| Well, it's a bit of a chicken and the egg, no?
| Microcontroller won't work without a (most likely) crystal
| oscillator or something to act as a clock signal.
|
| Now that I think about it, no, it's not even cheaper as XTALs
| are quite pricy compared to other discrete components.
|
| I didn't mean to be rude - I interpreted the comment as
| "Would you like to build an (insert random object here)?
| Well, you can just BUY it and be done with it" - may not be
| as I put it (dumb) but certainly... simplistic and purpose-
| defeating
| mindcrime wrote:
| There is always
| https://en.wikipedia.org/wiki/Direct_digital_synthesis, FWIW.
| ErroneousBosh wrote:
| Two things not mentioned - hey maybe I should blog about these
| myself and post them up?
|
| The first being the "Two Transistor Metronome" that I can't even
| remember where I saw first - possibly Electronics Today
| International or Hobby Electronics, although Practical
| Electronics was a contender - we didn't get that one much though.
| I remember my dad and I building this when I was probably about
| seven or eight, and I've built loads since.
|
| https://tinyurl.com/22qjecj7
|
| It's a relaxation oscillator where the two transistors form more-
| or-less an SCR, which fires when its (negative-going) gate
| voltage exceeds its anode voltage. Kind of.
|
| A similar circuit using three transistors and a diode is used in
| the oscillators in the Roland TB303 and Korg MS10/20/50 series,
| with a current source used to set the capacitor charging time so
| you get a nice linear sawtooth. Conveniently the expo converter
| turns an incoming control voltage into an exponentially-rising
| current, which is just what you need!
| JKCalhoun wrote:
| I was thinking Astable Multivibrators. Probably the same as
| your Metronome. The circuit I usually see uses two NPN
| transistors instead of the PNP+NPN your metronome does:
| https://www.electronics-tutorials.ws/waveforms/astable.html
| ErroneousBosh wrote:
| It's a different principle, although I have a Ladybird Book
| of Electronics that my dad gave me when I was just about the
| age my son is now, that shows how to make a thing that
| flashes two lightbulbs using that astable circuit (and a few
| other things).
|
| The two-transistor metronome one really is working more like
| an SCR, that rapidly charges the capacitor and allows it to
| discharge again.
| temp0826 wrote:
| As the famous one-liner from EE goes- if you want to build an
| oscillator, build an amplifier; if you want to build an
| amplifier, build an oscillator.
| nrhrjrjrjtntbt wrote:
| Then it is you that bends, not the spoon.
| fjfaase wrote:
| I remember creating an oscilator by soldering a transistor onto
| an inductor with two windings in series with loudspeaker an
| battery.
| Zardoz84 wrote:
| > The circuit can be simplified to two transistors at the expense
| of readability, but if you need an analog oscillator with a lower
| component count, an operational amplifier is your best bet.
|
| Well... Using a NOT (really a NAND) gate was a very classic way
| of generate clocks for discrete logic.
| fsckboy wrote:
| he said "if you need an analog oscillator". (yes, digital
| signals are analog signals and analog signals are digital
| signals, but...)
| highspeedbus wrote:
| I've build a signal injector to debug a guitar pedal that was not
| working. It was a nice little journey in itself. The astable
| multivibrator produces so much harmonics that I could hear it all
| the way back from the input jack, where it was supposed to be
| silent. Heck, I could hear it just by putting the probe nearly
| close to the circuit. The signal pushed through the circuit like
| Juggernaut breaking walls. Learned a lot about filters and was
| able to produce a nice sine wave out of it, it worked great.
| jhallenworld wrote:
| Easy negative resistance oscillator: a neon bulb in parallel with
| a capacitor connected to a DC power supply through a resistor.
| IAmBroom wrote:
| "Negative resistance"? Are you sure that's what you mean? Cuz
| it isn't.
| jhallenworld wrote:
| Yes, it is... (negative differential resistance to be more
| precise)
|
| https://en.wikipedia.org/wiki/Pearson%E2%80%93Anson_effect
|
| https://en.wikipedia.org/wiki/Negative_resistance
| zhrvoj wrote:
| I built many such oscillators same way. But I used BC107 NPN,
| connected collector to the ground, emmiter to
| resistor/capacitornet. Base free. Add LED in series with such
| connected transistor, and you have LED blinker.
| stevetron wrote:
| In some reading I did several (decades) years ago, I read how the
| invention of the oscillator was an accident. Someone was building
| an amplifier, and made a wiring error that was described as
| connecting the amplifier's input to the amplifier's output and it
| produced a squeal.
|
| Up until that time, radio frequency carriers were produced with
| AC Generators designed for a high-frequency (> 60 Hz) output.
| That is in part why it took so long for things like music to be
| broadcast by radio: you needed a high-frequency carrier.
| Generators were topping out at about 15K Hz according to the old
| article I read.
|
| So once they had the accidental circuit that squealed, it was
| studied and expermented upon (trial and etrror modifications),
| and that is where all the 'classic' oscillator circuits
| originate.
|
| Essentially, an oscillator is an amplifier with positive
| feedback. Amplifiers that are amplifiers sometimes have negative
| feedback.
| readingnews wrote:
| It is hard to put into words how so many people "out there" can
| print things, have people read them, and they are so worded that
| the average person is probably reading this as "the truth".
|
| > but it's rather difficult to build a good analog oscillator
| from scratch. The most common category of oscillators you can
| find on the internet are circuits that simply don't work. This is
| followed by approaches that require exotic components, such as
| center-tapped inductors or incandescent lightbulbs.
|
| It is not hard to build a good analog oscillator from scratch, we
| have been doing this for decades. Secondly, while an incandescent
| _might_ be considered exotic, and completely unnecessary for an
| oscillator, a center tapped inductor is totally not exotic, and
| also, not really necessary for an oscillator.
|
| As others have noted, it is simple to build a really good analog
| oscillator. This article is blah, and "meh" at best.
| parsimo2010 wrote:
| It's great to do experimentation because you get to learn a lot,
| but at the end of the day stick with well-studied designs if
| you're making a something you want to use. The oscillators
| mentioned below all have well known strengths and weaknesses:
|
| The author mentions that they consider a center-tapped inductor
| to be "fancy," but if you consider a regular inductor to be fair
| game, then the Colpitts oscillator is a good choice. And I
| suppose you could build a Hartley oscillator with two inductors
| rather than one center-tapped inductor.
|
| If you consider op-amps to be fair game even though it is made
| from multiple transistors, then you might consider digital logic
| to also be fair game and should consider a Pierce oscillator. I'm
| also assuming that a crystal is also fair game, but those are
| quite cheap.
|
| Side note- these oscillators are all part of the exam material
| for the Extra class amateur radio license in the USA. If you find
| lcamtuf's Substack interesting, then amateur radio might be for
| you.
| kazinator wrote:
| It's not hard to build an oscillator. Just focus on designing an
| amplifier, and stop _chasing_ oscillation.
| crmd wrote:
| The bring up of seemingly every tube guitar amp i've ever built
| starts with wild oscillation due to negative feedback from the
| wrong transformer secondary, aka positive feedback. Gets me every
| time.
| summa_tech wrote:
| I wanted to give a quick explanation of the odd and off-hand
| "lightbulb" comment in the article. Why would an oscillator need
| a lightbulb? Especially since the article does not get into the
| weeds of building oscillators that would actually care about
| this.
|
| A somewhat difficult part of making (moderate-frequency) analog
| oscillators is getting a clean sinewave without harmonics. It
| sounds like the easiest thing in the world: a delay, a low-pass
| filter, a linear amplifier that compensates for the loss in the
| delay and filter, and boom, sinewave. You can even put the low-
| pass filter and the delay in a single phase shifter circuit.
|
| The difficulty is hidden in the "compensates for the loss"
| language. If you amplify too little, your oscillation will decay.
| If you amplify too much, you will inevitably saturate the
| amplifier, introducing lots of harmonics (like a squarewave
| output in the article). So you need some way to stabilize your
| gain at exactly the right level.
|
| A lightbulb is an interesting device: it is a very linear
| resistor at short timescales, but nonlinear at long timescales.
| As the filament heats up, resistance rises. The thermal constant
| can be fairly substantial, certainly more than kHz or MHz
| oscillator frequencies. So you can exploit this sweet and clean
| nonlinearity to produce an oscillator that self-stabilizes!
|
| Design your circuit so that the amplifier gain is controlled by
| lightbulb's resistance (which is quite easy: you use the
| lightbulb as one of the gain-setting resistors). And boom, pretty
| much a perfect sinewave.
| JJMcJ wrote:
| Also if it oscillates does it oscillate at the frequency you
| want?
| dragontamer wrote:
| Oscillators are hard because our specs on oscillators are absurd.
|
| Let's take the common watch circuit. Conceptually it's just like
| 5 components: crystal, a few capacitors, a NOT
| gate/transistor/amplifier. Introduce 180-degree phase shift at
| the 32.768k target frequency and bam, oscillator.
|
| Except not really. A clock is expected to have a drift in the
| region of 100 ppm (or 0.001% error), or lose a second per day or
| so. That's the hard part, building something that accurate and
| consistent.
|
| There are also startup specs, power specs (less power is harder.
| More power helps startup....) etc. etc.
|
| -------
|
| If you just need something to oscillate back and forth randomly,
| try making a noise generator lol, it will oscillate wildly at
| many frequencies, one of which might have been the frequency you
| wanted.
|
| ---------
|
| The 555 timer is perhaps the easiest oscillator for a beginner if
| you are willing to put up with +/-10% drift. It's honestly good
| enough for far more applications than you might expect.
|
| Even without the premade chip, a 555 timer is just 2x comparators
| (analog version of an If statement), a 33%/33%/33% voltage
| divider, and a capacitor. If Voltage > 66% input voltage, remove
| power from capacitor. If Voltage < 33% input voltage, add power
| to capacitor. Bam, you now have an oscillator that is accurate to
| the +/-10% capacitance values of your electronics kit.
|
| Alas, modern circuits need to be faster and more accurate than
| the humble 555. But a beginner article about oscillators should
| be about the 555, rather than about opamp or transistor based
| oscillators.
| ur-whale wrote:
| My all time favorite analog oscillator is the Twin-T (the one
| with a BJT) [1]
|
| It was hard to get a proper intuition of how and why it works,
| but when you finally do ... fireworks!
|
| Another thing that's real fun with oscillators is to try and
| build a true chaotic oscillator, but only with R+C+BJT
|
| Not easy, but can be done [2]
|
| [1]
| https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj...
|
| [2] https://www.instructables.com/A-Simple-Chaos-Generator/
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