This isn't a homework question, but it is educational and fits better here than in the Education category. Decades ago, before the internet, I lived in rural Alaska and there was this older fellow who sometimes built circuits that sometimes worked. He was the only person within about 100 miles of air travel (there were no roads) who knew anything about electronics. I wanted a timer for a DC motor driven off a battery and he told me that you could connect a resistor and capacitor to a DC source (a 9v battery I believe he said) and somehow get behavior similar to a stripped down 555 out of it.

Years later I know a bit more than I did as a kid. I'm not an EE, but I build circuits on a regular basis. I can make this work by adding other things in specific applications, (in none of them so far is doing this superior to a .50 cent 555) but not with just those two components as a general replacement for a 555. I have no idea what he was talking about. If that worked I don't think a 555 would be as popular as it is. Now, certainly there's a time to near full charge of a capacitor which will vary depending on construction of the capacitor, circuit resistance and environmental conditions and fiddling with that delay does have some applications, but if this circuit exists I don't understand why I've never seen an example of it and can't find a schematic for it in the decades since when I've gotten curious again and tried to look it up. I also don't understand how it could work because both resistors and capacitors behave stably with a straight DC source and no other load. Yeah, you get some resonant stuff going on at higher frequencies when the circuit is part of something else, or just when you hit it with a high frequency input signal because you wonder if maybe that fellow thought I was supply my DC motor (the thing I wanted to time when I asked him that question back in about 1992) with a magical 9v battery that put out a 1mhz+ signal for some odd reason, which doesn't, in the case of my DC hobby motor, work. I'd predict it wouldn't because hysterisis exists and feeding a DC motor an AC signal isn't going to make the motor turn enough in either direction to matter, but I had to try. Why I can hear the weird noises it makes when connected to a 1mhz signal I don't understand, but that test made the world's least efficient high frequency buzzer.

From a 9v battery with nothing but a R & C (what he said) in the circuit I can't see this producing a stable frequency, other than in so far as 0hz is technically both a frequency and stable. A couple of times I've tried building random value RC circuits and tested the circuit in case I fundamentally misunderstood something about electronics, I see the cap charging on initial connection and then the circuit is stable and does nothing. Which is what I would predict based on everything I know, but it has always bothered me that maybe I missed something or misunderstood what he meant.

Does anyone know what he might have been talking about? Maybe this was used for something back before the transistor days, pretty sure he went to college in the days of vacuum tubes. If this exists, do you know where can I find a schematic to build and test this? Is it just bad luck I've not seen this used anywhere before or are there some draw backs to it aside from the one I ran into (RC timing on a battery changes with discharge in absence of voltage regulator and low voltage cut off, and if you do use those then you kill your circuit way sooner than needed)?

Thank you very much for your time.

 

Well, the short answer is no.

 

Well, the short answer is no.

That's what I thought. Thanks, with that confirmation I can ponder more interesting questions.

 

This isn't a homework question, but it is educational and fits better here than in the Education category. Decades ago, before the internet, I lived in rural Alaska and there was this older fellow who sometimes built circuits that sometimes worked. He was the only person within about 100 miles of air travel (there were no roads) who knew anything about electronics. I wanted a timer for a DC motor driven off a battery and he told me that you could connect a resistor and capacitor to a DC source (a 9v battery I believe he said) and somehow get behavior similar to a stripped down 555 out of it.

Years later I know a bit more than I did as a kid. I'm not an EE, but I build circuits on a regular basis. I can make this work by adding other things in specific applications, (in none of them so far is doing this superior to a .50 cent 555) but not with just those two components as a general replacement for a 555. I have no idea what he was talking about. If that worked I don't think a 555 would be as popular as it is. Now, certainly there's a time to near full charge of a capacitor which will vary depending on construction of the capacitor, circuit resistance and environmental conditions and fiddling with that delay does have some applications, but if this circuit exists I don't understand why I've never seen an example of it and can't find a schematic for it in the decades since when I've gotten curious again and tried to look it up. I also don't understand how it could work because both resistors and capacitors behave stably with a straight DC source and no other load. Yeah, you get some resonant stuff going on at higher frequencies when the circuit is part of something else, or just when you hit it with a high frequency input signal because you wonder if maybe that fellow thought I was supply my DC motor (the thing I wanted to time when I asked him that question back in about 1992) with a magical 9v battery that put out a 1mhz+ signal for some odd reason, which doesn't, in the case of my DC hobby motor, work. I'd predict it wouldn't because hysterisis exists and feeding a DC motor an AC signal isn't going to make the motor turn enough in either direction to matter, but I had to try. Why I can hear the weird noises it makes when connected to a 1mhz signal I don't understand, but that test made the world's least efficient high frequency buzzer.

From a 9v battery with nothing but a R & C (what he said) in the circuit I can't see this producing a stable frequency, other than in so far as 0hz is technically both a frequency and stable. A couple of times I've tried building random value RC circuits and tested the circuit in case I fundamentally misunderstood something about electronics, I see the cap charging on initial connection and then the circuit is stable and does nothing. Which is what I would predict based on everything I know, but it has always bothered me that maybe I missed something or misunderstood what he meant.

Does anyone know what he might have been talking about? Maybe this was used for something back before the transistor days, pretty sure he went to college in the days of vacuum tubes. If this exists, do you know where can I find a schematic to build and test this? Is it just bad luck I've not seen this used anywhere before or are there some draw backs to it aside from the one I ran into (RC timing on a battery changes with discharge in absence of voltage regulator and low voltage cut off, and if you do use those then you kill your circuit way sooner than needed)?

Thank you very much for your time.

Hi,

Yes, there is no way to build an oscillator with just a 9v battery, a single resistor, and a single capacitor. The response will always be overdamped which means it will never oscillate.

There are various ways you might change the circuit a little and if you have unusual circumstances, you might see an oscillation, but oscillators are usually built on principles that are known to produce repeated oscillations for as long as you want them to continue.

There is one interesting exception, but it is in theory only, meaning it would be very hard to build one. That is a 9v battery, a resistor, a capacitor, and an inductor. Well actually, just a 9v battery and a capacitor and an inductor, with no resistor.
In theory, if you energize an ideal inductor and ideal capacitor (in parallel) with a power source like a 9v battery, then remove the power, the capacitor and inductor will oscillate indefinitely. This is highly theoretical though, and although in theory this is correct there is probably no way to build a real life oscillator like this because even the smallest resistance (always part of each component) the energy will diminish over time and the oscillations will cease.
It is interesting that this works in theory though even though not in real life with real components. It's also a little interesting that even in theory you could never measure the oscillations unless you use a zero-energy measurement method which would also be in theory only.

 

Hi,

Yes, there is no way to build an oscillator with just a 9v battery, a single resistor, and a single capacitor. The response will always be overdamped which means it will never oscillate.

There are various ways you might change the circuit a little and if you have unusual circumstances, you might see an oscillation, but oscillators are usually built on principles that are known to produce repeated oscillations for as long as you want them to continue.

There is one interesting exception, but it is in theory only, meaning it would be very hard to build one. That is a 9v battery, a resistor, a capacitor, and an inductor. Well actually, just a 9v battery and a capacitor and an inductor, with no resistor.
In theory, if you energize an ideal inductor and ideal capacitor (in parallel) with a power source like a 9v battery, then remove the power, the capacitor and inductor will oscillate indefinitely. This is highly theoretical though, and although in theory this is correct there is probably no way to build a real life oscillator like this because even the smallest resistance (always part of each component) the energy will diminish over time and the oscillations will cease.
It is interesting that this works in theory though even though not in real life with real components. It's also a little interesting that even in theory you could never measure the oscillations unless you use a zero-energy measurement method which would also be in theory only.

This is very interesting, thank you very much for taking the time to write it up. I didn't know that those components could behave that way in theory. As always, I have more to learn. Also, love your choice in avatars.

 

Hi,

Yes, there is no way to build an oscillator with just a 9v battery, a single resistor, and a single capacitor. The response will always be overdamped which means it will never oscillate.

There are various ways you might change the circuit a little and if you have unusual circumstances, you might see an oscillation, but oscillators are usually built on principles that are known to produce repeated oscillations for as long as you want them to continue.

There is one interesting exception, but it is in theory only, meaning it would be very hard to build one. That is a 9v battery, a resistor, a capacitor, and an inductor. Well actually, just a 9v battery and a capacitor and an inductor, with no resistor.
In theory, if you energize an ideal inductor and ideal capacitor (in parallel) with a power source like a 9v battery, then remove the power, the capacitor and inductor will oscillate indefinitely. This is highly theoretical though, and although in theory this is correct there is probably no way to build a real life oscillator like this because even the smallest resistance (always part of each component) the energy will diminish over time and the oscillations will cease.
It is interesting that this works in theory though even though not in real life with real components. It's also a little interesting that even in theory you could never measure the oscillations unless you use a zero-energy measurement method which would also be in theory only.

No, it does not work in theory even with ideal components. It would radiate EM waves and lose energy.

 

You could get the RLC/RC circuit and a battery (energy source) to oscillate if some part of R ( like a galvanized metal strip) has negative resistance.

http://www.sparkbangbuzz.com/els/zincosc-el.htm

https://commons.wikimedia.org/wiki/File:Crystodyne_zincite_oscillator_-_top.png

 

Just go to mouser or digikey and order some -100Ω resistors.

 

No, it does not work in theory even with ideal components. It would radiate EM waves and lose energy.

Just go to mouser or digikey and order some -100Ω resistors.

I'm going to go out on a limb here and guess that you're not a big fan of theory.

A friend of mine claims that tequila causes her internal resistance to go negative, so I guess the only real issue is translating that effect to electronic circuits.

 

Just go to mouser or digikey and order some -100Ω resistors.

https://www.electronics-notes.com/articles/electronic_components/diode/gunn-microwave-diode.php

The Gunn diode operation depends on the fact that it has a voltage controlled negative resistance – this being dependent upon the fact that when a voltage is placed across the device, most of the voltage appears across the inner active region. This inner region is particularly thin and this means that the voltage gradient that exists in this region is exceedingly high.

https://www.mouser.com/c/?q=gunn diode

Gunn Diode Characteristics

It's pretty easy to make one by heating a galvanized metal strip or just buy a zincite crystal sample. Today, a person would use the semiconductor negative resistance device version like TEK did for high speed switching on the older scopes.
https://w140.com/tekwiki/wiki/Tunnel_diodes



https://commons.wikimedia.org/wiki/File:Krystadyna_charakterystyka_prądowo-napięciowa.svg
https://earlyradiohistory.us/1924cry.htm

There seems to be a myth (a default assumption of circuit theory of ideal components) that resistance is almost always ohmic. In fact, most electrical resistance in nature is decidedly non-ohmic and often has what we classify as negative resistance curves.

 

@nsaspook, I know what negative resistance is. My comment was based on the fact that the TS is seeking a circuit with a battery, resistor and capacitor that oscillates. Devices having negative resistance are not resistors, therefore it is not a solution to his request.

 

@nsaspook, I know what negative resistance is. My comment was based on the fact that the TS is seeking a circuit with a battery, resistor and capacitor that oscillates. Devices having negative resistance are not resistors, therefore it is not a solution to his request.

I would disagree with the metal based NR devices (100 year old devices that predate semiconductors) that are not manufactured as semiconductor devices (with much more reliable and predictable NR curves than the old devices). They are resistors (an electrical component that limits or regulates the flow of electrical current) just like ceramics composites, plastics, and other metal type resistors are and are operated in the positive voltage and current quadrant as a resistive component.

Negative resistance (negative differential resistance) is a characteristic of the device that can be passive or active.

 

@nsaspook, I know what negative resistance is. My comment was based on the fact that the TS is seeking a circuit with a battery, resistor and capacitor that oscillates. Devices having negative resistance are not resistors, therefore it is not a solution to his request.

You're not wrong, still, I'm learning a lot from this disagreement so I have no complaints. Also, respect to both of you for disagreeing and staying civil. To be clear, I have no idea what most of what both of you are saying means but looking it up has taught me the shape of a disagreement I didn't realize existed.

The actual solution ten year old me employed was getting a L293D, 555 and other bog standard components and running my motor. Good to have confirmation that I didn't just chicken out of solving a "simple" RC oscillating circuit.

 

No, it does not work in theory even with ideal components. It would radiate EM waves and lose energy.

Hi,

Theory is as theory does, so sayeth the whole premise of what theory really is.

The way theory works is there is always some assumptions that are strictly followed. This means that your assumptions may not be the same as mine for a given theoretical problem.

In this case, it is known that, or at least said that, in theory an LC parallel combination would oscillate forever. This is not a new statement either, it comes from long ago. How is this possible with at least some radiation? The answer is very simple, just like everything else in theory, we have to set up the platform by which we can dictate what is going to happen. The platform here is not only past quotes exactly like this, but that we simply, very simply, IGNORE the more subtle metrics that are always present in REAL LIFE. We do that by specifying "ideal components".

So what is an "ideal component". It's usually a component that has no losses for one thing, and that basically includes everything that can cause a loss of energy.

There's also the context though. If someone says in theory that there are no losses, then there are no losses, period. It doesn't matter if there is, in real life, radiation or resistance or one of Santa Clause's merry elves decides to tap off some energy to help build better toys in the workshop (ha ha).

So, what you say is true, but it is also true that there are no losses so the LC circuit would oscillate forever. If we change the assumptions then your statement is certainly true, but you have to realize this is a well-known way of explaining an ideal LC circuit that has been energized at least once in its lifetime.

Here are a few other statements we can use to contrast the different ways of looking at this.
1. An LC circuit will oscillate forever given some initial energy.
2. An LC circuit could oscillate forever given some initial energy.
3. An LC circuit will not oscillate forever even given some large initial energy.

All these statements are true when taken under the proper context.

 

This is very interesting, thank you very much for taking the time to write it up. I didn't know that those components could behave that way in theory. As always, I have more to learn. Also, love your choice in avatars.

Hi,

Oh, you are welcome for sure. BTW, do you recognize that character? Ha ha, I modified it slightly.

 

You're not wrong, still, I'm learning a lot from this disagreement so I have no complaints. Also, respect to both of you for disagreeing and staying civil. To be clear, I have no idea what most of what both of you are saying means but looking it up has taught me the shape of a disagreement I didn't realize existed.

The actual solution ten year old me employed was getting a L293D, 555 and other bog standard components and running my motor. Good to have confirmation that I didn't just chicken out of solving a "simple" RC oscillating circuit.

There's not much of a disagreement really. Only a discussion of resistance as a electrical property R (as in RLC used to design and predict circuit operation) vs the modern definition of a resistor as a physical component. IMO, R as a electrical property is the proper usage with NR oscillating circuit theory that can include something as simple as a neon bulb RC oscillating circuit. It's the same as using a varactor for C in the circuit for tuning the frequency.

 

Hi,

Oh, you are welcome for sure. BTW, do you recognize that character? Ha ha, I modified it slightly.

Well, of course! Who wouldn't recognize God?

I think God might have a bit more hair scruffle up top in your version, had to pull up one of the original sceencaps to compare it to.

 

Theory is as theory does, so sayeth the whole premise of what theory really is.

Maxwell’s equations are pretty well established. A varying electric or magnetic field radiates EM waves. Nothing you have to say about it is if any consequence.

 

Maxwell’s equations are pretty well established. A varying electric or magnetic field radiates EM waves. Nothing you have to say about it is if any consequence.

Hi,

That's a pretty nutty statement you obviously do not understand how theory works.
From now on, if you post a circuit with a resistor in it, I am going to show how it can't be right unless you show how the quantum effects change the behavior of each and every resistor, and how the placement on the PC board effects the field interactions of each and every part on the board, and any parts on any other boards in the same room, or even in the same universe. See it's easy to get pedantic about things taken out of context.

The only difference is what level of theory you go down to. Even Spice has ways to handle this.
What else you might be suggesting is that every time we show a circuit, we have to spell out a complete disclaimer for what we elected not to show. Most people here I would bet can tell by the context.

I will say that it is not a bad idea to mention other effects, but to do so with such a way of saying it "Nothing you can say..." is rather strange. You don't know what someone else can say until they say it.

 

Well, of course! Who wouldn't recognize God?

I think God might have a bit more hair scruffle up top in your version, had to pull up one of the original sceencaps to compare it to.

Hi,

Oh, well then i know what you watch on TV (ha ha).
Yes it is the God of South Park, a really funny version too
I modified it to avoid any issues with copyrights, but then again i am sure the Fair Use Act would cover it anyway and the South Park team gets a little free advertisement out of it.