Fail design attempt.

I used 22uf for the caps and 1k for the resistors, the transistors are little bc548 npn's.

So I'm trying a resistor capacitor + transistor oscillator it didnt work.

It supposed to use the capacitor chain to delay the power till it reaches the end, and when it reaches the end, its supposed to fire the bases of the transistors and cause the capacitors to discharge through a short.

But what happened was, it seemed to have a delay, but im not sure if the collector and emitter were connecting, or they werent, its either too much current and the bases are firing too early before its reached the top properly, or not enough hitting the bases at all, its hard for me to say what it is.

The capacitors are all getting a good voltage, just shy off the power supply, so I'm not sure what it is, it seemed to sometimes flicker a little bit and bob up and down, but it didnt develop a stable oscillation, apart from just some little hiccups which im not sure were just dodgy connections or not.

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I expect this circuit will not oscillate. It will reach a steady state where the LED current to the transistor base(s) is just sufficient to stop the LED current increasing.

I see only negative feedback and no hysteresis.

 

Thanks for the feedback. I tried getting rid of the top transistor, so the last cap naturally discharges by itself through the rest of the bases, which it should be able to do, because there is a second free loop for it, I lost alot of volts on the caps having the extra loop, the delay still seems to be there, so I think.

Maybe its taking too long to discharge out of the top cap?? I tried dropping the farads didnt make much of a dif.

 

What leads you to believe that circuit can or will oscillate. I am dubious about your ability to show the necessary condition for oscillation since you do not appear to think that component values are relevant. Just because you can meet the necessary condition still does not mean your circuit will oscillate.

 

http://imgur.com/4D85Bty

Heres the modification. I swear I saw it working... but then it stopped afterwards...

I have reason to believe this circuit can oscillate, and I have made sure the component values were taking into account.

It does seem to be hitting a steady state, unfortunately.

But when I put the volts up to past 10 volts, the led at the top fades away. and I cant think of any reason this would happen?!?!?
the voltage on the last cap is going DOWN, when I put the supply UP, that doesnt make sense!!!!

I think maybe its a beginners transistor mistake??? Ill definitely keep looking at it.
With my "radios" (which I mean just hooking up a little transistor directly to a speaker.) sometimes the loudness goes down as well, after its been going for a while - what would cause that to happen? It may be happening on this oscillator!

 

Look up "phase shift oscillator", which is probably what you are trying to design.
I wonder if perhaps you circuit might work with a diac instead of your LED.

 

Thanks Ian, yeh instead of diving right into the deep end of design when I know bugger all, I could use someone elses just get something running to begin with...

But Ive got another idea for it the same-> Maybe I have to time the top capacitor discharging, with the rest of the caps discharging, so they all discharge at the same rate? If The lower caps discharge quicker itll leave constant charge on the top, maybe they have all discharge at the same rate!

 

I wonder if perhaps you circuit might work with a diac instead of your LED.

With a diac you can make an oscillator with the addition of one rsistor and one capacitor but it would need a supply of more than 30V.

 

Ill look up a diac, thanks... is that bodgable just with 2 ordinary diodes back to back?

But Adding the 1ohm resistors to the transistor pathways to discharge the caps all unanimously speeded as the top cap empties with the same ohmage didnt come through with anything.

 

is that bodgable just with 2 ordinary diodes back to back?

No, that won't work.

 

I have reason to believe this circuit can oscillate, and I have made sure the component values were taking into account.

We prefer for the flow in schematics to be primarily left to right and top to bottom. You have yours drawn in a way that makes it difficult to read.

I don't see an oscillator.

That's easier to see in this schematic:

 

haha thanks alot for that beautiful printed one of my circuit, I feel the love. I think u've translated it correctly, from a short inspection.
I saved the image thanx.
I cant believe you put so much time into a circuit that doesnt even work. hehe

Its nice but I prefer the all loops defined to only isolated grounds being separate gnd icons, rather than the separate ground exit points for a single asterix/star point method, but I know both are valid to read, depends on what ur used to.

I just actually did another 2 hours work on another design I'm positive is correct, and its not working, I'm not really worried tho, for spooky reasons some things just dont eventuate.

This oscillator actually started off as a marx generator embellished with transistors, tried to turn it into an oscillator, didnt work, don't really care it didn't sometimes not meant to be.

 

Its nice but I prefer the all loops defined to only isolated grounds being separate gnd icons, rather than the separate ground exit points for a single asterix/star point method, but I know both are valid to read, depends on what ur used to.

I chose to not connect the grounds for readability. Similarly, I thought about putting the voltage divider on the left (where it would normally be drawn), but I didn't want the extra wire crossings. Neatly drawn schematics are easier to read, and that's the usual goal; easier to read, easier to understand.

I didn't remember that you said you were using 22uF capacitors (doesn't make a significant difference) or that you were using BC548 transistors (not significant either). Most prefer to have the component values written on the schematic, and component designators should be used when more than one of each type is used. Most schematic editors add them automatically, so you'll usually see designators even when there's only one of each type.

 

voltage divider? (yes, i know it was reducting the volts, but it was still acceptable, but i cant see the voltage divider myself.)

Yeh and thats why it does need a good 20v to run, because of the voltage loss down the ladder. funny.
Its good that u can see it, quite impressive from my fellow man there. I often am a little disbelieving in my brothers, but I'm learning a lesson there... every day...

 

Your circuit reminds me of a ring oscillator with the parts re-arranged

have you seen this: https://en.m.wikipedia.org/wiki/Ring_oscillator

It is one of the few circuits that always oscillates.

 

I actually have a ring oscillator as well, it seemed to go + - +, then - + -, then + - +, introducing power at each stage, (it made the inversion pattern in front of it. but alas... it also didnt oscillate when i went to go run it.

Funny, so close, no cigaret.

I actually did it with 3 separate batteries, 1 on each unit. it was kinda cool, maybe ill attempt it again some day.

 

I actually have a ring oscillator as well, it seemed to go + - +, then - + -, then + - +, introducing power at each stage, (it made the inversion pattern in front of it. but alas... it also didnt oscillate when i went to go run it.

You mean something like this?

 

that looks cool - does it work? Or did u just make it up then?
On a short inspection I say it doesnt work, the capacitor fills, activates the disharge the next cap, but it will never ever stop discharging, and never charge again. am I right?

definitely has the cool look to it tho, a bit like all my circuits.

 

I used to just that circuit when I needed clock sourced back in the 1960's (the only logic gates available at that timer were RTL, and they were expensive).

 

Heres another one of my fails, when one side charges its supposed to open a short on the other side, to discharge the opponent capacitor, but for some reason, no worky, no idea.