Classic Circuits You Should Know: Astable Multivibrator
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- เผยแพร่เมื่อ 10 ก.พ. 2019
- Classic Circuits You Should Know: Astable Multivibrator
HEY YOU ABOUT TO POST SOMETHING STUPID:
Yes, I know my hands are large/fat. It's because of a heart condition I suffer from called Congestive Heart Failure. Here's a link to some information about CHF: cle.clinic/2TdS2Ux
One of the symptoms is that is causes fluid retention, mostly in the hands, feet/ankles, and face.
It will kill me one day. I'm doing ok right now, but someday...
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"Only reason it works is cause nothing is perfect..." A Definition of the Universe..!!
Underrated Comment.
Well, actually, the conditions for the universe have to be PERFECT for stars etc to form.
Its these basics in electronics that are so hard to find clearly explained, thank you for sharing your skills.👍👍👍
Just ❤ these vids.
Very popular circuit design. I remember soldering together the siren kit from Elenco (SP-1A), with added caps, 555 timer, pot and 8 ohm speaker. Fun soldering practice for beginners.
every time you explain things like this, I gain a bit more understanding, so thanks for posting these rather simple circuits that can be used to explain bigger concepts.
why didn't I know this before I used 555's everywhere. THANK you so much for showing me this
Teacher: Did you understand this lesson today?
Me: I don’t understand everything
You know someone's engineering skills are solid when they misspell simple words 😂
Every good engineer I know is a horrible speller haha
For the same reason that doctors have the absolute worst handwriting. I have no idea how the pharmacist could understand some of the scripts the doctor wrote back in the day before it was all computerised, but they seemed to be able to figure it out.
Oh, the reason? Handwriting is a right brain activity, while being a doctor is left brain (analytical). Yes that's an oversimplification of the issue because brains are complicated but it's pretty interesting how it holds true.
The videos has been helping me loosen up some frustration trying to put circuits to work fine. Because I now understand stuffs better.
Thank you for not allowing your large hand stop you from making videos to help us!
Thank you, everything in this video was so well-explained and very clear. I loved the walkthrough as you drew the schematic. Subscribed!
These are my favorite of your vids, explanations are spot on, and easy for the newbie to comprehend.
Thank you
you're the BEST!! I just started a hobby project of mine to make electrical stuff and i spent half an hour looking for videos and i saw your video and you are the only one who has a good explanation! (You should show how you connected the bits in the breadboard)
THANK YOU!!
I soldered one of these circuits together in Dolan Hall at Kessler AFB in 1988. Thank you for your videos. I enjoy them very much.
Thank you kindly for all your informative videos, they have been a tremendous source of great information and pleasure for me. They have brought me many joyful evening playing with breadboards. I wish you all the best!
Love this easy simple circuits
Thank you Paul
Have a nice day and take care
Thank you, very interesting and informative. You design your videos on the assumption that people are at the very beginnig of electronics, this is whats so good about them, they assume nothing. Excellent, thank you again.
As an old journeyman certified technician, your videos are a good refresher.
I just love these videos, Paul!
Thank you and much love to you!
Man, thank you for this video, you made my day! I have learned this circuit from my grandpa 30 years ago. I will build one again.
This is a great video. It explains a lot in a way that makes it totally easy to understand.
Thanks for making this simply easier to understand! Thanks for your help!
Another good 'un Paul for guys/girls still feeling the way around these back to basics circuits are helping to build foundations. I add them to a small note book once Ive got it working and played about with it so keep 'em coming I want to fill a few of them up!
I remember buying the parts from radioshack and twisting this together myself when I was 13. Thanks for the awesome video.
This was my first ever circuit I've built... and the PCB was etched in HNO3 after I've draw it with nail polish... somewhere around 1980... Behind the iron curtain it's obvious it was made with no LED's but bulb lights and with Ge transistors... :P
I really appreciate the in-depth video describing how it works. It really bothers me that there aren't to many good quality videos and like yours. Subscribed!
I actually also really enjoy watching it too compared to other videos
Thank you very much
Nice demonstration on the classic astable multivibrator. That circuit works even better if you connect the capacitors between the diodes and the collector. What you are forming is a differentiator with R3/C2 so that when the voltage at the collector of the rightmost BJT goes low, the negative transition is coupled to the leftmost BJT base. Therefore, the leftmost BJT stops conduction.
By placing the capacitor on the anode side of the LED, you are left with a lower valued negative pulse - it works, but may not through temperature ranges. As R3/C2 charge, the left BJT stays off and the right BJT stays on. This continues until Vbe on the leftmost BJT reaches 0.6V to turn it on.
When it comes on, it comes on hard and pulls C1 towards ground (but the LED conduction of 1.8V + Vce(sat) of 0.4V keeps it from hitting 0V). R2/C1 form a differentiator; so the negative pulse pulls through to the base of the rightmost BJT - forcing the charge out of the base and turning it off. The cycle continues ad infinitum.
If you placed your scope at the collector of the BJT, you would have had an easier capture, as the pulse pulls withing Vce(sat) of ground, Where you had it was pulling Vce(sat) + about 2V for a green LED (1.7V for red).
You are spot on as to why this circuit starts up as it does! It is a race between the BJT's, Rs and Cs as to who gets to turn-on first. Since nothing is perfect, one of them wins the race!
@learnelectronics, you should do a monostable multivibrator, too! I think that'd be cool. We'd learn about AC coupling and differentiators and how a small pulse can turn on (and keep on) a BJT using that trick.
i absolutely loved this video thank you for uploading this
Thanks. Nice explanation. For years in teaching I have found it a challenge to talk and write correctly simultaneously, so no apology!
Thank you very much
Best circuit teacher I found! Thanks so much for these great vids :)
thank you enjoyed watching the video very much.
it seems as though no one else, even some people who have websites you pay to join can not explain this. so thank you very, very much
Really good videos. Much appreciated.
Well explained
Really excited about the upcoming videos
Love it
Thanks for sharing your knowledge.
Thanks bro. I’m gonna try this. Cool.👍👍
Thank you so much for your tutorial sir
Thank you for posting
Neat little tricks. Electronic McGyver is how I feel like many of these modern circuits came about XP
Thanks for the video. First you say that the manufacturing tolerances are the reason why the LED's are oscillating, but later on you say that that's the reason why one LED blinks on first. I think only the latter is true. The oscillation happens because of one side of a capacitor dropping the voltage when a transistor opens, and then charging up again.
Thanks for the video, i learned something!
great work .try varying the resistances and capacitances for varying oscilation speed
Great Video and it looks like I will definitely be getting back..
Great Circuit, that's like the Railway Crossing Lights ;)
that is so cool. its like a perfect imperfection
Really cool vid. Id love to see a quick build of the astable multivibe breadboard
Love this video, seen the same circuit on a toy years ago and I was amazed by it, you have expended it very well, keep up the great work 👍
Amazing video Thank you!!!!
I'ma just comment and say thank you for videos like this
Thanks this has helped me (I think/hope) to understand another video where someone did something similar but used LDRs. In that case the frequency pulsated - alas there was no explanation of the circuit though.
Waiting for the train to pass, bit the blinking lights keep going on and off.
Paul, thanks for the video and putting up with my bad jokes.
Because the Base or Gate is like a capacitor, it takes time to charge up to the 0.6v depending on the resistor you provide.
Learned this circuit from my radio shack 10-in-1 circuit kit. Never could figure out why it worked and the book didn't explain it except in the most basic sense.
Good 'ol RC circuits. Neat concept to show tolerances. I believe you had a video on oscillating two LED's like this with an NPN and PNP transistor. Similar effect for a completely different reason.
roger roger
I've done basically this circuit with 555 timers. Setting it done without ICs is pretty cool
Nice explanation Sir!
Great topic series. There was a large library size dictionary book of circuit examples (80's) vintage that I really enjoyed. Anyone know the title? (My assumption is that it would be a common book amongst students/designers)
If I can ask what is a good brand of transistor to purchase. Going to purchase a assorted pack just need to know a good name brand. Thanks for any info Artie 👍 also the blue small resistors are they 1/8 watt
The two resistor are controlling the charge of the condenser but the quirkiness is that in your first example explanation following the 1k resistor that would charge one side of the condenser but this would cause a polarity potential difference between those two points, I mean obviously either end of the condenser then that equalization causes the rise to the gate potential, so I think it is tolerance differences but mostly the key is the condenser disequilibrium. No?
Basic circuit to test components in a oscillation manner. also the capacitors have their tolerances.
Larger resistor should increase the time of charging the capacitors hence frequency ought to decrease. Am I correct?
Our class made one of these up in 1974 to demonstrate capacity, we used neon bulbs back the and after it was built we put it on a shelf powered by a battery and took bets on how long it would run . I think it ran for about 6 weeks non stop.
Very Cool!
Great video Paul.
My internet is going to be off for the next few weeks but I just wanted you to know I will catching up on videos when I can afford my internet again.
Thanks for all you do man.
I'll be here.
Remember that there are many places like restaurants, libraries, rest areas and many truck stops that will have FREE WI-FI. Just FYI. KR222.
Excellent. Plz van you help me? I need To make a same circuit with short time ON (10000 miliseconds) and a long time OFF (2hours). What can ranges of capacitors and résistances?
Initially the capacitors have the the same voltage across them So they can not charge. Both the bases have a bias from the 47k but due to the dopping differences of the transistor junctions, one will turn on first hence the first quick flash. It’s not the capacitors or value of the resistors they determine the frequency and Mak space ratio.
I tried pretty hard to figure our why it was oscillating at the question portion and drew a blank. Tolerances (i.e. real world) I did not think of (stuck on theoretical). Thanks for these mental exercises as LRC does take me some time to figure out and I am learning from your videos.
I was thinking a current mirror coming from the astable multivibrator would compress the solar kinteic current into a power form it it starts with a bridge refticer that's loaded back backwards into it's power loads would that stabilize my compression power I'm making from light
Outstanding explanation. I wonder whether there are any books with classic circuits
Thanks for the explanation. I have a dumb question (I think).. at 4:30 you say that the capacitor on the right charges up enough to turn on the transistor on the left. Why does it need the capacitor to do this? Isn't its base also connected directly to Vcc via R3, like ALL the time? So it should NEVER turn off, right?
the slight change in the actual values of the resistors must affect the blinking or oscillation of LEDs continuously like the right LED showed in the beginning but they seem to oscillate at a regular interval why and how?
"What's happening guys?" Looks like 2 green LED's are flashing! 🤣
Hi...what changes would be required to run it off 48VDC 100mA ... Thank you
i remember we learned this in 5th form electronics when i didn't follow and had trouble learning & stuff. i remember this circuit but had no freaking clue how it worked. i remember the teacher saying it started blinking cos the components werent perfect but thats all i remembered. its cool to know what it actually was now that im old and getting into electronics and can sorta get it now. i dont fully get it of course, but i will when i build it & put my scope on it. good video man cheers. please make love to lots of beautiful women and spread your genes & improve the human race
As always nice video.
I used to kinda get this one but looking at it now I still dont get where the charge goes on the transistor side of each capacitor, surely the cap cant charge if it doesn't have both sides connected ? I know transistor has a tiny bit of current flow through its gate but is it enough to charge up the capacitor ? also I don't get the purpose of the 10k resistor
Can you please show the calculations behind your chosen values? I'm just a beginner and my knowledge is pretty limited. I really want to know how you arrived at these values and how we can tweak them around as per our will.
The moment you said the name of it, my gf became very intresting in what I'm seeing but then she looked so disappointed LoL
Nice video, but what is the use of resistor R2 and R3 in the circuit if only R1 and R4 are used for charging
very cool circuit
can you post a circuit diagram image or something it would really help... Thanks!
Nice video. Cheers
I have a number of beginner electronics books and they all use bipolar transistors in the astable multivibrator build. So I looked up youtube videos about the same topic and they all use bipolar transistors. So why does everyone use them? Why not use mosfets or I.G.B.T.s or is there a reason why they are never used?
Was/is there a reason for using a Tantalum rather than an electrolytic?
I made the same circuit and it works for me but when I plug it in both of the leds light up and I have to short the resistors with my finger to make it work
OH now do I understand!! :-)
I did for some time ago look at a schematic of an astable multivibrator but could for the life of me not see the logic in how that should work, no matter how I did look at it were there no logical explanation on how that should start blinking! But electronic is fun and investigation could only add to the fun, so I did thought, I'd just draw the circuit in an visual simulator and then I know what's going on. But to my surprise did both diodes just glow and nothing else happened. I did redraw the circuit several times but every time with same result. :-)
Good interesting video. I have looked at a lot of these videos, and many others include blatant errors that will destroy your LED's, or they don't give you component values, etc. I would have liked to have seen alternative values for the base resistors that would show different speeds, and a non-symetrical duty cycle. That would have been interesting. Thanks.
You might be interested in my lasted post about this circuit
hey both flashed... or was that just my mind that did that... I do get some activity in there from time to time.. ooo this is sooo cool...
Thanks
Ill give thumbs up for the transformer icon at 5:43 😀
Nice closup
Rail Rod crossing flasher. Great job. Really like these. But write bigger.
So when I turn on power to the circuit the leds are just on, but when I reconnect stuff it stars blinking. What's causing it to not immediately blink?
Something I do is add a tiny speaker in place of the led when it switches really fast to hear the ear can hear faster then the eye can see in terms of frequency
Great idea!
What happens when two resistors are matched? Would be better to swap out for two 500k pots wouldn't it?
Is it possible to daisy chain 2 astable multivibrators and get 4 cycling states?
For some reason I think the frequency is determined by the value of the capacitor and the duty cycle is determined by the value of R.
Large R1 compare to R2 give you longer on time (pulse width) and less off time ( space width). If you swap them R values ( swap R2 and R1 and the same with R4 and R3, you will end up with long on time and less off time while your frequency remains the same. Right?
If I want to see what the value of C must be to get 60Hz
F= 1.44/ [ R1+2(R2)] x C.
C=1.44/[R1+2(R2)]xF
Most likely they are all tied up with each other from the looks of it all.
Did I miss something?
What’s the frequency, Kenneth?
Nice video, like your all videos. I appreciate all of this but would be pretty grateful if you can clarify how are the capacitors being carged when they are connected from their both sides to the positive rail of the power supply, so there is bassically no potential difference to charge them.
All I can guess is that due to the different voltages, any current flow will flow more slowly through one resistor than the other creating some kind of pseudo-capacitance, like a high flow rate water pipe connected by a perpendicular pipe to a low flow pipe resulting in a pressure (voltage) difference.
Hello, thank you for your video. Question please, why does this still work if the inside of the circuit capacitor is positive or negative? I thought capacitor needs to be positive to discharge? thank you
Capacitors discharge when they are no longer charging. So in DC operation when there is no longer a current at the anode, the charge accumulated in the cathode basically just runs out. Things are much different in AC operation.
I am hooked to this channel, watching all your videos from the beginning one by one. I read you teach at a college, do you record your lectures too? Would love to watch them.
I am retired. But thank you.
Why You not examining the 1K resistors, they also not equal and not perfect ?
And I think if we let the circuit run for long time there will be a moment in which the two led will lights at the same time. The chaos low :)
I build the circuit and it's blink only when I use electrolytic capacitors instead of ceramic ?!
Great video and explanation! What about the tolerance of the capacitors? Could they play a role as well? I love the conclusioni: "It works because nothing is perfect" ;)
To a small amount the capacitor tolerance plays a roll, but its very very tiny. The resistors control the speed at which the caps charge.