How a 2 transistor LED flasher circuit oscillator works | Easy simple explanation
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- เผยแพร่เมื่อ 13 พ.ค. 2024
- Explanatory video where I explain exactly how the 2 transistor BJT LED flasher oscillator circuit works. Also called an astable multivibrator or transistor oscillator. 2 BC547 transistors, 2 capacitors and 4 resistors is all it takes.
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My daughter brought this circuit home from school but didn't have a clue how it worked. And with my elementary electronics, I sort of figured out what was happening but this explanation really got the LEDs of my brain lit! I'm subscribing hoping to further my knowledge of elementary electronics. BIG THUMBS UP!!
After browsing tons of video, this is the clearest explanation, especially with the relative negative voltage across the capacitor every-time each transistor becomes closed. Thank you
This was the BEST explanation of a flip flop oscillator I've ever listened to. Seriously you have no idea how many times I have heard this in ways where they don't explain things well, like why does the voltage turn negative. It makes so much sense when you broke it down. I'm an electrician and love electronics. This circuit was always a huge road block for me. It doesn't seem like a useful circuit in sensitive electronics. Maybe for a simple blinking circuit. Where do they use this circuit in? I hope you make more videos like this!
Thank you! I really appreciate your feedback. I'm happy it helped you understand. The circuit itself is mainly used for non critical circuits like light effects or as a simple oscillator where the frequency doesn't have to be very stable. But like always with electronics, your imagination is the only limit. Circuits can always be modified for different purposes.
Amazing explanation! Not just how you do, but how it works. Thank you
It’s the clearest illustration I’ve watched as a layman. The numbers really help me to understand. Thank you!
The best explanation for this circuit thanks ❤❤❤
I remembered when I was in high school, my first project was to build this LED blinker. Watching this video helped me to understand why and how it worked.
You finally make it make sense. It's been years since I've taken electronics, and I'm sorry to my teacher. But you explained the "resistor capacitor pair" and explaining the -11.3v bit and it clicked. Thank you!
At last someone who realy know how to explain in the simpliest and precise way electronics, I've looked
at least 10 videos on TH-cam, and at the end of each one I was more confused. GlevoTec Well Done!!
Thank you! I really appreciate that. I'm glad you found my video helpful.
Thank you very much sir I was confused in our electronics lab! Now you solve this! Thank you sir!
Great explanation!! Thank you for sharing your knowledge.
The best of all explanation I have seen !!!!, thank you!!!
I've got to learn from a rare explanation of such things, thank you very much sir may god bless you.
Great explanation!!!!!!! I will definitely subscribe. Pleas keep on making videos with this level of detail. I think you are the only youtuber i've seen explain the negative voltage on the capacitor.
Thank you! I appreciate that. If you have any suggestions, let me know. I do enjoy making these, so I will try to do more in the future
you just earned a like and a new follower, my friend
For a relative beginner in electronics, I learned about resistors, resistor colour codes, LED’s, capacitors, transistors. This circuit is a perfect example of how they can all interact with one another and achieve an end result, also the explanation of how it works was sublime. A big thank you. 👍🏼
Thank you, I'm glad my video helped you. Welcome to the world of electronics!
Awesome! Helped me so much. Thank you!
Great explanation, thanks mate
Awesome explanation... Couldn't be any better!!! Finally internalized the Magic...
Thank you!
I agree with all the comments. Finally I found the perfect explanation. You did it!!!
THE BEST explanation on YT! Finally! Thanks thanks and thanks! :)
Thank you! I appreciate that. Glad my video could help
the best explaination
Great video! Thanks for sharing your knowledge!
Thanks. Glad it was useful!
best explanation ever brother thank you
Thank you very very much Sir. The precise ,the best explanation amongst all that have been viewed on this topic. Helped also in understanding something about Capacitor.Simply great.
Thank you. I'm happy you found it useful!
@@GlevoTec Thank you once again.A novice query.will the opposite side of +side of capacitor get positively charged as this will result in .7v to trigger the base . Also both sides of each capacitor are connected to+ve supply voltage through different value resistors
@@adinath1974 Yes, each capacitor gets charged like is explained in the video. And yes, the values have to be different to allow the charging behaviour
This is becoming interesting. Each side of electrolytic capacitor is connected to +ve voltage with different value resistors. So each capacitor must be charging with different voltages on each side. Is it correct? However for frequently the higher value resistor is considered though there are 2 resistors on opposite side. Can you help with explanation. Or any literature you can provide for understanding some concepts.Thanking you in advance.
@@adinath1974 They don't charge with different voltages, since they're both connected to the same supply voltage Vcc. But they do reach their voltage level at different rates, because of their difference in value. The resistor at the LED has te be low to allow for quick charging that side of the capacitor. That way there is a decent difference in current supplying both sides of the capacitor, making sure the capacitor charges with this behaviour. Basically the smaller resistor only has to make sure the positive side of the capacitor can rise quickly to Vcc again after the transistor opens
Wow!! u have solved my problem
In order to simulate this on Lt spice what I should put for the dc operating point
i dont know how should i thank you, i am looking for this kind of explanation for years ,you are most genious i have ever seen, may allah bless you
Thank you. I'm happy my video could help you!
@@GlevoTec we want more this kind of videos, please help us by your knowledge, i think electronics nothing but playing with electrons that you have proved
can i have your facebook id?
Great explanation. Thanks.
Thank you!
I laughed and was so happy to watch this video, I'm a software eng from 90s and i can understand today's kids can't imagine what kind of dev environment we have been using in past, same is the case with electronics, today for learning purpose they use MCU to blink LED :)
Glad to read this. Exactly, most people of current generation don't know how it was done, or where it all comes from. I feel it's part of knowledge and understanding to get a deeper feeling for it when designing something.
This is really helpful. Also you talk like Dracula and that is pretty cool.
Thank you! First time somebody mentions that I sound like Dracula, so thanks, I guess haha
@@GlevoTec It's a good look man.
Very helpful. thank you.
well you made project easier
The time constant of the capacitor depends on the series resistance .Is that true? I dont understand. Help me.
great vid thx...keep up the good work!
Thank you!
Thank you for the video! This was really helpful to understand. Especial thanks to the part that explains the Component tolerances and the part where the capacitor flip the voltage. Could you please, explain why the Frequency is 1/(1.38xRC)?
Thanks you! The frequency is determined by the charging and discharging of the capacitors to the critical voltage at the transistors base. This depends on the time constants of the RC combination and the non-linear charge behaviour of the capacitors. For more info, take a look at capacitor charging curves and calculations
How is that equation derived for frequency?
Amazing!
I am on a journey trying to understand the Astable Multivibrator circuit. It's funny how you think you have a good idea on how the components work but realise, when digging into this system how much more complicated it is to truely understand due to the voltage drop and build up to 0.7V again for the base of the transistor to turn on again. I'm slowly getting there with the help of this video but understanding this curcuit in a fundamental way was a bigger task than I anticipated. Quite frustrating when it's supposed to be "simple" but I had to learn the fundamentals of something I thought I had a good idea about. I hate feeling dumb :)
That's the best way to learn. Digging deep to find what it is that's really making something work underneath. Simple circuits can sometimes be unexpectedly complex and circuits that seem complicated can actually just be a combination of very easy logical circuits. Good luck in your journey. Feeling "dumb" only means you're learning and getting better at it 👍
Better than others indian TH-camrs
Quiescent current in this ?
Hey, I just had a question about the equation at the end. Is there a book explaining the derivation of it?
4:48 so at certain point both LEDs light up. But that happens really fast that your eyes can't catch it.
and it never goes off at the same time. Do I understand it right?
must say.........it helped a lot.....too much....thanks.......... :)
Woow excellent 👍
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So at one point, the two sides of the capacitor are positively charge because the capacitor side between collector and the led could prevent electrons moving both sides, is that correct bro? But why is not both capacitors charged at the same amount at the same since the have the same resistance?
Sir, I am a TH-cam learner in electronics. I want to light up led on single wire parallel connection ,one led -ve +ve another one +ve -ve.
Can you make a simple circuit with pnp and npn transistor. At present I am getting this from quartz clock board. Can you help me.
Amazing I just wanted to know if it is possible to switch ac led series light with this circuit.
This circuit only works with dc. You could use a relay maybe
@@GlevoTec I thought of it but it would make alot of noise. Actually I have got a ac decoration light which I needed to alternate so I was searching for circuits.anyways ur video was great I learnt how the circuit works .
I get it now. Took me a month
I love this video and it was a great start for me to figure out how this basic schematic works. Thank you. But still I do not catch about voltage difference over capacitor remains, which are talking about ~4minute. And how does the voltage goes from 0.7 to -11.3 on the left side I could not get it. Can you please share some reference to read more about it? Is this about field effect or displacement current?
Thank you. The voltage difference is simply the capacitor voltage. When charged it acts as a battery, with a charge voltage difference between the two sides. The voltage "flip" only happens because the reference point changes. The voltage over the capacitor remains the same,. Only the measured voltage referenced to ground will become negative.
But why do the capacitors charge up through the bigger resistor?
Thanks 👍
i am not an electronic guy but likes electronic circuits very much ,can you show me how to use the flip flop circuit to convert DC to AC
thank you for the tutorial. i am learning it and i tried to build this circuit but both lights glow oneweaker than the other but they do not flash, i had 330 ohm and 33k resistors. i used 33MFD capacitors and n2222 transistors. am i using the wrong values?
At 33uF and 330 ohms your frequency will be too high to see. That's why you see the glow. It probably is oscillating, just too fast to see. Try different values and use the formula I show in the end of the video to calculate your component values for a low frequency between 1-10Hz
@@GlevoTec thank you very much
I'm a little confused. I followed another video that used a breadboard to build it. But the version I have seems to be all in reverse. The base of my transistors are connected to the positive of the capacitors, my positive battery lead is connected to the emitter of the transistors, the LEDs and resistors are connected between the collector of the transistors and the negative of my batteries. But it all works. Can anyone help me understand why this works, I am very new to all of this. Edit: or tell me what to look into lol
I had to click on 10 different videos before someone explained how it worked
Is it possible to use this to create sound by raising the hertz to the level of musical notes and wiring a speaker?
Yes you can. By using small capacitors such as 0.01uF. This increases the frequency to an audible level.
@@nathancantwell602 I've since tried this and it does work, but it gets unstable. It's not practical exactly
Great!!
This is a great video. However I have one doubt, are the capacitors electrolytic? If so, then how are we able to charge them through the cathode? This is bothering me very much. Hope you can clear it out. Thanks in advance!
Thanks. The capacitors are indeed electrolytic. But they don't have to be necessarily. They can take a small negative voltage without getting damaged
GlevoTec Appreciate the help, thanks!
I am like you! In every course I see the RC costant, charge/discharge cycle and then this circuit where the polarity is switched!
This is bothering me a lot, as well.
Anyway, this video is very clear about the circuit; on of the best I have seen!
What about 1 blinking and one static
It seems that the capacitor is charge over the resistance of the LED.
SIR:
VERY OUTSTANDING THE WAY OF DEMONSTRATING THE WORKING ELECTRONICS.
PLEASE TELL ME IF THE POLARIZATION OF CAPACITORS ARE OK IN THE SCHEMATICS. I THING ARE THERE IS SOMETHING RARE.
JOSÉ
Thank you. Yes, the polarization of the capacitors is correct, that's how it should be. Like mentioned, there is a slight reverse polarization, but that won't damage the capacitors.
great video, but it is confusing saying that "open transistor is not conducting".
Hi, when I simulate this circuit in simetrix I see both the LEDs lights up in the initial condition then they settle to flip flop oscillation.
Could you explain this initial condition?
Thanks
That's because your simulation doesn't account for the slight tolerance on the components. Like I said in the video. In real life because of those tolerances, one transistor will reach the open state slightly sooner than the other. So, in real conditions they won't open at the same time initially. Hope this helps!
change one capasitor into 99uf and other into 100uf. that will one simple answer to tolerance problem....ha ha
I believe the video's description of the initial capacitor charging is backwards. On a very short timescale, the capacitors act as a closed switch until they are charged, so the current flows through the LED and capacitor. This current also flows through the transistor bases, and eventually causes one of the transistors to conduct. The capacitor connected to the collector of that transistor then reverses its current flow. The other capacitor continues to build up a positive charge on the LED side, until it pushes the voltage of the LED cathode high enough that it can't conduct and turns off. If you were to begin with one of the capacitors fully charged, this initial two-led state shouldn't happen.
It works because the variance in the tolerances of the components. That's why it throws people off, because if the components were EXACTLY equal in their values it wouldn't work. Or you would have to short out a couple legs of a transistor quickly to get it to oscillate. (I've had to do that).
what type of wave is being created in this oscillator and how can we change that to other type of waves, please help me understand.
This outputs a square wave. You could change that to a sinewave or triangle wave with RC-filters
Hi.why 1.38?
The wires connecting the capacitors and their opposite transistors are not connected in between .are they ?
My circuit has those wires insulated but still the circuit works fine
No, they just cross. Like said in the video, the circuit consists of 2 identical parts. Each capacitor-transistor pair is a separate part. Not connected in between. This would disrupt the circuit.
Whats the best way to make one led blink.
Simply remove the other LED with a wire
Don't you need to replace the LED with a diode instead of just removing it ?
Thank you for your great video :)
The LED acts as a load. So you can simply remove it, as long as you keep a resistance there to charge the capacitor.
@@GlevoTec thanks. I realize that I lack a lot of knowledge to properly understand only that simple circuit!
@@vincentletard7379 No problem. To be fair, it is not so difficult as it looks. You just need to get the principle. Anyway, always keep learning!
Will a 2222a transistor work?
Yeah sure. Any general purpose NPN transistor will work.
what is the minimum and maximum dc supply for this circuit
The minimum voltage can be around 3V. Maximum voltage is defined by the transistors and capacitor's rating. The circuit works best above 5V in my experience
@@GlevoTec Will the circuit blow up with 9v or 12 v battery?
BTW thanks for your reply 😊
@@abhishekgupta9705 It will work perfectly. The circuit in the video was tested at 12V
I've found arduino and other microcontrollers end up just being solutions looking for problems. Why 1.38 in the frequency calculation? I'm going to assume I can use 2 variable resistors so long as they're both equal value and adjusted equally an try with my kid but I know she'll ask me why 1.38.
I like your Style
I can't understand how the capacitor gets charged from the branch with the higher resistance?! The negative terminal of the cap is on that side. My understanding is that it should be charged through the branch that has the led and lower resistor value since the positive terminal of the cap is on that side. Please help me understand this.
The negative terminal gets charged because the positive terminal is grounded when the transistor is closed. This means during that time, the positive terminal cannot charge, no matter what the resistor value is. It's grounded, so any charge current will flow to ground.
the negative voltage thing looks like magic. 🤔
About the oscillation, are the sine waves square or not?
The output is a square wave. The transition happens quickly
GlevoTec oh ok thank you so much!
@@GlevoTec you mentioned you can change it into a different wave in another comment using RC filters, I think. Could you output this wave with a speaker to make sound if you raised the hertz to the ballpark of musical notes?
@@TheD736 Yes, it's possible to create higher frequencies. But the circuit can become unstable.
Am Walid from Tunisia
How to break the initial balance?
The slight tolerance in the components will do that.
i dont get why one side of the cappacitor is 0v
Why current not going through base pin while capacitor is charging
Because the voltage at the base can't rise over 0,7V as long as the capacitor isn't charged to that voltage yet. The capacitor needs to reach +0,7V first, before the transistor base starts drawing any current. That's because of the base-emmiter junction that has a treshhold of around 0,7V, similar to a diode. I hope that's clear
@@GlevoTec can you clearefy by making a video about this please
@@GlevoTec but when capacitor is charging low currant should go through the base pin isn't?
Why current starts to flow in base pin after the capacitor is charg?
@@harshal3692 No. See the capacitor as a bucket of water. The top of the bucket is 0,7V, which is the treshold voltage of the transistor. Imagine the transistor is the table the bucket is on. The only way the water can get on the table is by filling the bucket until the top until it flows over. While filling, not even a little bit can get on the table, because it has to reach that treshold first to be able to flow. The capacitor acts the same way. It takes all the current available until it's charged up to 0,7V. At that point the transistors base will start drawing current because it has reached the treshold. At that moment the current will flow both to the capacitor and transistor base
@@GlevoTec can you explain by making video please
Cool bro , explanation very good, but you not teach how that componen united
🤗🤗
There is a mistake in the explanation. In the beginning of explanation, you said that the charging current will pass through 22k resistor towards the capacitor. But the passage of this current is still open circuit in Q1. Current will not move and will not charge in open circuit !!
You said "because of component tolerances". So... the blinking effect is based on a random (not calculated) effect.. tolerances. I wouldn't call this design accuracy. In other words, what should a circuit designer do, in order to make sure which capacitor will charge first?
No, the blinking effect is based on calculations. It is relatively stable and predictable when running. Just the starting situation is determined by the very small differences in tolerance. If you want a certain capacitor to charge first, you'll just make one a smaller value, or the other one bigger. But for this circuit that has no point, cause you want the values to be nearly equal.
@@GlevoTec Thanks. It is so interesting... placing components symmetrically, with the same specs, yet they may act so differently.
Still dont understand how capacitor charge from cathode...
The negative plate of the capacitor is not charging. The voltage of the negative plate returns to normal as the capacitor is discharged. You confused everyone.
Which is exactly what I am saying.
@@GlevoTec no
SIR:
I DONT KNOW WHY A LOT OF PERSONS WROTE THAT THEY CONSTRUCT THE GADGET AND WORKS. DEFINITIVELY THE POLARIZATION IS CROSSED OVER.
JOSÉ
Good video and the circuit works. But it does not really make sense. The capacitor gets charged a tiny bit through the big resistor at the base, then the transistor is switched on and it gets charged from the other side because there is less resistance. But then the capacitor should not discharge, it should always be charged and the second transistor should never switch on. Because the capacitor is charged through the voltage source it should never discharge.
Not really. Both sides of the capacitor charge at the same time, just at different rates. By reaching the threshold of 0.7V, one of the transistors closes. This causes the negative voltage, which keeps the other transistor closed. But because of the larger resistor, it will charge that side of the capacitor back towards 0,7V, causing the same to happen on the other side. It's not the charging that's controlled by the transistors, only the discharging
@@GlevoTec Thanks for the explanation. It is just hard to understand that a capacitor gets positive charge from both sides at the same time.
@@radio_electronics4047 Yeah, but you have to see a capacitor as nothing more than the difference in charge between two plates. Doesn't matter if one side is connected to ground or through a resistor to vcc. Simply the buildup of electrons on the plates determines the relative voltage between them. If you use different resistors like here, one plate will charge quicker than the other. Hope it helps!
@@GlevoTec i have same question in my mind it
really doesnt make any sense can you please explain it plssssssssssssssssssssssssssssss.......................
You made it really confusing by changing the transistor to switch an diode pair... I wonder how people call it the best explanation...
bad exp.
2:00 how come it's VCC? Isn't there a voltage drop across LEDs? Why aren't the LEDs turned on at the very beginning since the base->emitter allows for the current flow (otherwise how would the capacitor charge?)
It's VCC because at that point there is no current flowing through the LED. No current through a load, means no voltage drop. The LEDs are not turned on as long as the transisitor's base doesn't reach the treshhold voltage of 0.7V.
@@GlevoTec Thanks, that makes sense now!