I was going to say the same. I was 12 and it was my first electronic circuit. I didn't know how it worked, but I thought it must have been very complicated! Then the path for my future educations and carriers started from there. Another good thing I learned the digital electronics and gates.
I remember that column in Popular Electronics in the 70s "introducing LEDs" and this *very* *same* *circuit* was the first circuit I ever built that used LEDs! Thank you for bringing back joyous childhood memories! BTW: PNP == Pointing iN Proudly. NPN == Not Pointing iN. That's how I'll always remember it.
And you can have a problem running this on a 10v supply because the reverse breakdown voltage of the base is usually about 6v which this circuit is exceeding.
Yes. It works like a voltage doubler and one side of the cap gets the double the voltage. I just thought about the voltage doubler circuit. For the first stage the cap voltage gets up to almost the input voltage. For every other stage the input voltage is added to the previous stage. So for the first stage, the voltage gets doubled and the Vc is up to input voltage and so on.
Ahhhh, the good old astable multivibrator. Will always remember an electronics-instructor I had in the late 70’s. He always referred to the astable multivibrator as the “Epitome of Modern Electronics” whenever he explained it, which was a lot, as a lot of studentds just didn’t seem to be able to understand its operation.
I remember having a hangover the morning I first encountered this. Made it a little bit difficult to understand at first, but a large caffeine intake solved that.
After building a crystal set with the help of my father when I was about 7 or 8yo in the early 70s, this was the next circuit I built from a schematic using germanium transistors, thanks to my uncle who was an electric typewriter tech. He gave me the parts, and I constructed it on my own on a bit of wood, soldering the parts to panel pins. No LEDs back then. My version ran at about 1kHz or so with 100nF caps, so it was audio, feeding a crystal earpiece. While I didn't understand how it worked, the practical skills and confidence that I gained from building the circuit myself were key to forming the career I've followed ever since.
The multivibrator. Its name comes from its originally use as a replacement for mechanica vibrators used in the voltage step-up circuit required in tube car radios. I built one in 1961. The only transistors I could get were Germanium TO-3 package.
Don't know if you had "Ladybird" books in the states but in the UK they are kids books, and the one I had was about electronics and this was the first circuit the book explored except we had 6v bulbs off our bikes because LEDs hadn't been invented !...cheers.
The most unusual way to draw the astable multivibrator on the diagram )). Great explanation though. And yes, When pnp it is easier to use "+" as ground, like we did in 80s-90s. Germanium transistors were more common as pnp.
You can use this in a modified multivibrator circuit to create a nice inverter. There is a formula for selecting the correct caps for the timing to obtain 50 or 60 Hz.
Are the electrolytic caps backwards in the schematic? The base ends are always at a higher voltage than the collector ends, but the schematic puts the positive side of the caps at the collectors.
@@jontscott Indeed the transistor-base-side of the capacitors experiences a higher voltage than the LED side, yet the capacitors are shown polarized on the schematic with the - side toward this higher voltage. Furthermore, IMSAIGuy says that the capacitors discharge thru the LEDs, but since the LED side has the lower voltage while the 100k resistor side has the higher voltage, one would think that the capacitors would discharge thru the 100k resistors. Very confusing.
As you were describing the circuit, you referred to current flow. Flashbacks came, seeing some of my professors using current flow and others electron flow. Books would use one or the other. With years of therapy and counseling I was able to become a productive person. And then my TH-cam hero's brought it all back! Guess it's back to therapy. Please don't start with hole flow!
Fun and funny circuit for sure. It is the first "real" electronic circuit i built as a kid. With all kind of different LEDs i could find. Only red, green, yellow - but some different sizes was enough to have lots of fun. In fact one problem is the reverse voltage to the transistors E-B diode. I dont know a lot about 2N3906 - kind of exotic here in europe, but our standard types like BC558 and BC308 did not like more than ~5V in reverse 😉
I remember the NPN version of this--just flip everything upside down. Ran from 5V just fine. I want to say the schematic was on the back of some radio shack NPN resistors. Probably 2N3904 or 2N2222. I may still have it.
These circuits are always tough to wrap your head around. I have a challenge for you. Look at the Neon Light oscillator in the chopper circuit of a HP410C VTVM. How does that work?
@@IMSAIGuy It works because the neon bulb has non linear characteristics like UJT. This is called Pearson-Anson effect (from Wikipedia). I remembered when I was a teenager I asked if I could use an LED to do the same thing. The answer was no!
One of those simple easy circuits ,not so simple. Others had trouble with the circuit at lower voltages & higher current & had to use extra transistors. The diode not going to zero when off is one problem.
Im so fond and grew up on these circuits in late 70's, but nowdays I kinda lean toward uControllers - I get conflicted as I love these analog circuits and sometimes they are just simpler. example this circuit uses 9 components outside of the LEDs, today I just use a pic10F200, only 1 component, saves board space and I dont even need current limit resistors as the pic can only drive 20ma (as I recall) there was an appnote on directly driving led without series resistors - dont get me wrong, not pushing microcontrollers, but it sometimes seams like I force myself to use analog design sometimes
It is a self-killing circuit. Death is slow. With the supply voltage used the base-emitter junctions of the transistors are probably being subjected to reverse breakdown. They'll survive that if the current is limited, behaving very much like a zener diode. However, eventually the beta of the transistors will be degraded and the circuit will stop working. With the 10 volt supply it is probably right at the ragged edge of reverse breakdown of the B-E junctions. ON Semi specs the minimum reverse breakdown voltage of the 2N3906 as 5 V. No other spec is provided. That is quite typical of small signal silicon BJTs. Actual breakdown of around 7 volts is pretty common. [edit] In the circuit in the video the base current in reverse breakdown could be rather high since the only thing between the base of one transistor and the collector of the other is the charged capacitor. The transient current into the base could be tens of milliamps. It is kind of perverse to use PNP transistors only and call the negative side of the power supply "ground." Vcc is the negative side of the supply. Ground is positive. If you 'scope it that way, exactly what is going on at the bases is more conspicuous. In the early days of transistors germanium PNPs ruled.
@@ItsMe-yd6ms It's kind of awkward in this circuit. You could put inverse diodes across the B-E junctions, but that creates very rapid discharge paths for the timing capacitors. I don't see an easy fix that won't potentially interfere with the fast turn-off of one transistor when the other begins to turn on, and to at least some degree you need that to assure rapid, clean change of state. Something like a 3.9 volt zener in series with the diode might be OK in terms of performance (you need the zener _and_ the diode, otherwise the zener would just act as a simple diode in parallel with the B-E junction when the base was negative with respect to the emitter). A diode in series with the base _might_ be OK but the turn-off of the transistor will be slowed because there is no way to rapidly get the excess carriers out of the base region. I suspect that actually wouldn't matter in this circuit. [edit] If the zener and diode scheme were used there is no reason a single zener shouldn't be shared. In this circuit the zener anode would connect to the positive supply rail. Each transistor would get a conventional diode from its base to the cathode of the zener.
@@ItsMe-yd6ms I don't know of anything other than limiting the supply voltage so that the voltage applied to the transistor base won't exceed its reverse breakdown voltage. Anything else I can think of requires extra components.
It's amazing how many ways there are to flash LEDs. My favourite is using the CD4093 "CMOS Quad 2-Input NAND Schmidt Triggers" (that's TI's name for it :-). It only takes 1 resistor and 1 capacitor to make the astable flasher, and then 1 resistor per LED you wish to flash. Use 1 more of the nand gates to invert the output for the 2nd LED. And you still have 2 extra nand gates. And it runs on 3 to 15V and takes only a few microamps for the chip itself. The main drawback is that the frequency is limited to a few MHz depending on the supply voltage.
Oh I see. The same thing. But the 74C version probably has a more limited supply voltage range, but a higher frequency. I'm guessing at that. Anyway Merry Christmas soon to You and Imsai Dog :-) 🎄🪅🧸⛄🛷🪆🎅
@@IMSAIGuy And the 74HC14 can make 6 oscilators. The 4093 only 4. Lol. But I use my Arduino for everything nowadays. It's just one more way to flash LEDs. If you want 15 or so flashing LEDs, there you go. Lol.
@@IMSAIGuy BTW. Flashing LEDs is about the extent of my electronics knowledge. I am basically a computer programmer/system administrator for the past 40 years. Now retired and always looking for hobbies. So watching your videos is very educational for me. Thanks :-)
@@stamasd8500 There is such an electrical beast as a Relaxation Is Oscillator. Part of a High School Electronics Class involved assembling one. It uses two Neon Lamps instead of LEDs and showed the same alternating illumination pattern as the energy ping-ponged back and forth between two capacitors. The thing about the circuit is once it was powered up and running it took almost no energy to keep it going. Once you turned it off if you didn't short it the Capacitors the Neon Lights would keep flashing for a couple of minutes. It was kind of like an electrical equivalent of a Perpetual Motion Machine . Another tribute to Newton's 0th Law of the conservation of energy.
Sure. That is a far more common way to do this. The sole possible advantage of the PNP design is that the loads (LEDs) can connect to the negative side of the power supply. Basically just flip the schematic top to bottom, use the opposite polarity for the supply, reverse the polarity of the LEDs and use the NPN transistors. Note that with 220 ohm resistors in series with the LEDs you'll get about 35 mA through the LEDs with a 10 V power supply. That may be more than you want.
basically the transistors are not identical, the resistors are not perfectly equal, the capacitors are slightly different... and that creates an initial imbalance that propagates.
@@stamasd8500 Thanks, thought others would be interested as well. Kind of like why does a regular component oscillator start oscillating? Noise at the atomic level IIRC and of course the Barkhausen criteria that keeps it going.
With all due respect, your explaination of how this astable multivibrator circuit works is not totally correct. This circuit shall be seen as two inverting transistor amplifiers in cascade form such that the final output is fed back to the input, and that the gain of amplifiers are greater than 1. I can explain in details how and why this circuit works if someone is interested. :)
![[TH] VCT Masters Shanghai Playoffs DAY 3 // FNC vs FUT | EDG vs PRX](http://i.ytimg.com/vi/pw2T5v0ogDI/mqdefault.jpg)
I first built this circuit from a Forrest Mims III book when I was about 12, and it's still my favourite.
I did too, I still have my Forest Mimms books.
I was going to say the same. I was 12 and it was my first electronic circuit. I didn't know how it worked, but I thought it must have been very complicated! Then the path for my future educations and carriers started from there. Another good thing I learned the digital electronics and gates.
I remember that column in Popular Electronics in the 70s "introducing LEDs" and this *very* *same* *circuit* was the first circuit I ever built that used LEDs! Thank you for bringing back joyous childhood memories!
BTW: PNP == Pointing iN Proudly. NPN == Not Pointing iN. That's how I'll always remember it.
...and that mosfets are the other way around ;-)
And you can have a problem running this on a 10v supply because the reverse breakdown voltage of the base is usually about 6v which this circuit is exceeding.
You won't need to double up the voltage rating on the capacitors because the voltage across the capacitors will always be under the supply voltage
Yes. It works like a voltage doubler and one side of the cap gets the double the voltage. I just thought about the voltage doubler circuit. For the first stage the cap voltage gets up to almost the input voltage. For every other stage the input voltage is added to the previous stage. So for the first stage, the voltage gets doubled and the Vc is up to input voltage and so on.
Ahhhh, the good old astable multivibrator. Will always remember an electronics-instructor I had in the late 70’s. He always referred to the astable multivibrator as the “Epitome of Modern Electronics” whenever he explained it, which was a lot, as a lot of studentds just didn’t seem to be able to understand its operation.
I remember having a hangover the morning I first encountered this. Made it a little bit difficult to understand at first, but a large caffeine intake solved that.
After building a crystal set with the help of my father when I was about 7 or 8yo in the early 70s, this was the next circuit I built from a schematic using germanium transistors, thanks to my uncle who was an electric typewriter tech. He gave me the parts, and I constructed it on my own on a bit of wood, soldering the parts to panel pins.
No LEDs back then. My version ran at about 1kHz or so with 100nF caps, so it was audio, feeding a crystal earpiece. While I didn't understand how it worked, the practical skills and confidence that I gained from building the circuit myself were key to forming the career I've followed ever since.
The multivibrator. Its name comes from its originally use as a replacement for mechanica vibrators used in the voltage step-up circuit required in tube car radios. I built one in 1961. The only transistors I could get were Germanium TO-3 package.
isn't the capacitor polarized the wrong way round?
Don't know if you had "Ladybird" books in the states but in the UK they are kids books, and the one I had was about electronics and this was the first circuit the book explored except we had 6v bulbs off our bikes because LEDs hadn't been invented !...cheers.
I really appreciate when you describe circuits like these! Your explanations really help me to understand what’s going on. Thank you!
We used this type of relaxation oscillators in our radars, but they were tube type. The ranging circuits used multiple oscillators.
Eccles-Jordan multivibrator. Classic. One of fthe first circuit I have built. I also have tried to make a version with mosfets, but I have failed.
About 20 years ago I made a "business card" with this circuit. My first SMD project.
very well done; a lot learned from that simple circuit
The whole field of two -transistor relaxation oscillators is a fascinating one! Is there a summary somewhere of all the various types?
The most unusual way to draw the astable multivibrator on the diagram )). Great explanation though.
And yes, When pnp it is easier to use "+" as ground, like we did in 80s-90s. Germanium transistors were more common as pnp.
You can use this in a modified multivibrator circuit to create a nice inverter. There is a formula for selecting the correct caps for the timing to obtain 50 or 60 Hz.
Are the electrolytic caps backwards in the schematic? The base ends are always at a higher voltage than the collector ends, but the schematic puts the positive side of the caps at the collectors.
I was thinking the same thing... seems the caps should have been reversed... I guess at low currents they tolerate the reverse voltages.
@@jontscott Indeed the transistor-base-side of the capacitors experiences a higher voltage than the LED side, yet the capacitors are shown polarized on the schematic with the - side toward this higher voltage. Furthermore, IMSAIGuy says that the capacitors discharge thru the LEDs, but since the LED side has the lower voltage while the 100k resistor side has the higher voltage, one would think that the capacitors would discharge thru the 100k resistors.
Very confusing.
Great little circuit, please do more like this, simple and fun. Thanks for sharing 😊
My had was NOT raised. Good video.
Thanks again for the great teaching!
As you were describing the circuit, you referred to current flow. Flashbacks came, seeing some of my professors using current flow and others electron flow. Books would use one or the other. With years of therapy and counseling I was able to become a productive person. And then my TH-cam hero's brought it all back! Guess it's back to therapy. Please don't start with hole flow!
Fun and funny circuit for sure. It is the first "real" electronic circuit i built as a kid. With all kind of different LEDs i could find. Only red, green, yellow - but some different sizes was enough to have lots of fun. In fact one problem is the reverse voltage to the transistors E-B diode. I dont know a lot about 2N3906 - kind of exotic here in europe, but our standard types like BC558 and BC308 did not like more than ~5V in reverse 😉
Arrow always points to the "N", That's the way I was taught to remember this.
The arrow just shows the direction of emitter current, it is as simple as that.
I remember the NPN version of this--just flip everything upside down. Ran from 5V just fine. I want to say the schematic was on the back of some radio shack NPN resistors. Probably 2N3904 or 2N2222. I may still have it.
th-cam.com/video/BrirtA6fS70/w-d-xo.htmlsi=6I6AV4PeBUKjlrwu
@@IMSAIGuy TH-cam recommended that right after I got done with your pnp video.
I’m sure if you asked a young kid to make two LEDs flash alternately, he would immediately run to his Arduino and 3D printer. 😆
Lets talk about Unijunction transistors, the 555 of the 60's and early 70's !
And tunnel diodes while we're at it. :)
Yaaaaa@@stamasd8500
Clever. Tricky. Cap must be more than 10V = good point. Bravo!
For one end to be at 18v the other end has to be at 9v which means the cap still has less than 10v across it, so no problem with a 10v cap.
Cool! I did a video on these a few months ago. I used NPNs though.
These circuits are always tough to wrap your head around.
I have a challenge for you.
Look at the Neon Light oscillator in the chopper circuit of a HP410C VTVM.
How does that work?
similar: th-cam.com/video/BXD3DNALulQ/w-d-xo.htmlsi=KfhA5j16CAxcmTSU
@@IMSAIGuy It works because the neon bulb has non linear characteristics like UJT. This is called Pearson-Anson effect (from Wikipedia). I remembered when I was a teenager I asked if I could use an LED to do the same thing. The answer was no!
One neat things about this circuit is that you get -9V to 9V swinging signal if you measure both collectors.
One of those simple easy circuits ,not so simple. Others had trouble with the circuit at lower voltages & higher current & had to use extra transistors. The diode not going to zero when off is one problem.
Im so fond and grew up on these circuits in late 70's, but nowdays I kinda lean toward uControllers - I get conflicted as I love these analog circuits and sometimes they are just simpler. example this circuit uses 9 components outside of the LEDs, today I just use a pic10F200, only 1 component, saves board space and I dont even need current limit resistors as the pic can only drive 20ma (as I recall) there was an appnote on directly driving led without series resistors - dont get me wrong, not pushing microcontrollers, but it sometimes seams like I force myself to use analog design sometimes
astable multivibrator :> at the time i lacked the context to know why they used such a weird name
PNP, pee n the pot and NPN, not peeing in the pot. It just stuck with me the first time I heard it this way when I was a kid.
It is a self-killing circuit. Death is slow.
With the supply voltage used the base-emitter junctions of the transistors are probably being subjected to reverse breakdown. They'll survive that if the current is limited, behaving very much like a zener diode. However, eventually the beta of the transistors will be degraded and the circuit will stop working.
With the 10 volt supply it is probably right at the ragged edge of reverse breakdown of the B-E junctions. ON Semi specs the minimum reverse breakdown voltage of the 2N3906 as 5 V. No other spec is provided. That is quite typical of small signal silicon BJTs. Actual breakdown of around 7 volts is pretty common.
[edit] In the circuit in the video the base current in reverse breakdown could be rather high since the only thing between the base of one transistor and the collector of the other is the charged capacitor. The transient current into the base could be tens of milliamps.
It is kind of perverse to use PNP transistors only and call the negative side of the power supply "ground." Vcc is the negative side of the supply. Ground is positive. If you 'scope it that way, exactly what is going on at the bases is more conspicuous. In the early days of transistors germanium PNPs ruled.
So how would you prevent this death? Use NPNs with voltages closer to the ground level?
@@ItsMe-yd6ms
It's kind of awkward in this circuit.
You could put inverse diodes across the B-E junctions, but that creates very rapid discharge paths for the timing capacitors. I don't see an easy fix that won't potentially interfere with the fast turn-off of one transistor when the other begins to turn on, and to at least some degree you need that to assure rapid, clean change of state. Something like a 3.9 volt zener in series with the diode might be OK in terms of performance (you need the zener _and_ the diode, otherwise the zener would just act as a simple diode in parallel with the B-E junction when the base was negative with respect to the emitter). A diode in series with the base _might_ be OK but the turn-off of the transistor will be slowed because there is no way to rapidly get the excess carriers out of the base region. I suspect that actually wouldn't matter in this circuit.
[edit] If the zener and diode scheme were used there is no reason a single zener shouldn't be shared. In this circuit the zener anode would connect to the positive supply rail. Each transistor would get a conventional diode from its base to the cathode of the zener.
@@d614gakadoug9 Is there a way to make a 2-transistor astable multivibrator without these problems?
@@ItsMe-yd6ms
I don't know of anything other than limiting the supply voltage so that the voltage applied to the transistor base won't exceed its reverse breakdown voltage. Anything else I can think of requires extra components.
A diode in series with each emitter lead is standard practice to prevent breakdown.
It's amazing how many ways there are to flash LEDs. My favourite is using the CD4093 "CMOS Quad 2-Input NAND Schmidt Triggers" (that's TI's name for it :-). It only takes 1 resistor and 1 capacitor to make the astable flasher, and then 1 resistor per LED you wish to flash. Use 1 more of the nand gates to invert the output for the 2nd LED. And you still have 2 extra nand gates. And it runs on 3 to 15V and takes only a few microamps for the chip itself. The main drawback is that the frequency is limited to a few MHz depending on the supply voltage.
th-cam.com/video/o31_fnTqUOw/w-d-xo.htmlsi=cmuF2s5oRmhDvrwO
Oh I see. The same thing. But the 74C version probably has a more limited supply voltage range, but a higher frequency. I'm guessing at that. Anyway Merry Christmas soon to You and Imsai Dog :-)
🎄🪅🧸⛄🛷🪆🎅
the HC is good to 7V the C part is good to 18V@@robinbrowne5419
@@IMSAIGuy And the 74HC14 can make 6 oscilators. The 4093 only 4. Lol. But I use my Arduino for everything nowadays. It's just one more way to flash LEDs. If you want 15 or so flashing LEDs, there you go. Lol.
@@IMSAIGuy BTW. Flashing LEDs is about the extent of my electronics knowledge. I am basically a computer programmer/system administrator for the past 40 years. Now retired and always looking for hobbies. So watching your videos is very educational for me. Thanks :-)
hmmm, nice to have an oscilloscope!
Do you know any good experiments for demonstrating rlc circuits?
Colpitts or Hartley
Hmmm. A Relaxation Oscillator
you are getting sleepy.....sleeeeepy...
Yes it's very relaxing.
@@stamasd8500 There is such an electrical beast as a Relaxation Is Oscillator. Part of a High School Electronics Class involved assembling one. It uses two Neon Lamps instead of LEDs and showed the same alternating illumination pattern as the energy ping-ponged back and forth between two capacitors. The thing about the circuit is once it was powered up and running it took almost no energy to keep it going. Once you turned it off if you didn't short it the Capacitors the Neon Lights would keep flashing for a couple of minutes. It was kind of like an electrical equivalent of a Perpetual Motion Machine . Another tribute to Newton's 0th Law of the conservation of energy.
I’m curious if you dabble in circuit bending?
I'm skilled in all the black arts 😎
@@IMSAIGuy In future episodes, can you share some helpful tips on circuit bending. Thanks
Could I reverse the polarity and build this w/ 2N2222s or 2N3904s?
Sure. That is a far more common way to do this. The sole possible advantage of the PNP design is that the loads (LEDs) can connect to the negative side of the power supply.
Basically just flip the schematic top to bottom, use the opposite polarity for the supply, reverse the polarity of the LEDs and use the NPN transistors. Note that with 220 ohm resistors in series with the LEDs you'll get about 35 mA through the LEDs with a 10 V power supply. That may be more than you want.
NPN: th-cam.com/video/BrirtA6fS70/w-d-xo.htmlsi=wBthn_89SNSyI4ck
Can you make a video about simple LED flashed based on Schmitt trigger like schematics 2 BJTs and just one capacitor?
here is schmitt oscillator. just make it slow
th-cam.com/video/o31_fnTqUOw/w-d-xo.htmlsi=rKMN-owzPRghwJj-
Ahh, but the proverbial question...which side turns on first and why? ;-)
ask Mr Heisenberg
basically the transistors are not identical, the resistors are not perfectly equal, the capacitors are slightly different... and that creates an initial imbalance that propagates.
@@stamasd8500 Thanks, thought others would be interested as well. Kind of like why does a regular component oscillator start oscillating? Noise at the atomic level IIRC and of course the Barkhausen criteria that keeps it going.
What book is this from ?
popular electronics was a magazine
i got a maple board and put brass tracks in to solder this circuit to. a literal bread board😅 people don’t appreciate art.
nowadays you can't afford maple
With all due respect, your explaination of how this astable multivibrator circuit works is not totally correct. This circuit shall be seen as two inverting transistor amplifiers in cascade form such that the final output is fed back to the input, and that the gain of amplifiers are greater than 1. I can explain in details how and why this circuit works if someone is interested. :)