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the sentences here are awful. can someone with a good knowledge of the English language pls have a look at it? -- zeno
Completely rewritten 5/11/03 - i hope it meets with approval from former contributors GRAHAMUK 23:05, 4 Nov 2003 (UTC)
I've expanded this section considerably. Sorry to delete existing text, but I think it had some problems, particularly references to capacitors discharging when they were actually charging.
Terra
Green
20:10, 10 January 2006 (UTC)
Thank you for the above explanations. My apologies to Graham if I actually introduced more problems when I thought I was "correcting" the text. I can now see where I was going wrong. I was thinking of the base of the transistor as being high impedance. Of course this is wrong, you are right the BE junction will look like a diode so will conduct if the base voltage exceeds 0.6V. That error was what led me to think the capacitor will be discharging, when it will in fact be reverse-charging as you say, and I think the other problems in what I wrote are all follow-on consequences of assuming zero base current. Sorry, it's too long since I've done any electronics, and maybe it was foolish of me to make such a major edit when I'm so rusty... Anyway, I wholeheartedly agree with you that the best thing would be some annotated plots of waveforms. If you are willing to do that, then that would be fantastic. Terra Green 22:30, 11 January 2006 (UTC)
Another thing which will almost certainly still need changing is what I wrote about the output voltage during state 1, as this too was based on the assumption of zero Q1 base current. But I'll leave it to others to make the change, because I'm now getting muddled when trying to think about it. Terra Green 23:01, 11 January 2006 (UTC)
Please repair the Astable Multivibrator Circuit section. First paragraph speaks of "suggested values" when there are no "suggested values". Much further down the article are the "suggested values". 14:10, 19 February 2010 (UTC) —Preceding unsigned comment added by 68.11.173.188 ( talk)
I've read this circuit, and I was a little confused as to why "C1" charges first. I eventually understood that the minute differences in resistors or capacitors are what causes one capacitor to charge first. If I'm wrong about this, please clarify - and would it be possible to include that in the article? Thanks. — Preceding unsigned comment added by 172.129.110.171 ( talk) 01:54, 16 January 2013 (UTC)
Can someone take a look at this? I am willing to rewrite it but I don't know when I can get to it. I suggest just deleting the explanation of how an astable works if you can't nail it down.
The BJTs are current-operated devices. It is the displacement current through each cap and its connected base that switches Q1/Q2 on and off, not the base voltages going above and below Vt. The bases will nearly always be at the junction potential. You can build this circuit with FETs, but it requires some modification to make the transistors shut off. The way the description is currently worded suggests that the resistors must be tuned somehow to bias the bases around Vt. 69.207.129.45 ( talk) 12:39, 1 October 2010 (UTC)
I would like to replace this "Basic Mode of Operation" section with a paraphrased version from the following source: http://www.electronics-tutorials.ws/waveforms/astable.html. The author of the content has emailed me his permission to do so, so long as an inline reference points back to his website as the source of the explanation. (Which is what Wikipedia prefers anyway.) What's helpful about his explanation is his description of the states of "plate A and B" for capacitor C1. In general his write up if far more explicable than the current, rather skeletal list of bullet statements. Take a look at his explanation and let me know. Dgiroux ( talk) 18:23, 17 October 2010 (UTC)
Someone suggested merging the stubs into this article. This is a good idea. -- Wtshymanski 02:20, 27 July 2006 (UTC)
A definition is mysteriously not there. A multivibrator is not defined as something thats used to implement a variety of simple two-state systems. This needs to be more explicitely defined in the intro. Fresheneesz 22:20, 25 October 2006 (UTC)
There's an interesting circuit here: [ [2]] (about 2/3 down the page), which uses 3 transistors to have 3 states. Would be worth addin
I added details to the monostable multivibrator and redefined it with One-Shot as well. I think a One-shot link should be created to redirect to this page if they are looking for the electronic definition of a one-shot. Dante 16:26, 22 June 2007 (UTC)
It's kind of a strange schema for the monostable, applying the trigger to the base of Q2
doesn't seem correct.
Cmyalrm (
talk)
18:29, 12 March 2010 (UTC)
for the multivibrator equation f=1/(.693*R*C)
I'm wondering, is .693 more accurately represented by ln(2)? I'm no expert, just a hobbyist, but knowing that the capacitor equation is exponential, it seems to make sense.
?? Thanks in advance, and my apologies if I am mistaken. -- Smiley325 20:23, 30 October 2007 (UTC)
Somewhere, somehow, apparently the component values for the circuit[s] were removed. It would be nice to give practical ranges for them. Nikevich ( talk) 09:32, 24 November 2009 (UTC)
Moved from User talk: Oli Filth:
I saw that you deleted a section calling it "...one particular example circuit". Isn't this a derivation of the time-constant? It would be nice to have the derivation in the article somewhere. Mikiemike ( talk) 01:29, 28 December 2010 (UTC)
The general flavor is WP:NOR.
This article makes several general statements about MVs based upon specific instances. The results are often false. Multivibrators must have two passive networks. Multivibrators must have a capacitor.
Ref 1, the etuttle blog, is not WP:RS.
Glrx ( talk) 05:07, 24 January 2011 (UTC)
"The name "multivibrator" was initially applied to the free-running oscillator version of the circuit because its output waveform was rich in harmonics"
I always thought it was because earlier oscillators were electromechanical, i.e. they were literally vibrators. Gigs ( talk) 17:53, 22 May 2012 (UTC)
Is there a source that multivibrators must have two gain devices?
Why not one? Plenty of relaxation oscillators manage with that. Is there a sourceable statement that they can be excluded from this scope?
Why not five? Take an (odd) handful of inverters with a propagation delay, couple them into a ring and away they go. Again, is there a sourced statement that this cannot be counted as a multivibrator? Andy Dingley ( talk) 15:14, 25 September 2012 (UTC)
If they'd said two "gain devices" we'd be all set.multivibrator A relaxation oscillator employing two electron tubes to obtain the in-phase feedback voltage by coupling the output of each to the input of the other through, typically, resistance-capacitance elements.
What a great plan for simplifying the encyclopedia! Instead of all those confusing articles, let's just put everything that has four legs and fur under "Kitty". Or don't you think there's some educational and philosophical value in discriminating between a 555 and the classic two-device multivibrator? Let alone every other kind of relaxation oscillator (another term that I've yet to see properly discussed). I think the two-active-device cross-coupled topology needs its own article and all the other kinds of oscillators can be described elsewhere. It's not great nomenclature, but "multivibrator" is what people call it, not "that Eccles-Jordan-Abram-Bloch thing that makes square waves". -- Wtshymanski ( talk) 13:56, 26 September 2012 (UTC)
== Comments on the article ==I am new to this so please excuse my lack of fines in suggesting a change to the section for the Astable frequency calculation.
In solving the log equation for t assumption is made that Vbe << Vcc. Since Vbe~0.6v & Vcc = 5V this is a too big assumption. However by including Vce_Q2(on) into the equation there is no need for the above approximation. Thus
Vcap(t) = Vbe_Q1 - Vce_Q2, Vcapinit = Vbe_Q1 - Vcc + Vce_Q2
Since Vbe ~ 0.6V & Vce_Q2 = 0.2V Vbe_Q1 - Vce_Q2 = 0.4V while Vbe_Q1 + Vce_Q2 = 0.8V which creates a ratio of 2 to Compliment Vcc/2Vcc Thus the equation naturally comes out at solution Ln (2)
1. "This circuit is also known as a one shot."
The sentence should end with a noun after the adjective and "one shot" should probably need a hyphen.
2. "Thus C1 restores its charge and prepares for the next State 1 when it will act again as a time-setting capacitor...and so on... (the next explanations are a mirror copy of the second part of Step 1)."
This is not a good sentence. The part from the first three periods should be fixed.
3. I disagree with the use of Vcc. It's inconsistent with Figure 1 which has V+. If Vcc is preferred, then the figures should be modified. I propose the second option.
4. "RB < β.RC"
Is that dot really meant to be a *? If it is there should be a a properly written equation for the expression.
5. I do not understand why the monostable multivibrator, aside from having a description, also has a link to a separate article explaining how the circuit works that is pretty much the clone for the same. I don't even think the article should exist since this article covers the monostable vibrator anyway.
6. It would definitely help to have actual values of R and C for simulation purposes to verify the functionality of the circuits.
ICE77 ( talk) 02:13, 28 July 2015 (UTC)
re: 3) Vcc is the correct term, and consistent with the standard nomenclature Vce, Vbb, Vcer, Vces, Vceo etc, (for example V+ is obviously wrong with PNP transistors) , on the same topic it should mentioned that when Vcc exceeds about 7v, you will get zener action on Vbe, specifically when Veb exceeds VBES this will make the MV run faster than theory, Note Veb measures the same node as Vbe except that Veb has the emitter positive and the base negative (i.e. so Veb < 7v or Vbe > -7v are equivalent, the order of the subscripts catches many new EE's out) Salbayeng ( talk) 04:08, 14 February 2016 (UTC)
This article really needs a diagram showing the waveforms , it's much more obvious when you can see the base potential being negative for a long time, and ramping up to the trip point. like on this page
schoolphysics.co.uk
"Multivibrator" definition is probably lost in history. You can make one with a pair of RC cross coupled relays, possibly someone did this back in the 1800's but failed to publish a web-page. While you can make a "vibrator" with just one relay
Trembler_coil (Model T ford), two make it more accurate as a timer.
I would definitely define a multivibrator as requiring two cross coupled RC stages and two active inverting elements noting the classic multivibrator has two complementary outputs (this might not be a necessary requirement?) so for example you can alternately flash two light bulbs (as on a railway crossing)(a 555 can't do that). With two RC stages you can set each of the two delays independently of the other (a 555 can't do that).
The 555 is definitely not a multivibrator, it belongs to the class of integrator + schmitt trigger oscillators, and has only one capacitor there are two basic topologies for the 555 , producing approximately sawtooth (classic relaxation oscillator) or triangle wave timing waveforms, the 555 explicitly sets the threshold voltages.
The other thing that isn't mentioned is that the output voltages on the collecters have a soft leading edge, and this may be undesirable in some applications (transistors get hot).
Historically, I have located Charles Adlers probably first patent on alternating flashing railway lights
US patent 1622018 and this is not a multivibrator, just a mono-vibrator with a heavy weight. So no real evidence for my earlier suggestion of cross coupled relays being the precursor to multivibrators.
Salbayeng (
talk)
02:34, 14 February 2016 (UTC)
Hi Has anyone considered adding some of the content that appears on the polish version of this article https://pl.wikipedia.org/wiki/Multiwibrator ?. It is about twice as long, and has more schematics including the triple-vibrator. Salbayeng ( talk) 04:19, 14 February 2016 (UTC)
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the sentences here are awful. can someone with a good knowledge of the English language pls have a look at it? -- zeno
Completely rewritten 5/11/03 - i hope it meets with approval from former contributors GRAHAMUK 23:05, 4 Nov 2003 (UTC)
I've expanded this section considerably. Sorry to delete existing text, but I think it had some problems, particularly references to capacitors discharging when they were actually charging.
Terra
Green
20:10, 10 January 2006 (UTC)
Thank you for the above explanations. My apologies to Graham if I actually introduced more problems when I thought I was "correcting" the text. I can now see where I was going wrong. I was thinking of the base of the transistor as being high impedance. Of course this is wrong, you are right the BE junction will look like a diode so will conduct if the base voltage exceeds 0.6V. That error was what led me to think the capacitor will be discharging, when it will in fact be reverse-charging as you say, and I think the other problems in what I wrote are all follow-on consequences of assuming zero base current. Sorry, it's too long since I've done any electronics, and maybe it was foolish of me to make such a major edit when I'm so rusty... Anyway, I wholeheartedly agree with you that the best thing would be some annotated plots of waveforms. If you are willing to do that, then that would be fantastic. Terra Green 22:30, 11 January 2006 (UTC)
Another thing which will almost certainly still need changing is what I wrote about the output voltage during state 1, as this too was based on the assumption of zero Q1 base current. But I'll leave it to others to make the change, because I'm now getting muddled when trying to think about it. Terra Green 23:01, 11 January 2006 (UTC)
Please repair the Astable Multivibrator Circuit section. First paragraph speaks of "suggested values" when there are no "suggested values". Much further down the article are the "suggested values". 14:10, 19 February 2010 (UTC) —Preceding unsigned comment added by 68.11.173.188 ( talk)
I've read this circuit, and I was a little confused as to why "C1" charges first. I eventually understood that the minute differences in resistors or capacitors are what causes one capacitor to charge first. If I'm wrong about this, please clarify - and would it be possible to include that in the article? Thanks. — Preceding unsigned comment added by 172.129.110.171 ( talk) 01:54, 16 January 2013 (UTC)
Can someone take a look at this? I am willing to rewrite it but I don't know when I can get to it. I suggest just deleting the explanation of how an astable works if you can't nail it down.
The BJTs are current-operated devices. It is the displacement current through each cap and its connected base that switches Q1/Q2 on and off, not the base voltages going above and below Vt. The bases will nearly always be at the junction potential. You can build this circuit with FETs, but it requires some modification to make the transistors shut off. The way the description is currently worded suggests that the resistors must be tuned somehow to bias the bases around Vt. 69.207.129.45 ( talk) 12:39, 1 October 2010 (UTC)
I would like to replace this "Basic Mode of Operation" section with a paraphrased version from the following source: http://www.electronics-tutorials.ws/waveforms/astable.html. The author of the content has emailed me his permission to do so, so long as an inline reference points back to his website as the source of the explanation. (Which is what Wikipedia prefers anyway.) What's helpful about his explanation is his description of the states of "plate A and B" for capacitor C1. In general his write up if far more explicable than the current, rather skeletal list of bullet statements. Take a look at his explanation and let me know. Dgiroux ( talk) 18:23, 17 October 2010 (UTC)
Someone suggested merging the stubs into this article. This is a good idea. -- Wtshymanski 02:20, 27 July 2006 (UTC)
A definition is mysteriously not there. A multivibrator is not defined as something thats used to implement a variety of simple two-state systems. This needs to be more explicitely defined in the intro. Fresheneesz 22:20, 25 October 2006 (UTC)
There's an interesting circuit here: [ [2]] (about 2/3 down the page), which uses 3 transistors to have 3 states. Would be worth addin
I added details to the monostable multivibrator and redefined it with One-Shot as well. I think a One-shot link should be created to redirect to this page if they are looking for the electronic definition of a one-shot. Dante 16:26, 22 June 2007 (UTC)
It's kind of a strange schema for the monostable, applying the trigger to the base of Q2
doesn't seem correct.
Cmyalrm (
talk)
18:29, 12 March 2010 (UTC)
for the multivibrator equation f=1/(.693*R*C)
I'm wondering, is .693 more accurately represented by ln(2)? I'm no expert, just a hobbyist, but knowing that the capacitor equation is exponential, it seems to make sense.
?? Thanks in advance, and my apologies if I am mistaken. -- Smiley325 20:23, 30 October 2007 (UTC)
Somewhere, somehow, apparently the component values for the circuit[s] were removed. It would be nice to give practical ranges for them. Nikevich ( talk) 09:32, 24 November 2009 (UTC)
Moved from User talk: Oli Filth:
I saw that you deleted a section calling it "...one particular example circuit". Isn't this a derivation of the time-constant? It would be nice to have the derivation in the article somewhere. Mikiemike ( talk) 01:29, 28 December 2010 (UTC)
The general flavor is WP:NOR.
This article makes several general statements about MVs based upon specific instances. The results are often false. Multivibrators must have two passive networks. Multivibrators must have a capacitor.
Ref 1, the etuttle blog, is not WP:RS.
Glrx ( talk) 05:07, 24 January 2011 (UTC)
"The name "multivibrator" was initially applied to the free-running oscillator version of the circuit because its output waveform was rich in harmonics"
I always thought it was because earlier oscillators were electromechanical, i.e. they were literally vibrators. Gigs ( talk) 17:53, 22 May 2012 (UTC)
Is there a source that multivibrators must have two gain devices?
Why not one? Plenty of relaxation oscillators manage with that. Is there a sourceable statement that they can be excluded from this scope?
Why not five? Take an (odd) handful of inverters with a propagation delay, couple them into a ring and away they go. Again, is there a sourced statement that this cannot be counted as a multivibrator? Andy Dingley ( talk) 15:14, 25 September 2012 (UTC)
If they'd said two "gain devices" we'd be all set.multivibrator A relaxation oscillator employing two electron tubes to obtain the in-phase feedback voltage by coupling the output of each to the input of the other through, typically, resistance-capacitance elements.
What a great plan for simplifying the encyclopedia! Instead of all those confusing articles, let's just put everything that has four legs and fur under "Kitty". Or don't you think there's some educational and philosophical value in discriminating between a 555 and the classic two-device multivibrator? Let alone every other kind of relaxation oscillator (another term that I've yet to see properly discussed). I think the two-active-device cross-coupled topology needs its own article and all the other kinds of oscillators can be described elsewhere. It's not great nomenclature, but "multivibrator" is what people call it, not "that Eccles-Jordan-Abram-Bloch thing that makes square waves". -- Wtshymanski ( talk) 13:56, 26 September 2012 (UTC)
== Comments on the article ==I am new to this so please excuse my lack of fines in suggesting a change to the section for the Astable frequency calculation.
In solving the log equation for t assumption is made that Vbe << Vcc. Since Vbe~0.6v & Vcc = 5V this is a too big assumption. However by including Vce_Q2(on) into the equation there is no need for the above approximation. Thus
Vcap(t) = Vbe_Q1 - Vce_Q2, Vcapinit = Vbe_Q1 - Vcc + Vce_Q2
Since Vbe ~ 0.6V & Vce_Q2 = 0.2V Vbe_Q1 - Vce_Q2 = 0.4V while Vbe_Q1 + Vce_Q2 = 0.8V which creates a ratio of 2 to Compliment Vcc/2Vcc Thus the equation naturally comes out at solution Ln (2)
1. "This circuit is also known as a one shot."
The sentence should end with a noun after the adjective and "one shot" should probably need a hyphen.
2. "Thus C1 restores its charge and prepares for the next State 1 when it will act again as a time-setting capacitor...and so on... (the next explanations are a mirror copy of the second part of Step 1)."
This is not a good sentence. The part from the first three periods should be fixed.
3. I disagree with the use of Vcc. It's inconsistent with Figure 1 which has V+. If Vcc is preferred, then the figures should be modified. I propose the second option.
4. "RB < β.RC"
Is that dot really meant to be a *? If it is there should be a a properly written equation for the expression.
5. I do not understand why the monostable multivibrator, aside from having a description, also has a link to a separate article explaining how the circuit works that is pretty much the clone for the same. I don't even think the article should exist since this article covers the monostable vibrator anyway.
6. It would definitely help to have actual values of R and C for simulation purposes to verify the functionality of the circuits.
ICE77 ( talk) 02:13, 28 July 2015 (UTC)
re: 3) Vcc is the correct term, and consistent with the standard nomenclature Vce, Vbb, Vcer, Vces, Vceo etc, (for example V+ is obviously wrong with PNP transistors) , on the same topic it should mentioned that when Vcc exceeds about 7v, you will get zener action on Vbe, specifically when Veb exceeds VBES this will make the MV run faster than theory, Note Veb measures the same node as Vbe except that Veb has the emitter positive and the base negative (i.e. so Veb < 7v or Vbe > -7v are equivalent, the order of the subscripts catches many new EE's out) Salbayeng ( talk) 04:08, 14 February 2016 (UTC)
This article really needs a diagram showing the waveforms , it's much more obvious when you can see the base potential being negative for a long time, and ramping up to the trip point. like on this page
schoolphysics.co.uk
"Multivibrator" definition is probably lost in history. You can make one with a pair of RC cross coupled relays, possibly someone did this back in the 1800's but failed to publish a web-page. While you can make a "vibrator" with just one relay
Trembler_coil (Model T ford), two make it more accurate as a timer.
I would definitely define a multivibrator as requiring two cross coupled RC stages and two active inverting elements noting the classic multivibrator has two complementary outputs (this might not be a necessary requirement?) so for example you can alternately flash two light bulbs (as on a railway crossing)(a 555 can't do that). With two RC stages you can set each of the two delays independently of the other (a 555 can't do that).
The 555 is definitely not a multivibrator, it belongs to the class of integrator + schmitt trigger oscillators, and has only one capacitor there are two basic topologies for the 555 , producing approximately sawtooth (classic relaxation oscillator) or triangle wave timing waveforms, the 555 explicitly sets the threshold voltages.
The other thing that isn't mentioned is that the output voltages on the collecters have a soft leading edge, and this may be undesirable in some applications (transistors get hot).
Historically, I have located Charles Adlers probably first patent on alternating flashing railway lights
US patent 1622018 and this is not a multivibrator, just a mono-vibrator with a heavy weight. So no real evidence for my earlier suggestion of cross coupled relays being the precursor to multivibrators.
Salbayeng (
talk)
02:34, 14 February 2016 (UTC)
Hi Has anyone considered adding some of the content that appears on the polish version of this article https://pl.wikipedia.org/wiki/Multiwibrator ?. It is about twice as long, and has more schematics including the triple-vibrator. Salbayeng ( talk) 04:19, 14 February 2016 (UTC)