The extra resistors R3 and R4 might be there to prevent the caps from charging up too much. Note the 6v power supply (battery), but they may have been planning for an even higher voltage power source like 12v.

You may be right there but I dont believe they were planning it for to go on a higher voltage as this is a project book experiment (4x 1.5V dc batteries). Usually resisters with capacitors in this formation are used to limit the rate of charge of the capacitors arent they? In this particular decision-making circuit with on off switch, You may be right that it limits the charging voltage.

If the caps charge too high in voltage, when a transistor turns on it could bang the other transistor base emitter with a reverse voltage of more than -5 volts, which could damage the base emitter diode. Most of these transistors have a -5v limit on that.

Your correct according to the 2N2222. The transister used in this experiment was a "BC548" which I do not have but it seems to allow Veb 6V no problem.

You could do a simulation and see if the caps ever charge up to more than 5v with different power supply voltages.
For this exact design, it doesn't seem to be a problem because the LED's will drop some of that 6v as well as the base emitter diodes of the transistors, but they may have been planning for a higher voltage. A simulation would tell us for sure.

I definitely will do this when I learn to operate one of the sim software like LTSpice

This circuit is a multi-multivibrator, with three distinct states rather than just two like a regular multivibrator (It looks like three anyway).
Notice it is set up the same way just with an extra transistor, and as mentioned the power supply is limited to 5v or lower.

Does this circuit you attached oscillate between the following states? (assuming Q1 switched on first)
Q1 ON Q2 OFF Q3 OFF
Q1 OFF Q2 ON Q3 OFF
Q1 OFF Q2 OFF Q3 ON
Q1 ON Q2 OFF Q3 OFF

 

Most of those transistor multivibrator circuits do not have the R5 and R6 in your circuit:

This is a decision-maker circuit so when you cut off the main charging supply to the capacitors (switch labled "GO") the oscillating will stop and there will be only one transistor left on. Because the oscillating is so fast this will be a random transistor for the operator. It's sort of like the 8 ball decision-making toys

 

Looks like a cool unit. What kind of signals do you want to look at?

I purchased it to have a look at standing waves at frequencies (pitches) for a pre amped guitar I purchased

 

You may be right there but I dont believe they were planning it for to go on a higher voltage as this is a project book experiment (4x 1.5V dc batteries). Usually resisters with capacitors in this formation are used to limit the rate of charge of the capacitors arent they? In this particular decision-making circuit with on off switch, You may be right that it limits the charging voltage.



Your correct according to the 2N2222. The transister used in this experiment was a "BC548" which I do not have but it seems to allow Veb 6V no problem.
View attachment 308706
View attachment 308709


I definitely will do this when I learn to operate one of the sim software like LTSpice


Does this circuit you attached oscillate between the following states? (assuming Q1 switched on first)
Q1 ON Q2 OFF Q3 OFF
Q1 OFF Q2 ON Q3 OFF
Q1 OFF Q2 OFF Q3 ON
Q1 ON Q2 OFF Q3 OFF

Hi there,

Yes, the idea that the extra resistors were there to prevent a high reverse voltage to the base emitter of the transistors was just a pure guess I did not do any sort of analysis, yet. Maybe I'll get to try that later.
However, for the sake of timing involving the capacitors, the only thing needed is the base resistor from the base to the positive supply rail. In the three transistor circuit you can see this a little more clearly. The timing depends on the 10k resistors and the 22uf caps, that's the most significant. If you increase all the 10k resistors the timing slows down.

The states, I believe, of the three transistors are any two are on at the same time while only one is off. That means that at any given time, two of the LED banks are on and only one bank is off. That gives us these states for the 'off' transistors (and the other two would be 'on'):
Q1
Q2
Q3
So the 'off' state transistor sort of walks from Q1 to Q2 to Q3, then back to Q1, and just keeps repeating.
It's kind of an interesting circuit I think even though so simple.
Might be interesting to add more transistors too see what happens.
I'll try simulating later.

LT Spice has example circuits you could try first to get the hang of it.

 

Hi there,

Yes, the idea that the extra resistors were there to prevent a high reverse voltage to the base emitter of the transistors was just a pure guess I did not do any sort of analysis, yet. Maybe I'll get to try that later.
However, for the sake of timing involving the capacitors, the only thing needed is the base resistor from the base to the positive supply rail. In the three transistor circuit you can see this a little more clearly. The timing depends on the 10k resistors and the 22uf caps, that's the most significant. If you increase all the 10k resistors the timing slows down.

The states, I believe, of the three transistors are any two are on at the same time while only one is off. That means that at any given time, two of the LED banks are on and only one bank is off. That gives us these states for the 'off' transistors (and the other two would be 'on'):
Q1
Q2
Q3
So the 'off' state transistor sort of walks from Q1 to Q2 to Q3, then back to Q1, and just keeps repeating.
It's kind of an interesting circuit I think even though so simple.
Might be interesting to add more transistors too see what happens.
I'll try simulating later.

LT Spice has example circuits you could try first to get the hang of it.

Oh ok. Im having a hard to visualizing what causes one of the transistors to turn off on he 3 transistor model. I think you and k1ng 1337 are right, I need to use LTSpice. I am in the process of learning it and I think I'll learn Multisim too cause it looks cool

 

Oh ok. Im having a hard to visualizing what causes one of the transistors to turn off on he 3 transistor model. I think you and k1ng 1337 are right, I need to use LTSpice. I am in the process of learning it and I think I'll learn Multisim too cause it looks cool

Hi,

Yes, the four and five transistor versions are even harder to visualize. The five transistor version has two transistors off at any given time and there may be some overlap in the states of each transistor.

With LTSpice there are only a few things you have to learn to get started. These are the basics:
1. How to draw schematics, how to choose parts (easy, it's on the main menu). You can however start with an example circuit that comes with LTSpice.
2. How to set up the transient analysis (not too hard, just a few settings).
3. After RUN, choose which node voltage you want to measure with the mouse, or current through some component you want to measure.

 

With LTSpice there are only a few things you have to learn to get started. These are the basics:
1. How to draw schematics, how to choose parts (easy, it's on the main menu). You can however start with an example circuit that comes with LTSpice.
2. How to set up the transient analysis (not too hard, just a few settings).
3. After RUN, choose which node voltage you want to measure with the mouse, or current through some component you want to measure.

Thanks mate. I'll make sure I study up on these points before trying to simulate the circuits we've been talking about. I'll use 133t kings example program. Thanks again for that!

 

Thanks mate. I'll make sure I study up on these points before trying to simulate the circuits we've been talking about. I'll use 133t kings example program. Thanks again for that!

Hi,

You're welcome and if I get a chance later I will draw this circuit into LTSpice and post the file here. All you would have to do then is download the file and run the simulation.

When you start with LTSpice, first just try drawing a simple voltage divider with a voltage source or something like that. Maybe add a capacitor, then do a transient analysis. That would get you started. It's mainly about finding where everything is in the menu system they use. Once you find out how to get the parts from the menu and paste them into the drawing, then you just have to set the type of analysis and a couple other little things, then run it.

If you are this much into electronic circuitry, this will be the most interesting thing you have ever done in this area so it's well worth the time.

 

Hi all. I am looking at a new circuit which uses a switch to activate a fast switching astable multivibrator oscillator and when the switch is removed it stops the oscillating processes and only 1 or the transistors will remain on. (Its like a decision maker machine)

I understand mostly how the astable multivibrator works but only it its form without the human-operated switch. With the switch labeled "GO" and extra 2 paths with resisters R5 and R6 a have a question

Why does the astable multivibrator not continue to oscillate when the GO switch is either open or completely removed from the circuit due to the paths which I have colored in red and blue that seem to be a complete circuit to allow current continue charging the capacitors and allow current through the Base Emitter?

View attachment 308625

Hello again,

I am quoting your first post because this reply pertains to the original circuit.

It dawned on me that the reason for the extra resistors was probably because they simply wanted to design a circuit that was not JUST a multivibrator, but rather a multivibrator with memory.

Notice there is no switch for the 6v battery, which would be the more usual case. Instead, the switch is mid circuit and a momentary push button not a SPST switch, where you can push it to start the oscillation, and release it to stop the oscillation. When you stop the oscillation though, the circuit holds the very last state. That means whatever LED was on at the time of the release (or close to that time) will stay on, and so you will not lose the state.

That actual is sort of like a heads/tails coin flip, so most likely they were shooting for that kind of behavior rather than the usual simply multivibrator type of circuit which just keeps going and going.

 

Hello again,

I am quoting your first post because this reply pertains to the original circuit.

It dawned on me that the reason for the extra resistors was probably because they simply wanted to design a circuit that was not JUST a multivibrator, but rather a multivibrator with memory.

Notice there is no switch for the 6v battery, which would be the more usual case. Instead, the switch is mid circuit and a momentary push button not a SPST switch, where you can push it to start the oscillation, and release it to stop the oscillation. When you stop the oscillation though, the circuit holds the very last state. That means whatever LED was on at the time of the release (or close to that time) will stay on, and so you will not lose the state.

That actual is sort of like a heads/tails coin flip, so most likely they were shooting for that kind of behavior rather than the usual simply multivibrator type of circuit which just keeps going and going.

Sorry for the late reply I just seen this. Yep your analysis is correct. I only just realized it is a push button type switch when you told me now