Head and Tails circuit - urgent!!

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zaibatsu2000

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i am sorry guys...i think it is kinda bad to ask a question and expect an answer at such a short notice..
well the prob here is that i chose a circuit for my electronics project which works on the theory that i have not studied yet. and only 10 days are left for my presentation. so i need loadsa help guys.
all i understand about the functioning of BJTs in the circuit is that the work as switches..either on or off. why? when? how?..i am completely :shock: ..so will need as much info and help as possible...
i will read through the info i get from you guys and try to understand the circuit and the project..
guys i need some serious help people...please help :cry: :cry:


here is the circuit diagram...its a head and tails game..when we connect the battery..either of the leds are on...upon pressing the switch..the leds flicker continuously and when we open the switch...the frequency of the flickering of the leds decreases and eventually one of the leds remain lighted.
the one that is on is due to the base current of the respective BJT.


guys i need alot of info..so please ...................
 

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The circuit runs as an astable multivibrator when the button is depressed. When the button is released and C2 discharges, it finally reverts to a bistable multivibrator. Google these two terms and you might get some insight.
 
Do you understand how bistables and astables work?

The issue here is to make it change from being a bistable when the switch is open to an astable when it is closed.

It may be tricky to make it work since the ratios of R3/R4 and R5/R6 would be critical to success or failure.

I would use an astable followed by a bistable, ie. 4 transistors.
 
ljcox said:
Do you understand how bistables and astables work?

The issue here is to make it change from being a bistable when the switch is open to an astable when it is closed.
Click to expand...
Who, me? :lol:
 


sorry forgot to give these details..

R1, R8 = 470 Ohms
R2, R7 = 1k Ohm
R3, R6 = 10k Ohms
R4, R5 = 3k3 Ohms
C1, C3 = 10 micro-F
C2 = 220 micro-F
TR1, TR2 = C945

does that help you guys giving more info on the circuit??

and no i dont know the terms astables and bistables.
 
Here is a simulation of the schematic. Look at it and tell us what you don't understand. I have a feeling you will say "everything", but a full-text explanation would probably be just as confusing. I encourage you tp do a Google search for "astable multivibrator" and "bistable multivibrator". I saw at least one good text description of how an astable works. The only difference here is the resistors across the timing caps, which causes the multivibrator to lock up in one state or the other when the 220uF cap discharges so low that oscillation ceases.

V2 is just the way S1 is controlled.

BTW, the slight "jaggedness" of the waveforms below is only due to the limited resolution of the plotting software.
 

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Iagree with Ron. You need to understand how an astable and a bistable work before attempting to understand this one.
If you remove R4 & R5 and C1, 2 & 3 you have a bistable.

Alternatively, if you remove R3, 4, 5 & 6 and C2, you have an astable.

Ron, How did you put all the waveforms together?
 
Good advice, Len.

For the waveforms, right-click on the waveform panel, then click "Add Plot Pane". You will notice that there are lots of other useful options there.
 
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