IC 555

[(*steve*)]

It looks to me like the inputs to the comparators are exactly the wrong way around in that diagram.

Compare it with this one:

 

[vick5821]

It looks to me like the inputs to the comparators are exactly the wrong way around in that diagram.

Compare it with this one:

So the diagram is wrong ?
How about the explnation for the diagram abt IC 555 working principle : http://www.circuitstoday.com/555-timer#working-principle??? I hope I didnt get a wrong diagram and explnation.I will be so confuse because I am not sure which block diagram for IC 555 is correct >< @@@

 

[(*steve*)]

Explanation looks right, diagram looks wrong.

Check other diagrams for yourself.

Some others show a circle on the input. This stands for inverting or "-" input on the comparator.

 

[vick5821]

Explanation looks right, diagram looks wrong.

Check other diagrams for yourself.

Some others show a circle on the input. This stands for inverting or "-" input on the comparator.

Is it like this ? Got a circle on the input..So it actually means the same ? positive top and negative below ?
http://www.williamson-labs.com/555-tutorial.htm

 

[Rleo6965]

@Rleo6965,

Is this the correct block diagram for IC 555 ?
why the comparator the positive terminal is at bottom ?

Referring to above diagram.

- and + input terminal was drawn in such a way that input lines will not cross other line for clarity.

 

[vick5821]

Referring to above diagram.

- and + input terminal was drawn in such a way that input lines will not cross other line for clarity.

So the diagram is correct ? But suppose the 2/3Vs is located at negative side of the comparator ?

 

[(*steve*)]

Referring to above diagram.

- and + input terminal was drawn in such a way that input lines will not cross other line for clarity.

Except they have the Trigger connected to the non-inverting input of one comparator, and the threshold connected to the inverting input of the other comparator

 

[Rleo6965]

Why they connect the output of IC1 to control voltage pin of IC2 ?

This to increase and decrease threshold voltage 2/3 vcc or 8V ( +12V VCC ). If pin 5 control voltage pulled down by 10k resistor. This result higher frequency output of 2nd timer. If control voltage goes higher or 10k resistor was pullup to high voltage. Output of 2nd timer will be at lower frequency. Since control pin signal from astable Timer 1 was low oscillator. Output of timer 2 will short high frequency and short low frequency or similar to warble sound on the speaker..

why they use a diode for IC1 ? To achieve 50% duty cycle ?

If diode was not connected to R2. Charging time will be longer because of total resistance of R1 and R2 charging the capacitor. Discharging time of the capacitor will be shorter because discharging path will only in R2 that that connected to discharge pin 7. So duty cycle of long high pulse and shorter low pulse result. Not 50%.

Now if diode was connected in forward bias in R2. Charging path would be R1 and current bypassing R2 ( because its in forward bias ) to capacitor and discharging would be capacitor to R2 to pin 7. Since R1 and R2 are same value of 68K. A duty cycle of 50% result output.

 

[vick5821]

Except they have the Trigger connected to the non-inverting input of one comparator, and the threshold connected to the inverting input of the other comparator

I do not understand this!

inverting input is -
non-inverting input is '+' ?

and trigger connected to inverting ? thershold connected to non-inverting ?

 

[Rleo6965]

I do not understand this!

inverting input is -
non-inverting input is '+' ?

and trigger connected to inverting ? thershold connected to non-inverting ?

He he he.

I hope , I can explain this properly.

High signal in Inverting input will result low output signal. So it invert signal.

High signal in Non-inverting input will result High output signal. No inversion of signal.

 

[vick5821]

He he he.

I hope , I can explain this properly.

High signal in Inverting input will result low output signal. So it invert signal.

High signal in Non-inverting input will result High output signal. No inversion of signal.

What are you trying to say ? what relationship exist ? I know your facts are logical but I do not know how it being applied
What I meant is inverting input is the negative side in the comparator and non-inverting input is the positive side of the comparator and this contradicts with that steve said ?

trigger input is connected to '+' or '-' of the comparator? I am so confuse now for different kind of information available!

 

[Rleo6965]

Except they have the Trigger connected to the non-inverting input of one comparator, and the threshold connected to the inverting input of the other comparator

Yes. wrong label of + - comparator. I hope they correct it.

 

[Rleo6965]

What are you trying to say ? what relationship exist ? I know your facts are logical but I do not know how it being applied
What I meant is inverting input is the negative side in the comparator and non-inverting input is the positive side of the comparator and this contradicts with that steve said ?

trigger input is connected to '+' or '-' of the comparator? I am so confuse now for different kind of information available!

I suggest you google for opamp and comparator and this will help you understand.

 

[vick5821]

Yes. wrong label of + - comparator. I hope they correct it.

so, dun refer to the block diagram I posted ? refer to the block diagram posted by steve ?

Correct ?

 

[Rleo6965]

so, dun refer to the block diagram I posted ? refer to the block diagram posted by steve ?

Correct ?

Yes.

Just to inform you. " - " and " + " in comparator was referring as input only not + side supply voltage or - ground side terminal.

 

[vick5821]

I know that..it determines the output from the comparator..if the + input is more positive than the - input, the output is Vs or HIGH

So, the sign is important

Am I correct ??

Hehehe

 

[Rleo6965]

I know that..it determines the output from the comparator..if the + input is more positive than the - input, the output is Vs or HIGH

So, the sign is important

Am I correct ??

Hehehe

Yes correct.

i'm starting to have headache now.

 

[vick5821]

Hahaha..sorry I will look back on what you all have explained to me..I think I learnt alot from here

Thanks

 

[vick5821]

This to increase and decrease threshold voltage 2/3 vcc or 8V ( +12V VCC ). If pin 5 control voltage pulled down by 10k resistor. This result higher frequency output of 2nd timer. If control voltage goes higher or 10k resistor was pullup to high voltage. Output of 2nd timer will be at lower frequency. Since control pin signal from astable Timer 1 was low oscillator. Output of timer 2 will short high frequency and short low frequency or similar to warble sound on the speaker..

What does this two means ?

 

[(*steve*)]

I know that..it determines the output from the comparator..if the + input is more positive than the - input, the output is Vs or HIGH

Kinda.

An increasing voltage on the + (non inverting) input tends to force the output high.

And increasing voltage on the - (inverting) input tends to force the output low.

For comparators only the difference in voltage matters, for op-amps, the difference in phase relationship between the inputs is used for other purposes.