Ac holding circuit

[ash20]

hey guys...
i have a little problem...
i have to make a circuit which can store an analog pulse... so plzz help me with the circuit... i want that the circuit could store the analog pulse for atleast 5-6 seconds and then it goes back to its original state of rest... so that it could again save next pulse after some times....

 

[KMoffett]

Google: sample and hold

Pulse's voltage range? Minimum pulse width?

Ken

 

[Grossel]

I do have a simple circuit diagram for a circuit that can store the peak voltage of a pulse, but I'm not sure if that's what you're looking for.

 

[MikeMl]

What does "AC" have to do with it?

A 555 timer chip monostable would do what you describe, but it would operate on 5 to 15Vdc.

 

[ronsimpson]

hey guys...
i have a little problem...
i have to make a circuit which can store an analog pulse... so plzz help me with the circuit... i want that the circuit could store the analog pulse for atleast 5-6 seconds and then it goes back to its original state of rest... so that it could again save next pulse after some times....

I do not understand! "Store" like digital oscilloscope stores a pulse? Like a tape recorder? "Save"?? "original state"?

 

[ash20]

@KMoffett: well its the output form peizoelectric substance and we are getting maximum 14.4 mv pulse and minimum is 0 v... more pressing could give even more but we have tried only till 14.4 mvolts...

@Grossel: we have to store the maximum voltage (after amplifying it) for some 5-6 seconds so that during that time, we could sound a buzzer...

@MikeMI: well the peizo substance gives a analog pulse with a peak.. we have to store that ... no digital signal could be used... college project... marks deduction on using digital signals... since they are easy to use..

@ronsimpson: well storing means like we record the wave ... like keep it with us for 5-6 seconds... like saving the original state... then we will amplify it and sound a buzzer...

and plzz.... the circuit should also have a mechanism to remove the stored wave after 5-6 seconds so that next time, it could again save next pulse....

 

[crutschow]

Why not amplify the pulse with an op amp and use the amplified pulse to trigger a 555 configured as a one-shot to sound the buzzer?

I don't see any need to store the pulse itself, which makes a more complicated circuit.

 

[Grossel]

Give this circuit a try

I have the circuit for you'r need.

I've inserted a second switch on this drawing. On the original drawing (can't remember where I found it) there was not a switch to the positive opamp input. Because of that, there was a risk that the opamp output where to be shorted through the diode if input voltage was slightly higher than diode forward voltage.

Here it is. Use it wise as I did the job of drawing it for you

 

[ash20]

@crutschow: thats the need of circuit... no digital signals required... store the analog pulse... amplify the stored signal so that it could sound a buzzer... buzzer should buzz after 5-6 seconds (so we have to store till that time)...

@Grossel: hmmm.. thnx for circuit... i will simulate it and tell the results...

 

[ash20]

@Grossel: what is the capacitor value?? and does the storing time depends on product of R and C?? and if yes, then which R?? R1 or R2??

 

[Grossel]

@Grossel: what is the capacitor value??

What is the choosen opamp and how steep will the input pulses become.

and does the storing time depends on product of R and C?? and if yes, then which R?? R1 or R2??

I got the answer, put before I answer, ask yourself - what is the impedance from cap to ground/Vcc through the resistor? Where will the current go (if any).

 

[ash20]

well i will use simple 741 ic and wil use +- 12 v supply...
and as in circuit, there is no direct impedance between cap and ground. isnt it??? and is your capacitor shorting ac pulse to ground?? as is case in voltage divider amplifier tht capacitor in parallel to emitter resistor is used to by pass the signal to ground.. is the case same here also????
i am landing into so much doubts..

 

[Grossel]

Hi. You compare it to a circuit not mention or shown here.

The input impedance of any opamp is near infinite, and wont discharge the cap just like that.

The 741 is an old and slow opamp. If your pulse is of very short duration, the cap might not get full voltage.

Understanding of opamps is a process that can take some time. I recomend you to try figure out some of the basic opamps circuits before dealing with rectifiers and similar circuits.

 

[ash20]

oks.. thanks for help..