Help me! Charging time of capacitor circuit?

[govinda]

I need to develop a circuit to measure charging time of capacitor
I am kind of less in practical knowledge (this is my first project)
So far I have thought of giving a reference input and capacitor voltage to comparator
then there is counter that will count the number of time it will go high
then the time divided by the no. of times it will go high will give me the charging time that will be displayed on LCD
Is this method Okay? Will it work?

Can any one please draw me a detailed circuit daigram
for the same PLEASE!!!

[Bored@Work]

So when is that homework due?

[BravoV]

Let me guess, from India ?   

[hlavac]

Charging time can not be measured, rate of charging depends on voltage applied (or rather current into capacitor) and existing charge in capacitor, and even so technically it takes infinite time for the cap to reach the voltage applied.
Not mentioning the dielectric memory effect that further screws things up.

Now go get me that left handed screwdriver will you?

[abhaymv]

Let me guess, from India ?   

Ah... come on. Please don't stereotype.

[SeanB]

Can't be from ZA, school leavers here are unable to write in English, but they can do other assorted skills, none involving literacy in either any language or maths or science.

[PA4TIM]

I think he thinks India because of this: http://www.edaboard.com/thread297668.html  there are many people from India there and his nick sound like India. But what does that matter ?

You need to develop ? You mean like for school ?

 Originally Posted by govindaAF

So far I have thought of giving a reference input and capacitor voltage to comparator
then there is counter that will count the number of time it will go high
then the time divided by the no. of times it will go high will give me the charging time

Why you want to measure that time ? ( for instance if it is for school it is just the principle, if this is to measure the capacitance of a capacitor the circuit must be made more carefull. If it is some sample/hold thing you need a very low leakage capacitor )
Your idea can work. You need a resistor to limit the current and this depends on the capacitor. A 10F supercap charging through 10M can take a while and 10pF with 10 Ohm will go way to fast. The resistor value gives you resolution (in the analog part of the schematic)

One thing, I think you just wrote it a bit strange because now it looks like you want to count the number of times the comparator gets high and that is just one time. If the comparator inputs are equal the comparator fires. And that is when the charge voltage is equal to the reference voltage.

So you monitor the comparator while the microprocessor counts its clock (or so, I'm not into digital). Then you must calculate how mucgh time one cycle takes and multiply that number times the number of counts.
 

[c4757p]

Charging time can not be measured, rate of charging depends on voltage applied (or rather current into capacitor) and existing charge in capacitor, and even so technically it takes infinite time for the cap to reach the voltage applied.

I don't think he's confused and wants to measure the "charging time" like it's a property of the cap. I think it's charging from some external current and he wants to know how long it takes.

I need to develop a circuit to measure charging time of capacitor
I am kind of less in practical knowledge (this is my first project)
So far I have thought of giving a reference input and capacitor voltage to comparator
then there is counter that will count the number of time it will go high
then the time divided by the no. of times it will go high will give me the charging time that will be displayed on LCD
Is this method Okay? Will it work?

Sounds good to me. I assume you're using some sort of microcontroller. Make yourself a cup of coffee and have some intimate time with the timer documentation for that MCU. It should be quite easy to count how long the comparator output is high.

Can any one please draw me a detailed circuit daigram
for the same PLEASE!!!

Want to know my hourly rate?

[PA4TIM]

Want to know my hourly rate?

[c4757p]

I think he thinks India because of this: http://www.edaboard.com/thread297668.html  there are many people from India there and his nick sound like India. But what does that matter ?

Oh dear lord, it's a copy-paste.

Dude, if you expect anybody to take the time to help you, you need to show some respect and take the time to participate in return. That means you don't register on every electronics forum you can find and paste the same plea to all of them, go away for a while, then come back to scrape up your answers. A forum is a place for people to talk, not a free design service for you.

[BravoV]

I guess PA4TIM understands me well ! 

Oh dear lord, it's a copy-paste.

Dude, if you expect anybody to take the time to help you, you need to show some respect and take the time to participate in return. That means you don't register on every electronics forum you can find and paste the same plea to all of them, go away for a while, then come back to scrape up your answers. A forum is a place for people to talk, not a free design service for you.

Looks like you don't hang out often at other popular electronic forums like edaboard or electro-tech and etc. These kinda scenes are norm.    I guess its probably cultural thing, so get use to it.

Typical signatures that are easy to spot, usually 1st post, weird unnecessary character attributes like bold, big font or lots of capitals and sometimes eye catchy weird colored font, and also watch for very insisting words like ... "PLEASE !!" , "URGENT !!" , "NEED HELP !!!"  and etc . 

A fine example from recent locked thread -> Here , there are many other examples here as well, but currently here this forum does not have these type of thread as many as edaboard or electro-tech, I guess its just the matter of time.

Sorry, just can't help it, its just I've seen too many-many examples (maybe PA4TIM too) at various forums for years, that its almost unbearable not to come out with this kind of conclusion. 

[c4757p]

Well yeah, I kind of figured it was. Didn't want to accuse him since I didn't know where else it came from and couldn't be bothered to look.

[IanB]

Two reasons for thinking the poster is from India: (1) the name, "govinda"; (2) the phrasing, "for the same". The use of "the same" is very characteristic of the English spoken in that part of the world.

[Stonent]

Let me guess, from India ?   

 

Ok so I wasn't the only one.

[PA4TIM]

A fine example from recent locked thread -> Here , there are many other examples here as well, but currently here this forum does not have these type of thread as many as edaboard or electro-tech, I guess its just the matter of time.

I think I know who that is too : http://www.edaboard.com/thread297059.html Same use of abbriviations and language, started half a dozen topics there about an energy meter. Does not have a clue about electronics. Also from India

[Mki]

Typical signatures that are easy to spot, usually 1st post, weird unnecessary character attributes like bold, big font or lots of capitals and sometimes eye catchy weird colored font, and also watch for very insisting words like ... "PLEASE !!" , "URGENT !!" , "NEED HELP !!!"  and etc . 

Sorry for continuing this, but this is like kind of a 419 scam for electronics  Also, it's a sign that some critical mass of popularity is reached in forum and it starts to attract these types of future engineers.

[Stonent]

As I had mentioned in a previous thread I've seen this a lot and at the time I said from a particular part of the world, but wasn't specific. This may be a confirmation.

Anyway what I have seen at least in the PC/IT world is that there seem to be guys in the general India area who end up taking a job that quickly puts them in over their heads and then post these HELP!!! style messages on internet message boards.

I've even seen them say things like they got a job to build a website and don't know the first thing about web design so can someone step by step tell them how to set it up, interface it with a database, configure several things etc.

I don't know why this is, may be a cultural thing?  I once worked with a guy from Bangladesh and in his explanation there are a lot of "momma's boys" created as part of the culture (i.e. living with parents until married and mom cleans up after them constantly etc) where they are built up in such high esteem that they think they can do anything but quickly find out that in the real world they can't function because they are not self sufficient.

Anyway, that's his explanation of it.

[jasonbrent]

As far as this thread goes, I learned about the existence of edaboard from it. So I give it 2 thumbs. one up, one down. 

-jbl