# Help me! Urgent!

Discussion in 'Homework Help' started by govinda, Sep 1, 2013.

1. ### govinda Thread Starter New Member

Sep 1, 2013
3
0
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

2. ### WBahn Moderator

Mar 31, 2012
18,088
4,917
Why are you trying to do this in the first place?

Is it a school project/assignment? If so, what are the constraints? What components are you (2) allowed to use, (2) must use, and (3) can't use.

What are your requirements? Just saying you want to measure the charging time of a capacitor isn't giving us very much. The what kind of capacitances are you looking to measure? There is a world of difference between working with a 5pF and a 5mF cap. What kind of resolution, accuracy, precision do you need to achieve.

How are you going to get your data? Are you using a microcontroller? Which one?

3. ### govinda Thread Starter New Member

Sep 1, 2013
3
0
school project
10uf capacitor
components which are commonly used

Apr 5, 2008
15,806
2,389
5. ### govinda Thread Starter New Member

Sep 1, 2013
3
0
I know the theory behind it
I want to make a circuit such that when we attach a capacitor to it will directly display its charging time

Apr 5, 2008
15,806
2,389
Hello,

You could have a look at the 555 in monostable use:
Next Submission, 555 Monostable

This circuit will give a pulse dependend on the capacitor value.

It is upto you HOW to measure the pulse lenght.

Bertus

7. ### wayneh Expert

Sep 9, 2010
12,392
3,246
Requiring a dedicated display adds a LOT to the complexity to your project.

Otherwise I like your idea of using a comparator. I would add to that idea and use a window comparator. Then you could precisely time the interval required to charge from the low reference voltage up to the high reference. The comparator could start and stop a timer. If I was doing this, I'd use a pre-made timer.

Now that I think about it, there are a lot of ways to tackle your task. You are essentially measuring the capacitance. I think AC methods would be superior to a single DC timing.

8. ### Bernard AAC Fanatic!

Aug 7, 2008
4,240
414
Use constant current supply [ 24v supply & 1 meg resistor ] stop watch & volt meter. Charge C to 10 V & measure time. Sub. comparator, V ref, pulse gen. counter & gates for eyeball & stop watch.

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