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I have a simple circuit that controls a 5vdc power source. My question is; how do I know what the Potential Difference is? In the circuit below I am sending 5v DC to a component (dotted box is where the capacitor will go).

Edit: Not sure why this was voted down twice. Its a question. Some people are too easy to vote down on http://electronics.stackexchange.com. Shouldn't be this way.

enter image description here

PhillyNJ
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    Huh? Potential difference *where*? What are you trying to accomplish? *It is difficult to tell what is being asked here*. – Olin Lathrop Mar 12 '13 at 12:58
  • Potential difference = voltage between two points, but which two points? Why are you putting a capacitor there? – pjc50 Mar 12 '13 at 12:59
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    Why do you think it would be anything other than 5V? – Dave Tweed Mar 12 '13 at 13:12
  • This is my thought which can be wrong; since power can be switched on and off to the component, there might be some flutter – PhillyNJ Mar 12 '13 at 13:18

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To know the potential difference across a capacitor, you also need to consider what is happening as a function of time. This is what makes a capacitor useful. If you apply a DC voltage to a capacitor, the potential difference across the capacitor will be that DC voltage.

If that voltage changes, then a current will flow with the aim of making the capacitor voltage the same as the applied voltage. Ideally, this current has no limit, and the voltages are always identical, but in practice there is some series resistance, even if only the non-ideal resistance of the wires and the capacitor, that limits the current and introduces a difference.

The magnitude of the current that will flow (ideally) is a function of the rate of change of voltage, and the capacitance:

\$ I = C\dfrac{dV(t)}{dt} \$

As others have said, it's unclear what you are trying to accomplish or what you are asking, so it's difficult to more directly answer your question.

Phil Frost
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  • Hi - Thanks for the help. I am learning so bare with me :) - When I supply the 5vdc to the component, I want to make sure that it is 5v, no more or no less. Like I said I am learning... – PhillyNJ Mar 12 '13 at 13:40
  • @PhilVallone it's still hard to know what you are asking about. What component? How are you supplying 5V? What does a capacitor have to do with all this? I can't really read your schematic, and it's not arranged in a readable way. See http://electronics.stackexchange.com/questions/28251/rules-and-guidelines-for-drawing-good-schematics and please try to reduce your problem to a more simple circuit. – Phil Frost Mar 12 '13 at 14:11
  • I'll read the link you provided Thx - To answer your question of which component; the component marked ATTiny 84 (which is a chip) will supply the Raspberry Pi (Computer) 5v DV when requested. When the 5v is sent to the Raspberry Pi, do I need a capacitor between the 2 components to ensure the current is 5v with no flutter? – PhillyNJ Mar 12 '13 at 14:32
  • @PhilVallone, Volts are used to measure potential. Amps are used to measure current. It sounds like you are just starting out in electronics, and you are still learning the very basics like this. Reading a site like allaboutcircuits.com might be very helpful bringing you up to the point where you "know what questions to ask". – The Photon Mar 12 '13 at 14:49
  • @PhilVallone it sounds like the question you want to ask is "how do I stabilize a voltage with a capacitor?", and the problem here is you don't understand how capacitors work. It really has nothing to do with ATTiny or Raspberry Pi. That's different enough from this question that I'd suggest asking a new one. Try to put a point on the fundamentals you don't understand, and then you will get good answers that you can apply to problems like this. – Phil Frost Mar 12 '13 at 15:26
  • @PhilFrost - Thx - will do – PhillyNJ Mar 12 '13 at 15:48