Questions tagged [capacitance]

Capacitance is the ability of a body to store an electrical charge

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1answer
288 views

circuit equations derivation problem

I'm trying to derive from scratch the differential equations that characterise Chua's circuit. Here are the ODEs I obtain from that diagram. Current is positive if conventional current goes + → &...
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7answers
17k views

how a phase delay occurs in capacitors/inductors with visual images

Capacitors provide a phase delay between the current and voltage. Current leads the voltage by 90 degree. I was taught these only with the equations. But I want visual intuition, what happens in the ...
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2answers
1k views

Mains Power indicator maximum current draw

I am building a circuit like this: From here. This got me wondering how much current can I draw from a circuit like this? The question would seem to be what is the wattage of an capacitor? Edit: What ...
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1answer
3k views

How do I calculate necessary mosfet turn on/turn off time?

I'm trying to measure capacitance of C1 using this design: Everything works from 3.3V. The mosfets is my addition to it - i want to discharge the capacitor after each half-cycle. Everything works OK ...
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2answers
114 views

Volatile capacitance values at low frequencies

When I measure the capacitance of two cables I get very volatile values if I go to lower frequencies like 500 Hz. The capacitance is about 50 nF. Why does this happen?
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3answers
331 views

going from 5volt 1A to equivalent from a 3V CR2 Battery

I have a small camera with wifi that runs off a 3V CR2 battery. I'm trying to run it from line voltage. Could not find any small transformers that go to 3volt 750mA. I have an Apple transformer for ...
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1answer
1k views

Mimic human capacitance

In a video at Kickstarter a project called Tapcaps is mimicing human capacitance for triggering touches to a capacitive touch screen (the iPhone). At 0:45 in the video we can see a glimpse of the ...
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2answers
2k views

What is the meaning of the nominal frequency specified by manufacturers of crystals?

This answer led to the conclusion that it is unclear what the meaning of the frequency listed by crystal manufacturers actually means. Given this graph on page 79 of this ECS Crystals Application ...
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2answers
635 views

Capacitors in series

Okay so I'm looking at RF designs and I've come across a couple of designs which need 2p2 caps. I've seen C1.C2/C1+C2 being plugged into a function (the tank part of the circuit) which gives a ...
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0answers
302 views

Formulas for Integral Components

Formulas for Integral Components: I am looking for "simple" approximative formulas for integral components. In particular for: A grounded interdigital capacitor (i.e. above a ground plane and with ...
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1answer
2k views

MOS Capacitance and Performance

I was learning about the advantages and challenges in scaling down MOS transistors. I came across this statement in Wikipedia : ...
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2answers
10k views

Why does an ideal capacitor give rise to a rectangular cyclic voltammogram (CV)?

Many scientists are interested in developing supercapacitors, which have electrolyte rather than solid dielectric between the charged plates. In the field of electrochemistry, cyclic voltammetry (CV) ...
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1answer
17k views

How can capacitance values be determined from a cyclic voltammogram?

I am reading an article (Khomenko, Electrochimica Acta 2005, 50, 2499-2506) that investigates the capacitance of carbon-based electrodes for use in supercapacitors. In particular, they use cyclic ...
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1answer
327 views

Measuring capacitance by using two thresholds

I want to measure capacitance using a microcontroller. As there are various drawbacks in measuring capacitor voltage from 0V, this resource has it right by counting the time capacitor charges from one ...
6
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2answers
851 views

How often should I have to set oscilloscope probe's capacitance?

I got a new Owon SDS7102 oscilloscope and I'm using the included oscilloscope probes with it. The manual says that the proper calibration procedure is to let the oscilloscope work at constant ...
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3answers
7k views

I2C extender or repeater?

I am developing a dolly-pan-tilt system, where an Arduino is connected via I2C to three independent rotary encoders for positioning. Having read a few posts on this site and elsewhere, I am aware that ...
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3answers
11k views

Importance of dielectric in a capacitor

We all know that if we put a dielectric inside, the voltage lowers and capacitance increases. Yet, it lowers the energy density. If capacitance increases, then more charge is stored and so its like ...
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2answers
1k views

In general, why do capacitors have a higher tolerance than resistors?

In general, why do capacitors have a higher tolerance than resistors? Capacitors have a tolerance of around 10%-40% while resistors have smaller tolerances generally. Why is that?
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2answers
492 views

What loading capacitor do I use for my crystal?

I am using this crystal (the 7.3728 MHz variant). The datasheet specifies a 5pF to 55pF load capacitance; is this really so? I was under the impression that most quartz crystals had an optimal ...
3
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1answer
944 views

How to make an entire (irregular) surface sense touch with a capacitive sensor?

I'm looking for a way to make a surface touch sensitive. The sensors have to interface with a keyboard encoder to send signals to the computer as keypresses. This is just the way it has to operate. I ...
5
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1answer
226 views

Unwanted capacitance in measurement setup - what to consider?

I have a current measurement setup (which supposed to measure < 1nA). It has 20 channels and switched using a relay matrix. Using a LCR meter I measured for one channel (In the schematic below, ...
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2answers
3k views

How to measure/compensate wire's stray capacitance

How should one measure and compensate (If necessary) a wire's stray capacitance in low-level measurements? Is Guarding applicable here? If so, does it mean having a wire with same signal voltage ...
4
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3answers
3k views

Load capacitance for RTC Crystal

I'm working with an LPC2387 (datasheet), and pp. 55-56 of the datasheet specifies several options for the RTC crystal with different load capacitance: 11pf, 13pf, and 15pf. For each of these crystals, ...
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2answers
2k views

Effect of parasitic capacitance on an ideal signal?

How does parasitic capacitance affect an ideal signal? Ie. We have an ideal signal shown below, what would it look like with parasitic capacitance accounted for?
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3answers
12k views

Reading very low capacitances with Arduino

I'm trying to measure the capacitance of a very low capacitance sensor (two parallel plates across a block of foam). This is a self-produced force sensor; I'm trying to eventually use some of the work ...
10
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5answers
69k views

Why does the distance between the plates of a capacitor affect its capacitance?

Why does the capacitance of a capacitor increase when its plates are closer in distance to each other?
3
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1answer
243 views

Diffusion capacitance approximation for bipolar power transistor

I'm trying to remember the approximation for the value of the diffusion capacitance for a bipolar power transistor. I think it might have been gm/Ft? Can anyone confirm this and/or give a reference? ...
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3answers
10k views

How does a Theremin “antenna” work?

I always assumed that the shape of the antennas was important; a vertical monopole for pitch and a horizontal loop for volume, thinking that this minimized their interference with each other. But it ...
4
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2answers
12k views

Trace-to-plane capacitance?

I'm routing some traces which carry high speed UART at 1.8432 Mbaud. The traces will be routed on the same layer as a power or ground plane (because it's a 2-layer design.) This will introduce ...
39
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11answers
4k views

Is there a dual of the transformer?

Capacitors and inductors are duals of each other. A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?) Also, you can vary ...
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2answers
1k views

How do I choose the correct capacitors to use with my Crystal?

I am looking at using this crystal for a new circuit design. It will provide the main oscillator for my PIC application. Here is the part on digikey. The datasheet indicates that it has a load ...
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3answers
1k views

µ in the Middle of a Capacitor Rating

I'm looking at an electrolytic capacitor (and old blue, Philips one used in electronics classes) and am wondering why it is printed with 4µ7-M. I tried Googling, figuring that it was a common enough ...
21
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4answers
10k views

Crystals and load capacitance

If a crystal has a rated load capacitance of 6 pF, is the right thing to do to put a 6 pF capacitor to GND on either leg of the crystal? I'm using it as the clock source (TOSC) for an XMEGA and it's ...
6
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2answers
2k views

Transmission Line and capacitive effect

I am driving a digital pin with a 10Mhz signal. At the pin, the signal's rise time is slewed to 35us such that the signal is no longer a pulse but a triangular waveform that does not reach the full ...
27
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10answers
37k views

What are some reasons to connect capacitors in series?

Usually you either combine capacitors in parallel because you want to increase the total capacitance while fitting the components in a certain shape/position, or you just combine capacitors by buying ...
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6answers
2k views

Capacitive Sensing

Is there a way that I can make an Arduino or other Micro-controller detect a change in capacitance? I'm thinking of having a screen on my door that only turns on when you touch the metal door handle.

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