# Questions tagged [capacitance]

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

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### Easiest way to detect objects using DIY materials

I want to build a Scrabble board that detects tiles placed, mainly as a one off challenge and learning experience (i.e. not a commerical product). I haven't started building yet: I'm trying to work ...
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### What is the difference between capacitive liquid level sensor and potentiometer liquid level sensor

I have a sensor I use to determine the level of water in my swimming pool. One person has told me it is a capacitive sensor and another said it works like a potentiometer. I would like to know what ...
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### When increasing the frequency of an induction motor can't I just add a capacitor to maintain torque instead of increasing the voltage?

When increasing the speed of an induction motor if one wants to maintain the same torque, the voltage has to be increased at the same proportion as the frequency of the AC supply. This is because the ...
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### Find R value from capcitor discharge plot obtained using scope

I'm using an oscilloscope with probes that are specified to have to have an input resistance of 10Mohms, I apply 5 volts (using power supply) in parallel to my capacitor and use the scope in parallel ...
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### Micro switch capacitance on the inverting input pin of operational amplifier

I want to use a microswitch on the inverting pin of my transimpedance amplifier to be able to select two different channel of my transducer as follow: It the microswitch datasheet in is mentioned ...
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1 vote
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### Role of the load resistors in an astable multivibrator

I am currently trying to wrap my head around astable multivibrators. I want to design a circuit that oscilates at about 1 kHz. The formula I am using to determine the values for the base resistors (I ...
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### Vary Capacitance

I'd like to vary two identical capacitors that are connected in parallel and sinusoidally varied with a 180 degree phase shift, i.e. so CT is constant. The actual value of capacitance isn't too ...
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### Input capacitance estimation for a buck converter

To estimate minimum input capacitance required for a buck converter to help with power stability & noise suppression, I came across below equation by TI. https://www.ti.com/lit/an/slyt670/slyt670....
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### Adding a capacitor to the output of an op-amp can cause instability? (PCB trace capacitance)

In my amplifier design, I checked all the possible issue for finding the instability problem in my previous post: Transimpedance amplifier with OPA838 - oscillation - supply voltage , Transimpedance ...
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### Do batteries have capacitance?

I have a couple of old car battery chargers that use a center tapped transformer and two diodes as a full wave rectifier. There is no smoothing capacitor, so without a battery attached I get the ...
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### 100mF Tantalum Capacitor?

I was looking at a circuit online when happen that both in schematic and on the board I saw this tantalum capacitor with a value of 100mF. Now 100mF are 100000uF, It looks small for having such a ...
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### Detecting when a barbell touches a person's chest [closed]

I am trying to detect the moment when an Olympic barbell touches a person's chest during bench press. I have been trying to detect a change in capacitance to do this. The problem is the person's hands ...
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### Is my rough design of wireless powered leds with a capacitance touch sensor reasonable?

Disclaimer: I am not an engineer, but I have a background in physics, so theoretically I should know most of this stuff, but in reality, I might have made some very basic and dumb mistakes. The ...
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### Measure capacitance with Arduino and AD7746

I want to measure capacitance with an Arduino and an AD7746 capacitive sensor. I already used ChatGPT and some examples, but the sensor measures just 0 pF. When I measure with an LCR meter, the ...
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### How to connect an electrode to ground?

I have an array of 16 electrodes that I want to be disconnected from everything until selected and then connected to ground, one at a time. Would a multiplexer work for this? My application is sensing ...
1 vote
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### PSC motor auxiliary winding current at full speed

In articles, e.g. here, I often find this statement: In an auxiliary winding, a counter EMF is produced as the speed of the motor increases, and this EMF will limit the current that passes through ...
1k views

### Is it possible to do water detection with a single electrode?

I need to detect the presence of water, but there is a catch. I can only have one single electrode contacting/submerged in water. It is in a mini-tank made of plastic (for a handheld device) so I ...
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1 vote
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### Electrical modeling of multilayer structure

If I have a construction of layers wherein the topmost layer is conductive, followed by two different insulation materials in between, and a bottom structural layer that is a partially conductive ...
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### Capacitance displacement probe guard ring circuitry

I am attempting to build my own capacitance probe for high precision displacement measurements. The working principle is simple - a constant current AC signal (~100kHz) is passed through the probe ...
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### How to Build Durable, DIY Capacitive Sliders for a Custom Macro Pad?

I'm working on a custom macro pad project and I'm planning to include three 50mm long sliders. I'm leaning towards capacitive sliders due to their suitability for my design, but I'm flexible on the ...
129 views

### Where to place the capacitor when modelling a single long wire?

Consider a high-voltage power line that is hundreds of kilometers long. Such a wire has a capacitance, inductance and resistance. This answer to a previous similar question contains the following ...
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### Low LDO output capacitance (stability)

I need to replace the REG104 LDO (End of life) in a circuit where the max. allowed LDO output capacitance is 100 nF because of explosion proof intrinsic safety requirements. The REG104 LDO is stable ...
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### A circuit to detect AC and DC voltage from a source

I am looking for a circuit that determines whether the input signal is AC or DC. For example, if the AC voltage is connected, the red LED will turn on, and if the DC voltage is connected, the green ...
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### Why are MOSFETs called voltage controlled devices even though we have to push in charge/current to charge the input capacitances?

I was wondering why MOSFETs are called voltage controlled devices when the input capacitances of the MOSFET (Cgd and Cgs) need to be charged in order to turn ON. Wouldn't that mean that they are ...
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### Capacitance equation understanding

Does anyone know where the bottom equation is derived from? Why is it 8V/9V? Source: Mouser - Everything for Capacitive Power Supplies by TDK
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### Why do inductors and capacitors cause phase shifts between current and voltage? [closed]

I am learning about grid level stabilization services. My native language is German and I am translating the specific terminology. If I use the English terms incorrectly please edit my below sentences....
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### What is the purpose of these capacitors connected directly to the OpAmp output?

I am studying this schematic and I come across the following section: As can shown capacitors are connected directly between the Op-Amp output to the supply (5V). What is the purpose of these ...
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### Relation between rise and fall times and capacitance

So I'm currently reading the datasheet of the Motorola 68hc000 CPU and I want to be able to estimate how many devices I can plug to the bus directly before I encounter issues. So first things first, ...
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### What capacitance would I need to actuate a solenoid?

I have a project that requires I hit a 5 cm ball with a push-pull solenoid. For the purposes of the project the solenoid needs to be actuated using a capacitor, but after reading multiple forums, I am ...
230 views

### Why does the air gap between the electrode and the overlay of a capacitive sensor have a negative impact on the touch performance?

I see in the design guidelines that the airgaps between the electrodes and the overlay of the capacitive sensor have detrimental effect on the performance of the touch sensor and they should be filled ...
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### Capacitors on USB data lines for better USB data blocker

USB data blockers are small adapters that have a male and female USB connector, but inside the data lines are disconnected. They can be used to safely charge your devices on public USB ports without ...
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### Capacitance measurement mode on the multimeter

I have one more question related to my cheap Aneng SZ08 multimeter, which I've purchased recently and am discovering its capabilities. This question is related to the capacitance measurement mode. To ...
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### Why +ve charge(conventional current) flows out of the -ve terminal of a battery?

Please consider question 45 part c. In this question if I consider that the capacitor after being fully charged at 24V is now connected to a 12V battery, and since some heat will be lost as charge ...
1 vote
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### How should I choose TVS diode capacitance for my 2MHz RS-422 application?

I have been looking at which TVS diode to select for a protecting a set of RS-422 driver lines, however I am struggling to understand how to choose them based on the diode capacitance. The signal will ...
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### What is the step by step mechanism for charge to accumulate on the capacitors of this circuit?

In this circuit, what will initiate the charge to flow from the batteries to the capacitors? I would like to know how is sufficient potential difference created in this circuit to allow for the ...
1 vote
260 views

### Reducing EMI with ground plane

I came across this post on how to reduce EMI in a PCB. From this, I learned that there actually exist two types of current. The first is the conductive current (the current that flows through a ...
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1 vote
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### Crystal oscillator load capacitance voltage rating

I am using this crystal oscillator in my design.I know how to calculate the load capacitor. The XTAL is connected to this microprocessor. May I know how to select the voltage rating of the load ...
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### Selection of RC values based on application - How?

Please see the below connections: I have seen long back another board and chassis ground connection with an RC with a different set of RC values. I read that the capacitor is there to build a low-...
1 vote
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### Understanding CLoad of a gate driver and the Cgate of an SiC MOSFET

I have selected an SiC MOSFET (UJ3C120040K3S) for my pulsed power application. My rise and fall time requirements are both 20 nS. My gate drive voltage will be 15 V. Based on the total gate charge ...
1 vote
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### PN junction capacitance and varactor diodes

I do know that a PN junction when expanded for a diode when in reverse biase will cause that diode to act like a capacitor, but what sets the varactor diode apart from other diodes?
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### Simulate or Calculate Inductor Flyback Voltage from Component Parameters?

simulate this circuit – Schematic created using CircuitLab Top circuit can be used to simulate the increase in velocity of the JATO Powered Chevy featured in the first episode (and subsequent ...
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### How to test the working of a decoupling capacitor with an oscilloscope?

How can we test the working of a decoupling capacitor with an oscilloscope. I think I understood the need for a decoupling capacitor in a circuit. One of their use is to remove the noise from the ...
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### Why do we need multiple capacitors in parallel instead of a single equivalent capacitor? [duplicate]

I am trying to read and understand the below Raspberry Pi schematic to validate some of the basics I learned recently regarding passive components and how they are used in real schematics. When I ...
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### A 555 timer changes time when you touch it?

I designed a simple 555 astable 50% duty cycle square wave generator, assembled in China on SMT PCB. It works well: Except when you touch it, or even put your fingers near it, the timing changes ...
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### 3 phase motor in Steinmetz connection on a single phase supply direction change problem

I want to run a 3 phase induction motor on a single phase power supply. I'm aware of the low operating power & low starting torque in this configuration. My load & duty cycles are also not big,...
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### How can I find the steady state of current I with sinusoidal voltage source?

I am reading the book Electric Circuits 10th Edition from Nilsson and Riedel. In page 321 has a problem that seems easy but I find a difficulty to solve it.The problem states: A 90 ohm resistor, a 32 ...
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### Online measurement of capacitance of open-load AC cable

I would like to detect whether a three-conductor (L1, N, GND) AC cable's length has been increased – for example, when a connector with attached cable is inserted into a standard/unmodified connector. ...
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### Derive a State-Space Model for an Electric Circuit with three Energy Storage Components

I want to model the shown circuit diagram with a state-space model. However, I cant solve it since I obtain four unknown variables while only three of the derived equations are linear independent. ...
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