# Questions tagged [voltage]

Voltage, otherwise known as electrical potential difference (denoted ∆V and measured in volts) is the difference in electric potential between two points (adapted from Wikipedia). Voltage can be constant (DC) or varying (AC).

4,588 questions
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### High Voltage Capacitor, in a low voltage system?

Quick question, is using a Capacitor rated for High Voltage (lets say 35v) in a System that lets say supplies 5v (like for LEDS.....or what have you) Dangerous? Since it can store UP to 35v, will it ...
2answers
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### computing Impedance related with Voltage Vx

I have a circuit like: How do you get Thevenin ( $V_x = I_x * R$) circuit? I have these formulas, but I am a little stucked... $\ I_0 + Ix = (\frac{V\pi}{r\pi}) + gmV\pi$ ...
2answers
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### Voltage Divider

I need to cut the voltage going through a 1/4" TRS cable (at the connector) by 1/2 (and I need to do this to about 14 cables). I understand that this can be accomplished with two 4.7 kohm resistors ...
4answers
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### if a standard three-phase 400V AC connection is rectified what DC voltage comes out of it?

If a standard (in Europe and a large part of the world except North America and Japan) three-phase 400V AC (three lines having 230V RMS voltage if measured to neutral each) mains supply is rectified ...
2answers
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### How to solve for voltage using node voltage method?

How would you solve for $V_x$ using node voltage method. I can solve this using $Q_{initial}=Q_{final}$, but I can't solve it using node voltage. Using node voltage I get \\$v(t)-v(0)=\frac{k}{170\...
1answer
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### How does a gas grill starter spark work?

On some gas grills, there is a button you push which creates a spark to ignite the gas (propane, natural gas etc.) My questions are probably pretty simple: How does the button create the spark? ...
2answers
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### 5V to 3V, calculate resistor value (or use diode?)

I want to connect this dv motor to the 5V output of an Arduino board. Of course I need to get the 5V down to 3V in order for the motor to function correctly. I've read that I could use a diode with ...
2answers
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### How likely is it that this chip was damaged?

I am trying to use a dataflash memory that requires a voltage of 2.7 to 3.6. Before I was supplying it with too little voltage. Then I supplied it with 5V. Could either of these cause damage to the ...
2answers
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### Understanding operating ranges

I'm trying to understand this table, which specifies the operating ranges for a dataflash memory I am trying to use. The one part that I don't understand is where it says Fr under conditions. What ...
2answers
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### Measuring supply voltage

The documentation for a chip that I'm trying to use says it needs 2.7 to 3.6V. When I use a multimeter and put on probe on Vin and the other on GND I read 1.7V. Is this the correct way to read supply ...
1answer
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### TLC5940 with multiple voltage RGB LEDs

I'm planning to drive multiple RGB LEDs using a TLC5940 with PWM. These LEDs have the following specs: Voltage Red: 1.8V Voltage Green: 3.0V Voltage Blue: 3.3V Current per color: 20mA Common anode ...
3answers
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### Reading and understanding electrical specs on laptop AC adapters

My Dell laptop comes with an AC adapter with the following specs: 65 W Input AC: 100 - 240 V, ~1.5 A, 50 - 60 Hz Output DC: 19.5 V, 3.34 A My HP laptop: ...
10answers
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### What is negative voltage?

Just a general electronics question: What is negative voltage, like -5 Volt? From my basic knowledge, power is generated by electrons wandering from the minus to the plus side of the power source (...
6answers
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### Combining and Charging multiple Lithium Ion Battery Cells (3.6 V or 3.7 Volts)

1] Voltage: 3.6V or 3.7V Are all 18650 lithium ion battery cells 3.6 or 3.7 voltsor or are there different voltage Lithium Ion cells in the market as well? 2] Possible Voltage Shortage? Do all 3.6/3....
2answers
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### Arduino Input/Output Range (Cable Length)

So I have this crazy idea to illuminate a few Christmas lights on the exterior of my house this weekend. I plan on running 2 Cat5e cables about 11.5 meters (~38 feet) from an Arduino board to sensors ...
6answers
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### What is an amp (and other such basic questions) in the simplest possible terms?

I understand that this is a really basic question, but, I've been unable to really understand electrical terminology for some reason. What exactly is an amp? How does it correspond to a watt? And: ...
4answers
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### how to build a low-voltage disconnect switch for DC 12.4V 70A?

How can I make a device that will make the power connected as long as the voltage of the power-supply keeps over 12.4 V (adjustable) and disconnect it if it falls below? It also must connect the ...
3answers
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### Voltage and current in this schematic

I'd like to understand this simple schematic to see if I get things clearly If I understand things correctly: when the switch is open, the current at the right black point is zero, the voltage is ...
4answers
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### Transistor with two voltage levels, Vb ≠ Vcc

Why is my transistor only driving 5V instead of 6V? How can I fix it? I have a 6V, 25mA circuit running some LEDs. I can control them by connecting and disconnecting the positive terminal of the ...
2answers
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### Is it normal for DC wall adapter power supplies to provide voltages above the nominal ones?

When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my 1117CD-5.0 ...
4answers
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### Tolerance of voltage dividers with different values for R1 and R2

If I have two 1k resistors rated at 1% fed by a perfect 10V source then what is the otuput guaranteed to be? 5V ±1% or 5V ±2% or some other value? I can work out this case easily, assume that R1 is ...
1answer
42k views

### How do I measure the voltage coming out of a USB port?

If I attach a USB cable to a USB port, and then strip the wire at the end, then how do I connect a multimeter to it to measure the voltage?
1answer
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### Cheap 500mV reference

For a project, I need a 500mV reference. Some requirements: Relatively low cost. Small size. Preferably surface mount. Supply from 4.8V to 25V. Accuracy ±5% or better Stable over voltage (that is, ...
3answers
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### Best solution to get 3.3V from 5V-20V @ 250mA

For my Super OSD project, I need a +3.3V supply at 250mA from a variable input of 5.5V to 20V. Cost is a concern, as is size. Originally, I considered an LM317 in a SOT-223 package, due to the small ...
3answers
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### Why is it important not to exceed Vcc at the input to a logic gate?

What happens to a logic gate (besides magic smoke discharge) seeing a voltage greater than Vcc? Is it just because the gate was not designed to handle a higher voltage than the recommended Vcc, or is ...
3answers
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### Close enough for voltages?

I want to extend the use of a camera. The camera currently uses a special li-ion 3.7V 1000 mAh battery. I could grab a couple of those batteries, wire them up in parallel, and that'd work just fine. ...
3answers
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### Converting/scaling a voltage range ([0v - 5v] to [-5v - +5v])

Can anyone explain how one would convert one voltage range to another? I'm going to need to convert a range of 0 to +5 volts into a range of -5 to +5 volts. How would this be accomplished? Thanks!
3answers
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### How to I determine/ interpret values of autoranging multimter

I have an autoranging multimeter and many AA batteries.... how do I interpret the readings when deciding to keep or discard AA (1.5 volt) batteries?
5answers
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### How do I read analog devices that produce relatively high voltage?

I found a sensor recently that emits ±90V (AC) on stimulus. How would I go about reading this from an arduino? Update I didn't think there were so many options. :) The kind of thing I'm looking ...
4answers
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### Turn-on voltage for LED

I have a bunch of green LEDs (not super bright), the plastic around the actual LED is physically green, but they did not come with a turn on voltage. 3V seems to work but they're not too bright, is ...
3answers
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### Need help operating a transistor

I have a relay operated by an NPN transistor that needs some voltage applied to the base. I'm working with an arduino and if I give it a digital port, all's well. The circuit looks like this one: ...
2answers
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### PIC voltage measurement

I am running a battery powered device, and would like my microcontroller (PIC) to report on the supply voltage. This is so I can determine how many batteries is used in the supply, and also the state ...
4answers
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### I2C 3.3 to 5.0 V conversion

I'm trying to interface a 3.3V I2C device to a 5V Arduino. I don't have any problem with SCL line. I can use a simple voltage divider but I have an issue with the SDA line as this is bi-directional. ...
3answers
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### Size to power trade off with solar panels

I'm looking to power a remote controlled car with a solar panel on its back. What size to power am I going to get? Is there one light enough that it wont slow the car down?
4answers
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### Bi-Directional Step up and Step down (3.3v <-> 5, etc)

So I've been reading a few threads here and on other forums. I understand there are various solutions for stepping down or up a voltage. What I have found are the LVC series shift regs that give a ...
2answers
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### Distance sensor IR

I am building a distance sensor..I have the ucontroller portion done. I was going to use IR to reflect a beam and get a proportional analog voltage to estimate distance but...it has no range Any ...
5answers
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### Implementing I2C to analog

How can I implement (or maybe there is an IC that already does that) a board whose input would be I2C and output would be analog voltage (0V - 5V) ? Eventually I would like to connect a couple of ...
4answers
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### low voltage motion sensor

I am looking for a motion sensor device that can track person/animal walking by it and record time/date of the event(s). It needs to be able to run on a small battery or two (maybe 2 AA's or a 9 volt)...