Questions tagged [electrical-engineering]

Study and applications of electricity, electronics, and electromagnetism. Use this tag when someone who has trained as an electrical engineer is likely to be able to answer your question.

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Why do color TVs make black and white snow?

If you let a color TV display something from an unplugged display port, it displays snow, right? Randomly varying black or white pixels on the whole screen. My guess was that the television was ...
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56 votes
4 answers
36k views

Why is kVA not the same as kW?

I thought my electric car charging unit uses 6.6 kW of power. However, I found the label and it actually says 6.6 kVA. When I saw this I thought something along the lines of... Well, $ P=...
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53 votes
9 answers
21k views

Why do cars have mirrors for rear view rather than cameras?

Despite having so much technological advancement, I wonder why cars still uses mirrors (right and left side of the driver) for the rear view. These mirrors can be easily replaced by cameras and ...
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45 votes
9 answers
7k views

My customer wants to use my products to do something unsafe. What is my ethical obligation?

We sell products that attach to a motor drive's DC bus. We also formerly sold diode kits that let you hook one product up to multiple drives. We stopped selling those diode kits because they were ...
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29 votes
3 answers
6k views

Why are two wires used in railway overhead equipment?

While watching the train videos, I came across these overhead wires. After searching on the internet, I found that both catenary and contact wires carry the same voltage and are connected by vertical ...
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25 votes
3 answers
102k views

Calculating pitch, yaw, and roll from mag, acc, and gyro data

I have an Arduino board with a 9 degree of freedom sensor, from which I must determine the pitch, yaw, and roll of the board. Here is an example of one set of data from the 9-DOF sensor: ...
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23 votes
2 answers
9k views

Why doesn't a lightning strike destroy the lightning rod?

Lightning strikes have been known to cause massive amounts of damage. The stats on a lightning bolt are: current levels sometimes in excess of 400 kA, temperatures to 50,000 degrees F., and speeds ...
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21 votes
4 answers
29k views

Would it make sense to have a 12V lighting circuit in a house?

Modern LED bulbs must convert the standard household supply (for example $240\text{V AC}$ in the UK) into a DC supply at a lower voltage (usually $12\text{V DC}$ I think) for the LED array. This is ...
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18 votes
3 answers
15k views

How does a traffic light sense the proximity of vehicles?

Some traffic lights don't operate periodically but instead detect when a car is close by and then turns green. I have heard that they use a magnetic sensor embedded in the road to sense cars as they ...
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17 votes
4 answers
8k views

Why does the microwave plate start in a random direction?

...or what type of motor is used there? I found this type of motor - usually powered with low-voltage AC (~12V), but at times with 230V, in several appliances that require very slow rotation and ...
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16 votes
1 answer
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What is it about the cabin electrical supply on cruise ships that makes surge protectors dangerous?

Surge protectors are banned on cruise ships, and so are confiscated during boarding. Extension cords and cube taps etc. are discouraged, but not banned. I'm asking specifically about surge protector ...
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15 votes
2 answers
3k views

What is this small rotating part from a cell phone?

What is this tiny rotating piece of hardware that I found inside my Samsung GE1202? It has E9C written in blue on it.
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15 votes
2 answers
6k views

Quantifying inertia on the electricity grid

A lot of discussion about the modernisation of electricity systems is about "inertia". This is usually a qualitative discussion about how turbines (in hydro, coal & gas plants) with lots of ...
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14 votes
3 answers
6k views

Can I use a ultrasound sensor to measure water level?

If I use an ultrasonic sensor will it detect the water level? I was thinking about a product to read water level on water boxes (common in Brazil). I researched about instrumentation for this ...
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14 votes
1 answer
733 views

What limits a power plant's load gradient?

Each power plant has a load gradient characteristic, describing to what extent it can change the output of its generators in a given timeframe. Reading the literature, I know that, for example, a gas ...
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13 votes
2 answers
316 views

Do "analog FPGAs" exist?

I am thinking on analog circuits, whose circuit design could be read (or, at least, significantly altered) from software. Do they already exist?
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13 votes
3 answers
10k views

How different are dc motor designs from dc generator designs?

Some dc motors can be used as generators as well by applying mechanical torque to the output shaft to induce a current. However, even if a dc motor can do this, I imagine they were not designed for ...
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13 votes
2 answers
8k views

How does a multimeter protect itself from high voltages?

I have used a cheap multimeter to measure voltages in simple DC circuits, but I have seen pictures of them plugged straight into the mains and used to measure various home-built generators. Why doesn'...
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13 votes
3 answers
313 views

How to correctly size the blades for a small educational wind turbine?

I want to design a small wind turbine that can be easily carried out of the classroom into the sports field in relatively low-wind conditions (5-15km/h) that can power a small ultra-bright 5V LED - ...
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13 votes
1 answer
868 views

What causes rechargeable batteries to age? What can be done to extend life of these batteries?

These days most of modern electronics use rechargeable batteries as a power source. Also, these days most modern rechargeable batteries are Lithium Ion or Lithium Polymer based. Like any other devices,...
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13 votes
1 answer
3k views

Why are bird flight diverters shaped like a spiral?

I was out walking and saw these strange looking spirals on some power lines. When I got home I did some research and discovered that they are to prevent birds form hitting the power lines, mainly ...
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12 votes
4 answers
809 views

Is interference between aircraft an issue for fly-by-wireless technology?

I was reading up on fly-by-wire development, and I saw a short section about fly-by-wireless technology. It seems like a great idea, with the potential to lower costs, weight and complexity. I can see ...
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12 votes
4 answers
4k views

Will more electricity be generated by using a lens to focus sunlight onto solar cells?

I have been wondering about this question for quite some time. Assuming an ideal case, the energy from photons hitting solar cells is converted into electric energy as described by the equation: $RI^...
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12 votes
3 answers
1k views

Thermoelectric Technology to Harvest Energy from Internal Combustions Engines

Background: In an automobile, only 1/3 of the potential energy in the fuel is converted into mechanical energy and significant portion of the energy is lost as heat. There have been previous ...
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12 votes
5 answers
3k views

Why is using steam to rotate a turbine more efficient?

For example i have an exhaust pipe with very hot air from burning biofuel, and i have a turbine at the end of the exhaust that rotates and generates electricity. Why is it more efficient to use the ...
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  • 417
12 votes
3 answers
8k views

Can a magnetic lock be negated or overcome by a stronger electromagnet?

Magnetic locks seem to be fairly common on the doors of modern buildings, but I question their reliability when compared to a traditional, mechanical lock. I realize that the strength that it would ...
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12 votes
1 answer
22k views

What are left justified and right justified ADC results?

The TI MSP430F20XX series has a 12-bit internal ADC output, which is right-justified. What is the difference between a left-justified output and a right-justified output? What are their pros and cons?...
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12 votes
1 answer
320 views

Why are typical UART baud rates not in multiples of 1000?

Why are typical baud rates not in multiples of 1000 instead of being in multiples of 300 i.e. 4800, 9600, 19200, 115200, etc...? Is there a mathematical or electrical reason behind this?
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12 votes
1 answer
487 views

What causes the sound coming from electrical vehicles?

All the electrical vehicles I've ever ride make that humming sound (either cars or trains). What exactly causes that sound? Is it drag force in the gears? Is it a fan? Or is it because of the coils (...
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  • 223
12 votes
2 answers
578 views

Does a Faraday cage effectively act as a notch filter?

In reading about Faraday cages, I have found that most "real world" designs incorporate multiple layers of mesh. For example, this article from the National High Magnetic Field Lab discusses several ...
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11 votes
3 answers
17k views

Defining the heap and stack size for an ARM Cortex-M4 microcontroller?

I have been working on and off on small embedded systems project on and off. Some of these projects used an ARM Cortex-M4 base processor. In the project folder there is a startup.s file. Inside that ...
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11 votes
1 answer
620 views

Avoid snapping an electric cable from too much rotation

I recently built the basic construction for a crane out of lightweight material. Basically the head of the crane contains an electric servo motor which spins the head of the crane by pushing itself ...
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11 votes
1 answer
1k views

How does a microbolometer (IR camera) work?

I am currently doing a project which has led me to my first encounter with IR cameras, and I am therefore quite curious as to how they operate. Specifically, I would like to know the following How is ...
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11 votes
1 answer
1k views

How fast should I sample with a logic analyzer?

If I have a 10 MHz digital signal, how fast do I need to sample with a logic analyzer to avoid any bit errors? Does the minimum sample rate increase if I want to attach a protocol decoder (e.g. SPI)? ...
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11 votes
1 answer
305 views

What is the significance of a diagonal input in a control diagram?

I have seen several block diagrams with diagonal inputs, drawn with an arrow through the block. and others like that (via Google image search) What is difference between this and a typical signal ...
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11 votes
1 answer
710 views

How do ultrasonic proximity sensors detect motorcycles differently from cars and trucks?

My car has ultrasonic proximity sensors to help me park. I've noticed that when motorcycles whiz past me the proximity alarm goes off. I originally thought that the motorcycles were just too close, ...
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11 votes
1 answer
3k views

How to calculate Power of motor when used as a generator?

How can you calculate how much power can be generated by a motor when used as a generator (like a motor used in a wind turbine)? Does the power depend on how fast the magnet is rotated? If so, is ...
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  • 323
11 votes
1 answer
2k views

Observability using the Discrete Extended Kalman Filter (EKF)

I have built (several) discrete Extended Kalman Filters (EKF). The system model I am building has 9 states, and 10 observations. I see that most of the states converge except one. All except 1-2 of ...
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10 votes
4 answers
4k views

Extending USB cable makes it not work

I have a camera that uses a USB cable to connect to my computer. I want to extend the cable from 3ft to about 6ft. Originally I just created my own cable, soldering 4 26AWG wires to a blank USB ...
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10 votes
4 answers
3k views

Are there different solar panels for recapturing energy from household lighting?

I have been investigating recapturing energy from house lighting using solar panels. Are there solar panels specifically designed to capture indoor lighting with a higher efficiency? If so, what are ...
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10 votes
3 answers
2k views

Harvesting thermoelectric energy from computer graphics cards

During CES2015 a well know Graphic Processor Unit (GPU) manufacturer introduced a new GPU. These GPUs need complex thermal management to keep the processor cool. Most GPU accelerator card ...
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10 votes
3 answers
813 views

Why don't we just build a giant wind turbine?

The power generated by a wind turbine is given by: $$\mathrm{Power} = \frac{1}{2}C\rho AV^3$$ Where: $\rho = \text{Air density}$ $C = \text{Coefficient of performance}$ $A = \text{Frontal area}$ $V ...
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10 votes
4 answers
192 views

How is the wattage of an incandescent light fixture determined?

I've seen light fixtures with varying wattage rating. From 30W to 100W even though the actual socket is the same. What is the limiting factor, why can't I put say a 75W bulb in a fixture rated at 50W?...
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10 votes
2 answers
3k views

Can a very bright light attract an incoming laser guided weapon?

I would like to know if a very bright light will attract an incoming laser guided weapon such as a laser guided missile. Say for example that a tank has a six-foot pole on the top of it and attached ...
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  • 249
10 votes
4 answers
12k views

Is it possible to "boost" a WiFi signal using an aluminum soda can?

I recently discovered that one of my roommates had attempted to boost the WiFi signal by cutting up a soda can and placing it near the router, like this: My roommate was probably following an ...
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  • 203
10 votes
4 answers
19k views

Does a transformer use power when output isn't under load?

I was reading about how AC to DC converters work with a step-down transformer and then a diode bridge to convert the lower, stepped down AC voltage into DC. What I don't understand is since the input ...
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  • 5,940
10 votes
2 answers
2k views

How are the thermodynamics of CPUs and other chips handled?

I hear that designing the thermal efficiency of such systems is very difficult. I'm not sure why, though, and I am interested. On the one hand, I bet the heat is somehow a function of the total power ...
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10 votes
1 answer
204 views

Saving RAM Memory when writing to 2K page size NAND flash

I am writing a driver for the Samsung K9WAG08U1D NAND flash chip. The specification of the memory chip mentions it has a page size of 2048 bytes (2kB). I am using a ...
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  • 481
10 votes
2 answers
263 views

What's this mystery symbol on a manufactured machine?

I hope this is the right place to ask this question; if not I'd really appreciate some tips as to where else I can go for answers. The symbol above (apologies for the blurry quality) is on a Chinese/...
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10 votes
3 answers
319 views

Bonding Semiconductors to PCB

I'm trying to bond semiconductor samples (Si and Ge) area ~1-2cm^2 to fiberglass printed circuit board (PCB) We use West system marine epoxy for other things. 105 resin 209 hardener (long cure time.) ...
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