Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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1500 questions
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3 answers

How is wristwatch with 10 years battery life possible?

Turns out Casio offers a handful of wristwatches with "10 year battery life". The claim is that thanks to "an advanced technology" the battery life in those watches is extended to ten years. Now if you look at different models you see that they are…
sharptooth
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Can an audio circuit be powered by a switched-mode power supply?

Most audio circuits are powered with large, heavy transformers and a small ripple after smoothing. SMPS are smaller and more efficient. EMI can be shielded by a metal enclosure and the output filtered for noise suppression. Especially where the…
Rob Kam
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What sensor to choose to track human presence indoors?

This is a hobby project about home automation. The idea is that of distributed system of cheap microcontrollers that take measurements, communicate, output data and control appliances. One important task that this system should perform is detect at…
Vorac
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6 answers

What are some ways to use relays more efficiently?

We often seem to use microcontrollers to control relays, and a 5 V microcontroller is often used with 12 V relays. A relay may need several times more power than the microcontroller. Not a problem if you can use an SSR, which you can drive at a few…
stevenvh
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4 answers

How efficient are LEDs?

Generally I see efficiency related to the lumens per watt, but what is the actual typical efficiency of LEDs in terms of electrical energy in to optical energy out? What sort of conversions apply?
Dirk Bruere
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4 answers

Why are LEDs on most embedded designs inverted?

I noticed, that on all my evaluation boards that I had up to this point in time. The LEDs were all connected in active low to the Microcontroller Port. I understand that from a safety view it's better to have active low RESET lines and such. But…
anyone
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3 answers

What resides in the different memory types of a microcontroller?

There are different memory segments to which various types of data are put into from C code after compilation. I.e: .text, .data, .bss, stack and heap. I just want to know where each of these segments would reside in a microcontroller memory. That…
stenvar
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Where is the Eagle component library for 0.1" breakaway headers?

I want to put some breakaway headers into my Eagle CAD file. By that, I mean these: Does Eagle come packaged with a library for these? If so, what is the part called, and which library is it in?
Eric
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12 answers

Is it really OK to supply more current than what the component is rated for?

In this heavily upvoted answer the answerer states that it is okay to supply a component with more current than what it's rated for. The analogy is that (paraphrasing here) "If Johnny wants to eat two apples, he'll only eat two regardless of whether…
Zac
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2 answers

Correct formula for LED current-limiting resistor?

I'm trying to work out what value resistor to use in a LED circuit. The equation I'd use to do this is: $$ R = \frac{V_{cc} - V_f}{I_f} $$ Seems logical, and makes complete sense. The answers to the question How do I calculate the resistor value for…
Jeremy Kerr
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4 answers

Negative voltage on AA battery

Last night I pulled the battery holder out of a toy RC car to test the voltage with my meter. The pack has 4 AA batteries. The combined voltage at the terminals of the pack was well under 1 volt, and then I tested each battery individually. These…
Carl Raymond
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7 answers

What happens if I omit the pullup resistors on I2C lines?

Just now I realized that the I2C data and clock lines (SDA and SCL) must have pullup resistors. Well, I've built a couple of clocks using the DS1307 RTC (see datasheet) according to the schematic below. Notice that I have omitted both pullup…
Ricardo
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7 answers

How is an XOR with more than 2 inputs supposed to work?

I've just started studying computer engineering, and I'm having some doubts regarding the behavior of the XOR gate. I've been projecting circuits with Logisim, whose XORs behave differently from what I've learnt. To me, it should behave as a parity…
gabrieljcs
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6 answers

What is "common-mode" noise?

Can someone explain what "common-mode" noise is, and how it can be problematic? I understand "noise" on a signal in general. If I have a "noisy" +5V rail on a circuit board, I'm not going to be getting a constant value of +5, it will be bouncing…
Adam Head
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2 answers

Difference between Brushless Motor and Stepper Motor

I think I understand the operating principles of a brushless motor and a stepper motor, but I'm a little confused about the difference. Is a brushless DC motor a very basic stepper motor? With proper controls, could a brushless DC motor be…
mrsoltys
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