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1500 questions
77
votes
2 answers
Crystals, Oscillators, and Resonators. What the difference?
I am trying to figure out the difference between crystals, oscillators, and resonators. I'm starting to grasp it but I still have some questions.
From my understanding, an oscillator is built from a crystal and two capacitors. What is a resonator…
Alexis K
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77
votes
3 answers
Push-pull/open drain; pull-up/pull-down
I am reading the datasheet of an ARM Cortex chip, specifically the GPIO chapter. Ultimately, I want to configure various GPIO pins to use them in "Alternate Function" mode for read/write access to SRAM.
Of all the GPIO registers available, I do not…
Randomblue
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76
votes
5 answers
What is the name of these little plastic things that protect wires from being cut into by the sharp edges of a drilled hole?
What is the name of these little plastic things that protect wires from being cut into by the sharp edges of a drilled hole?
Zhro
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76
votes
10 answers
How much voltage/current is "dangerous"?
Related:
Safe current/voltage limit for human contact?
From what I've heard:
110 V (or 220 V; household voltage pretty much) is dangerous (i.e. can kill you) I think there's consensus on this, no need to try :)
60 V (old telephone lines) is…
user541686
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76
votes
9 answers
Can a bird, previously at earth potential, get electrocuted by landing on a powerline at high-enough voltage due to the initial "equalization charge"?
At the voltage levels of typical overhead transmission lines in the US, a bird can land on one and be just fine (as long as it doesn't do something like spread its wings and touch a tree or something else at lower electric potential).
However, what…
etherice
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75
votes
6 answers
What happened to electrolytic capacitors in the 21st century?
We can sometimes see decades-old capacitors (such as ones made in the USSR) still working. They are bigger and heavier, but durable and not desiccating. Modern aluminium capacitors serve for about 11 years, if you are lucky, then become dry and…
Incnis Mrsi
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75
votes
10 answers
Why did LEDs take so long to appear as light bulbs?
LEDs are an old technology, why did the industries take so long to put them into light bulbs? Was there any technological gap missing?
PDuarte
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75
votes
4 answers
How is using a transformer for isolation safer than directly connecting to the power grid?
How is using a 1:1 transformer safer than using the mains straight off? Is it because you can limit the current coming from the transformer whereas straight from the mains its not current limited? I fail to see how its "safer" when playing with…
Dean
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75
votes
14 answers
My understanding of RC circuits is broken
I asked a relatively simple question. Unfortunately, the answers provoke far more questions! :-(
It seems that I don't actually understand RC circuits at all. In particular, why there's an R in there. It seems completely unnecessary. Surely the…
MathematicalOrchid
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74
votes
8 answers
Reasons not to use a 741 op-amp?
Simple enough question. Why not use a 741 op-amp in a target circuit or anyone's target circuit? What are the reasons not to use it? What might be the reasons to still choose this part?
Andy aka
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74
votes
3 answers
What is the ideal way to handle data pins D+ and D- on a USB power adapter to be compatible with fast charging on devices?
I have found that many USB wall chargers use a resistive voltage divider to set the D+ and D- pins to a specific voltage, usually between 2 and 3 volts. Other USB wall chargers short the D+ and D- pins together with no connection to anything else. …
ArraysStartAtSeven
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73
votes
4 answers
Securing electrical cables to holes in enclosures?
Suppose I would like to insert data-cables of varying diameters -- e.g., a cable of 5 mm diameter -- into the 6 mm diameter hole of a plastic enclosure. The wires within the cable are terminated via soldering to a PCB inside the enclosure.
What…
OrCa
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73
votes
11 answers
Why on earth are o-scopes earth referenced?
Thinking about it: You would never find a "Grounded" multimeter as robust and useful if a path to ground through the multimeter were introduced, modifying the circuit's behaviour and possibly damaging the multimeter with currents.
Why are so many…
Transient
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73
votes
3 answers
What does the Y capacitor in a SMPS do?
It seems that a well-designed SMPS has a capacitor connecting the ground planes of the primary and secondary sides of the transformer, such as the C13 capacitor here. What is the purpose of this capacitor?
I've let myself understand that it's for…
Dolda2000
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72
votes
6 answers
What is Copper Thieving and why use it?
On many boards I've seen, there are little copper dots used for the purpose of "Copper Thieving". They're small round copper dots connected to nothing and arranged in an array. Supposedly they're for balancing the copper on the boards to improve…
Gustavo Litovsky
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