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1500 questions
27
votes
1 answer
What is the polarity of a car cigarette lighter adapter?
There is a center pin, and two outside tabs. Which are positive and negative?
Mark Harrison
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27
votes
2 answers
Three legged NOT gate? What is this symbol?
I've come across the above schematic in a datasheet for a 4x2:1 bus switch. What exactly does that triangular symbol on S mean? It looks a lot like a NOT gate, but the third leg is confusing me.
Bo Thompson
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27
votes
11 answers
Why not make one big CPU core?
I don't understand why CPU manufacturers make multi-core chips. Scaling of multiple cores is horrible, this is highly application specific, and I am sure you can point out certain program or code that runs great on many cores, but most of the time…
wav scientist
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27
votes
5 answers
What's the highest theoretical energy density for a chemical battery?
This is more a physics/chemistry/nanotech question, but what's the theoretical best energy density you could get out of a chemical battery (or fuel cell), if you could arrange atoms in any manner you wanted? I'm thinking of the nanotech batteries…
endolith
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27
votes
3 answers
Why do many electronics operate on 5 and 3.3 volts?
Many modern appliances use a 5V power connection, but internally they work with 3.3V. Wouldn't it be easier to have 5V everywhere?
Examples are many USB devices or routers (they use 5V for power but 3.3V for serial communication.)
Moe
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27
votes
3 answers
UART & USART - What's the difference
In the office I hear these terms thrown around as if they are the same. My understanding is that USARTs can deliver the clock signal along with the data.
Are there any other differences? What are the advantages and disadvantages of each?
waffleman
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27
votes
8 answers
Is CAT5 cable good enough for RS-485 vs "true" RS-485 cable
I have a serial comms project coming up. A number of boards with RS-485 interfaces need to communicate. Date rate is 57600bps and cable length will be less than a few hundred feet.
Will shielded CAT5 cable work well enough in this situation or…
SeanLabs
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27
votes
10 answers
Can a high voltage line kill a person without touching it?
It's common (for me) to hear that a HV power line can kill a person without touching it "if they entered its field." I'm not convinced by this reason and I think it quite naive and that it doesn't clarify anything.
Warning: Video shows people…
iMohaned
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27
votes
7 answers
Why is this power adapter transformerless?
I saw a battery charger that converts 220V AC to 6V DC without a transformer.
Now I am wondering why many (if not all) power adapters are using a transformer, is it about efficiency or about drifting over time?
Update:
This circuit is inside of…
Jim
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27
votes
6 answers
How do I describe this circuit?
simulate this circuit – Schematic created using CircuitLab
Yes, this circuit diagram is correct. No, I did not design it.
How do I describe this circuit in words? I thought about "a switch and light bulb in parallel, instead of series" but the…
dpdt
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27
votes
13 answers
Is voltage the speed of electrons?
Current is the amount of electrons passing through a wire. Can we say that voltage is the speed of those electrons?
money-printer
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27
votes
5 answers
Why are Edison screws allowed to be used?
Why are the Edison screws allowed to be used? They seem unsafe. Why are they designed that way?
They require a complete grounding system to ground devices for the rare situation where the hot wires somehow touches the metal case of the device
While…
ronenfe
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27
votes
3 answers
Why are deep cycle batteries rated in amp hours instead of watts hours?
Why are deep cycle batteries rated in amp-hours instead of watt-hours? For example if I see a 85Ah battery, I multiply 85Ah x 12V to get 1020 watts. As household electricity use is measured in watt hours (hence a kill-a-watt) this information seems…
Mauvis Ledford
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27
votes
3 answers
What does it mean when multimeter accuracy is marked as: ±0,03%+10Digit?
I have a digital multimeter and its accuracy for VDC is marked like this:
±0,03%+10Digit
This multimeter has maximum display of 80000. So in the 80 V range it can show for example 79.999V.
0.03% of 80V is 0.024V - that is clear for me. But what…
ria
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27
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6 answers
Why are relatively simpler devices such as microcontrollers so much slower than CPUs?
Given the same number of pipeline stages and the same manufacturing node (say, 65 nm) and the same voltage, simple devices should run faster than more complicated ones. Also, merging multiple pipeline stages into one should not slow down by a factor…
Michael
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