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1500 questions
29
votes
9 answers
Is firmware code or data?
When someone says they "flashed" firmware to a device, I'm curious as to what this actually implies.
Is firmware just a native binary that is stored in memory and that can be interpreted by the device's CPU (like any other EXE on a computer)? Or is…
HeineyBehinds
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29
votes
10 answers
Why can't Wi-Fi run at 2.4 Gbit/s?
So Wi-Fi runs in the 2.4 GHz band, yeah (and the new ones 5 GHz)? Which means that every second, a Wi-Fi antenna outputs 2.4 billion square wave pulses, right?
So I was wondering, why can't it transmit data on every pulse, and be able to send data…
MC ΔT
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29
votes
4 answers
At what frequencies does PCB design get tricky?
I have designed many mixed-signal PCB's where the highest-frequency component is the microcontroller's crystal oscillator itself. I understand the standard best practices: short traces, ground planes, decoupling caps, guard rings, shielding traces,…
bitsmack
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29
votes
3 answers
Why did my fuse not blow?
I purchased a few fuses to get familiar with their workings, and I was surprised to see that the 100mA fast-blowing fuses I bought happily conducted up to 215mA (6V power supply, 10\$\Omega\$ resistor), where the filament just started glowing. I…
Duoran
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29
votes
10 answers
LM394 is obsolete. What is the new standard log amp circuit?
The traditional logarithmic amplifier circuit is described in National Appnote 311:
This circuit uses the difference of two transistor currents to generate the log of the input over a pretty wide range.
The well-matched transistor pair Q1a and Q1b…
markrages
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29
votes
6 answers
Is it better to route a pad to a trace, or a trace through a pad?
When routing a PCB, is it better to route a trace through a pad as in 1 below, or to route a pad to a trace as shown in 2 below?
Nate
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29
votes
4 answers
What is the usage of the negative voltages on a PC motherboard?
What is the usage of theses negative voltages? Are they there only for backward compatibility?
In nowadays PC power supplies, we have:
+12V
+5V
+3.3V
but also:
-12V
-5V
But the current rating of the negative rails are much smaller than the…
Blup1980
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29
votes
4 answers
Standard nomenclature for component types
What prefixes should be used on reference designators for components of various types? I think we can all agree that "R##" refers to a resistor, "C##" refers to a capacitor, and "L##" refers to an inductor. Beyond that, it appears to be a mishmash…
Kevin Vermeer
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28
votes
1 answer
Why does flash memory have a lifespan?
I've read that flash memories can "only" be reprogrammed 100000 to 1000000 times, until the memory storage "deteriorates"
Why exactly does this happen with flash and not other memory types, and what does "deteriorate" refer to, internally?
EDIT:…
triplebig
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28
votes
6 answers
Why are clocks used in computers?
As I know, a clock controls all of the logic operations, but it also limits the speed of a computer because the gates have to wait for the clock to change from low to high or high to low depending on the component. If no clock was incorporated, the…
skyler
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28
votes
5 answers
How to interpret the output of a 3-pin computer fan speed sensor?
I have a 3-pin 12 V computer fan and I want to interpret its speed sensor output. At the yellow wire I get something that looks like pulse-with modulation. How would I interpret the output without actually connecting the fan to a computer?
AndrejaKo
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28
votes
1 answer
Can I make KiCAD pcbnew NOT place all components at (0,0)
In EAGLE, when you create a board from an existing schematic or incrementally add components to a linked board/schematic project, it does not overlap components in the board file.
In KiCAD/Pcbnew I drew a schematic and created a board from it. Every…
HL-SDK
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28
votes
6 answers
How to choose right PWM frequency for LED?
I want to control LED's brightness with PWM (via BJT transistor). What frequency of PWM should I choose?
user54579
28
votes
3 answers
What happens at the end of a transmission line?
Let's say I wanted to make a widget containing a relay to switch between two antennas. There is a coax transmission line coming in from the transmitter, and two going out, each to a separate antenna. Inside is a relay which switches the center…
Phil Frost
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28
votes
3 answers
Ceramic vs. Film Capacitor: Which one is preferred in audio circuits?
I'm considering building an amplifier following instructions from a MAKE magazine article.
However, as I was reading the circuit schematic, I noticed that the author denotes that the capacitors C101, C104, and C105 are supposed to be "film…
apnorton
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