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1500 questions
176
votes
6 answers
What is the reason that the value "47" is so popular in electrical engineering?
We often see component values of 4.7K Ohm, 470uF, or 0.47uH. For example, digikey has millions of 4.7uF ceramic capacitors, and not a single 4.8uF or 4.6uF and only 1 listed for 4.5uF (specialty product).
What's so special about the value 4.7 that…
MandoMando
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173
votes
12 answers
How does the current know how much to flow, before having seen the resistor?
With the following circuits as examples :
and
How will the current I know how much to flow?
Would any other wave travel first in the circuit and then come back
and say so much current should flow?
Prabhanjan Naib
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157
votes
4 answers
How can I efficiently drive an LED?
I understand that I can not connect an LED directly to a battery because it will draw too much current. Thus, there must be something else in the circuit to limit the current.
What options are there? Are some methods more efficient than others?
Phil Frost
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157
votes
6 answers
Why exactly can't a single resistor be used for many parallel LEDs?
Why can't you use a single resistor for a number of LEDs in parallel instead of one each?
Dataflashsabot
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136
votes
7 answers
Designing a Santa alarm (honestly)
You read the title and that's what I am trying to do.
Synopsis: I have a young son who is determined to catch Santa (to what ends I don't know). He even dreamed up using some kind of pressure plate and connecting it to a light that will turn on when…
Christian Bongiorno
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133
votes
6 answers
Should chassis ground be attached to digital ground?
I'm working on a PCB that has shielded RJ45 (ethernet), RS232, and USB connectors, and is powered by a 12V AC/DC brick power adapter (I do the 5V and 3.3V step down on board). The entire design is enclosed in a metal chassis.
The shields of the…
cdwilson
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131
votes
5 answers
Why does Samsung include useless capacitors?
I do component-level repair of tablet mainboards, and I have seen this puzzling situation on two different models of Samsung tablet mainboards so far (SM-T210, SM-T818A). There are ceramic chip capacitors on the PCB that are clearly connected to…
Crash Gordon
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126
votes
7 answers
What measures should I take to protect the USB ports of my PC during development of a USB device?
I'm going to start developing a USB 1.1 device using a PIC microcontroller. I'm going to keep one of the USB ports of my PC connected to a bread board during this process. I don't want to destroy my PC's USB port by a short circuit or connecting…
hkBattousai
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125
votes
10 answers
Are solder fumes bad for me?
I do a fair bit of soldering (lead-free). Is breathing in solder/flux/paste fumes actually going to harm me?
Are cheap fume extractors worth buying?
Toby Jaffey
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123
votes
7 answers
Why does micro USB 2.0 have 5 pins, when the A-type only has 4?
What is the extra, 5th, pin on micro usb 2.0 adapters for?
Here is an image with the different connectors. Most of them have 5 pins, but the A-type host only has four.
(source: wikimedia.org)
Sponge Bob
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121
votes
9 answers
Tradeoffs when considering SPI or I2C?
What tradeoffs should I consider when deciding to use an SPI or I2C interface?
This accelerometer/gyro breakout board is available in two models, one for each interface. Would either one be easier to integrate into an Arduino…
Mark Harrison
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121
votes
5 answers
Difference between UART and RS-232?
Most of the time RS-232 and UART come together in serial communication theories. Are they both the same? From my readings I concluded UART is a hardware form of the RS-232 protocol. Am I correct?
tollin jose
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120
votes
7 answers
What’s the proper soldering iron temperature for standard .031" 60/40 solder?
I recently purchased a Weller WES51 soldering iron as my first temperature controlled iron and I'm looking for recommendations on the best default temperature to use when soldering.
I'm using mainly .031 inch 60/40 solder on through-hole components.
Redwood
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119
votes
7 answers
What limits CPU speed?
I've recently talked with a friend about LaTeX compilation. LaTeX can use only one core to compile. So for the speed of LaTeX compiliation, the clock speed of the CPU is most important (see Tips for choosing hardware for best LaTeX compile…
Martin Thoma
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118
votes
4 answers
Why Are Ethernet/RJ45 Sockets Magnetically Coupled?
As the title says really, why do ethernet sockets need to be mag-coupled? I have a basic understanding of electronics, but mostly, I can't figure out the right search terms to google this properly.
slugonamission
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