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1500 questions
22
votes
6 answers
Does Impedance Matching Imply any Practical RF Transmitter Must Waste >=50% of Energy?
According to the maximum power transfer theorem, when a fixed source impedance is given, the load impedance must be chosen to match to the source impedance to achieve maximum power transfer.
On the other hand, if the source impedance is not out of…
比尔盖子
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22
votes
10 answers
STM Microcontroller burns every time
I have some experience working with stm32 but I only ever used them on dev boards.
I recently tried to solder stm32 and stm8 on a simple break-out board and program them with my st-linkv2 clone.
On first power up, the mcu makes some little noises…
NXP
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22
votes
7 answers
Why is USB Type-A to USB Type-A never used?
I was wondering why almost all USB cables that exist are USB-A to (Micro-USB | USB-C | USB-B | etc.)
Why was USB-A to USB-A not a popular thing? Is there a technical reason this cannot work?
NessDan
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22
votes
4 answers
Different PCB color (is it a different material?)
I have acquired this PCB.
The right side of the PCB handles high voltage AC power (250 V maximum,) while the left side handles low DC voltages (24 V maximum.)
They are separated, not only by board cuts, but also with this yellowish line in the…
Malek
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22
votes
4 answers
Crystals and load capacitance
If a crystal has a rated load capacitance of 6 pF, is the right thing to do to put a 6 pF capacitor to GND on either leg of the crystal? I'm using it as the clock source (TOSC) for an XMEGA and it's got a max ESR of 50 kOhm (which is within…
vicatcu
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22
votes
7 answers
Necessity of an external watchdog timer
What is the need for an external watchdog timer for a microcontroller?
Most of the microcontrollers are designed with an internal watchdog timer. However, in some of the circuits they are using an external watchdog timer (such as PIC16F1824).
Photon001
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22
votes
9 answers
Make a momentary switch control a toggle
What are the simplest, cheapest, smallest ways to make a momentary switch produce a 2-state toggling output (latching momentary switch)?
In other words, the output is continuously low, and when you momentarily press the button/tact switch, the…
endolith
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22
votes
3 answers
What is the name of this springy type oscilloscope probe accessory?
Exactly what it says on the tin.
How is this pictured accessory called? The obvious place to look for a name would be the probe manual, but it looks like they decided to add the accessory to the package after making the manual, since it's not on…
AndrejaKo
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22
votes
2 answers
Solution for adapting to USB current draw limits?
Summary: I'm setting up a USB-powered Li-ion charging circuit and would of course like to draw the maximum charge current possible situationally -- but also want to ensure I don't violate the USB specification on current draw. While I have been able…
boardbite
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22
votes
10 answers
How exactly does AM/FM carry both pitch and loudness of voice?
Almost every tutorial on AM/FM modulation shows the modulating signal as something like a simple tone or continuous sine wave. Now that's easy, and for AM you just superimpose the modulating signal over the carrier wave as an envelope, and voila,…
aAaa aAaa
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22
votes
2 answers
Why is there no rolling shutter when using a mechanical shutter?
So I know it might not be the best place to ask this question, but maybe some of you are familiar with the mechanics of digital mirrorless cameras and the technology of CMOS sensors.
I don't quite understand why electronic image sensors, that create…
Thomas D.
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22
votes
2 answers
What is a brownout condition?
I'm reading the datasheet of this DAC. Page 27 states:
In many industrial process control applications, it is vital that the
output voltage be controlled during power-up and during brownout
conditions.
What are "brownout conditions"? Why is…
Randomblue
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22
votes
2 answers
Some advice on charging circuit used in simple UPS
I have looked around for some way of having a 5 volt power supply that acts like a UPS.
Basically want to use a micro usb connector for +5 have a battery and li-ion or other charging circuit that will maintain uninterrupted power on the output.
I…
Piotr Kula
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22
votes
5 answers
Resistors - metal film or carbon film and what values?
I am buying a bunch of resistors as a start to my electronics hobby. These are the values I have chosen:
100, 470, 1k, 4k7, 10k, 33k, 47k, 100k, 470k, 1M
Most of my projects will involve microcontrollers, such as the Arduino and other AVR ones. I…
capcom
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22
votes
3 answers
How are multi-layer PCBs made?
I know how normal PCBs are etched, but every time I grab a magnifying glass and examine the edge of a multi-layer board I'm astounded by the precision that must be required during production. On top of that, some of them have buried vias and other…
Polynomial
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