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1500 questions
33
votes
5 answers
Can I turn Radio waves into light?
Wikipedia says that the frequency of light is 300 THz.
I've made a radio waves transmitter that transmits about 100 MHz.
If I increase the frequency of the transmitter to 300 THz, will the antenna produce spark or light ?
Can I do this circuit…
Michael George
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33
votes
6 answers
Reducing voltage with resistors
I have been looking around for an easy way to convert 12V to 5V. I have seen some people saying that a simple resistor is all that is needed.
$$ Volts = Ohms \cdot Amps $$
$$ Amps = \frac{Volts}{Ohms} $$
$$Ohms = \frac{Volts}{Amps}$$
So applying a…
Konner Rasmussen
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33
votes
5 answers
What reasons are there to avoid vertical through-hole resistors?
I'm working on a layout for a PCB and I need to include a handful of pull-up resistors. The board I'm working on will be a proof of concept, and it is likely I will only need one (and order two). That being said, I'd like to keep the board area…
Justin Trzeciak
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32
votes
7 answers
What is the advantage of a Z transform derived PID implemenation?
I've seen many PID articles, such as this, use a Z transform of the generic PID equation to derive some crazy difference equation which can then be implemented in software (or in this case an FPGA). My question is, what is the advantage to such an…
bt2
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32
votes
7 answers
Possible to cut heat shrink tubing lengthwise and reattach?
I need to get some heat shrink tubing around something that is too big on the ends for it to slide over. Is it possible to cut the heat shrink along it's length and somehow reattach it before applying heat to get it to shrink?
If you have any…
stbtra
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32
votes
2 answers
Should I use lead free solder?
I have been a hobbyist solderer for about 6 years now, and my skills are very proficient. I have always used lead solder because my experience with lead free solder is awful. But I'm going to college in a few months and I just upgraded to a very…
Sponge Bob
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32
votes
5 answers
What is the significance of -3 dB?
My oscilloscope has 100 MHz -3dB bandwidth. -3dB is 0.707 units (\$\sqrt{2} / 2\$). What does this mean, why 70.7% attenuation? Is there any particular reason for this attenuation level?
Thomas O
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32
votes
7 answers
Arduino Uno R3: Directly supply regulated 5V to 5V pin?
I'd like to use an Arduino Uno R3 battery powered a datalogger. I want do supply it directly with a Step-Up regulated 5V rechargable battery powersource at power pin 5V.
I don't want to suppy it with 5V at the PowerJack or Vin because it's not…
try-catch-finally
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32
votes
4 answers
Why aren't resistors being used in this flip-flop used in static MOS RAM?
In the book, Digital Computer Electronics, there is a diagram on page 140 (figure 9-4 a) of a flip-flop used in static MOS RAM to store a bit. The book says that Q3 and Q4 act like resistors, which leads me to wonder, why aren't normal resistors…
Nitin Singhal
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32
votes
1 answer
Darlingtons, MOSFETS, and bipolar junctions
I realize there are dozens upon dozens of kinds of transistors, each used for specific purposes. Sometimes there is great overlap; multiple kinds may work in a given circuit, but at times only a specific transistor is ideal.
Without reading all of…
JYelton
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32
votes
6 answers
Why does 60 Hz mean 60 refreshes and not 120?
A light bulb using alternating current at 60Hz turns on and off 120 times per second but in a monitor 60Hz means 60 refreshes per second.
Why is that? Shouldn't 60Hz mean 120 refreshes?
isar
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32
votes
8 answers
Why don't we use lenses for RF?
Radio waves are a class of electromagnetic waves.
Light also is a class of electromagnetic waves.
By shaping a material in which the speed of light changes, we can bend the propagation direction of light, we call this a lens, and we call the speed…
valerio_new
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32
votes
5 answers
Optocoupler with phototransistor base lead
I'm thinking about using 4N25 optocoupler - it has a separate lead for base of phototransistor. How do I use it? I suppose I can't leave it floating?
miceuz
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32
votes
1 answer
Why are the E-series numbers different from the powers of 10?
The E-series numbers are the common values used in resistors. For example, the E6 values are:
1.0
1.5
2.2
3.3
4.7
6.8
As you can see, each is about \$10^\frac16\$ apart. But I wonder why they aren't the powers of \$10^\frac16\$ rounded to 2…
7h3yskr8
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32
votes
5 answers
LTspice: Vary a resistor's value over time
I want to simulate the load regulation of a power-supply. I'm sure I remember being able to vary the value of a resistor over the course of a simulation in LTspice, but I can't remember how. Anyone?
volting
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