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1500 questions
39
votes
2 answers
Should I discard my inventory of old electrolytic capacitors?
I have been doing hobby electronics for more than 10 years, and some of my electrolytic capacitors are easily that age. They seem to work just fine and do not show corrosion or other visible defects, but they are usually used in prototyping rather…
JYelton
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39
votes
5 answers
Why does a faster clock require more power?
If you overclock a microcontroller, it gets hot.
If you overclock a microcontroller, it needs more voltage.
In some abstract way it makes sense: it is doing more computation, so it needs more energy (and being less than perfect, some of that energy…
Jack Schmidt
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39
votes
8 answers
Saving Arduino sensor data to a text file
How can I save data retrieved from a sensor to a text file on the computer?
desNotes
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39
votes
3 answers
What is the difference between I2C and TWI?
What is the difference between the I2C and TWI interfaces? Wikipedia says that TWI is variant of I2C. Some other sources says that only name is different.
user54579
39
votes
3 answers
Computer power supplies usually have higher efficiency on 230V than on 115V. Why?
As seen here in the example, this particular power supply (and most others too) has higher efficiency when running on 230V. Given that computer power supplies are usually required to output a combination of 12V, 5V, and 3.3V DC, why is it that…
cyqsimon
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39
votes
6 answers
Why does Intel's Haswell chip allow floating point multiplication to be twice as fast as addition?
I was reading this very interesting question on Stack Overflow:
Is integer multiplication really done at the same speed as addition on a modern CPU?
One of the comments said:
"It's worth nothing that on Haswell, the FP multiply throughput is
double…
Nike Dattani
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39
votes
7 answers
VHDL: Converting from an INTEGER type to a STD_LOGIC_VECTOR
I built a mod-16 counter, and the output result is a INTEGER (all the examples I saw used INTEGER).
I built a hex-to-7-segment-display decoder, and its input is a STD_LOGIC_VECTOR (wrote it that way because it was easy to map out the truth…
J. Polfer
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39
votes
9 answers
Why V rms instead of V average?
I'm looking at an equation for average power in a signal
$$
p_{avg} = \frac{1}{R} v_{rms}^2
$$
and wondering why it isn't
$$
p_{avg} = \frac{1}{R} |v|_{avg}^2
$$
Rob N
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39
votes
6 answers
Switch between 5V power supplies?
I'm designing a board that can be powered either by USB or an ATX power supply. They can both be plugged in at the same time, independently. I'd like the ATX to provide 5V if its plugged in, but fall back to the USB if possible. The chips in the…
Zach Hoeken
39
votes
5 answers
Why is the time constant 63.2% and not 50% or 70%?
I am studying about RC and RL circuits. Why is the time constant equal to 63.2% of the output voltage? Why is it defined as 63% and not any other value?
Does a circuit start working at 63% of output voltage? Why not at 50%?
Bala Subramanian
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39
votes
13 answers
Software to create timing diagrams
In my professional life, I sometimes need to create timing diagrams for protocols: UART, SPI, etc. However, I can't find any good programs available. What programs can be recommended for this and what is the experience using them?
Seidleroni
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39
votes
1 answer
If I am measuring 2.3 V on a 1.5 V AA battery from Duracell, is my multimeter broken?
I recently measured a brand new Duracell AA battery which is labeled as 1.5 V. The reading was 2.3 V. Is this ever normal for a fully charged battery, or is my multimeter broken?
merlin2011
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39
votes
7 answers
How were schematics drawn before CAD?
I was looking at the schematic of an old HP power supply I bought. It can be found here, around page 60-61.
This schematic was drawn long before CAD was a tool used by engineers. Things were still drawn by hand. I was wondering how drawing large…
Joren Vaes
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39
votes
8 answers
Why does Ohm's law not work for vacuum cleaners?
I have been learning about Ohm's law and testing the resistance across the plug of my household appliances and calculating the current.
For example, my kettle was 22 ohms (10.45 amperes) and is protected by a 13 A fuse.
This makes sense, and I'm…
Dominic Edwards
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39
votes
5 answers
Why should you use two resistors in parallel on an LED?
So I was looking over the Arduino R3 schematics and noticed this little design choice:
What is the reason for doing something like this? I mean it's hard to know what the designers were thinking, but maybe it was done this way to save space. Do you…
Jake Robinson
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