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1500 questions
30
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6 answers
High PCB copper thickness: What are the pitfalls?
We need to carry high currents on a PCB (~30Amps sustained), so we are likely to order our PCBs with high copper thickness. So far we've only used 35 microns (1 oz) in our designs, so 'high thickness' for us means, 70 (2 oz) or 105 (3 oz).
We do not…
SomethingBetter
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15 answers
Intel HEX (.hex) viewer/readers
Lately I've been doing a lot of work with Intel HEX files. I want a program that can import an Intel HEX file and allow me to view the byte contents at each address.
There are a handful of programs I've seen that do this, but are there any that are…
Seidleroni
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30
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7 answers
What are the differences and similarities between FPGA, ASIC and general microcontrollers?
I have read this post and it does not answer my question in its entirety:
I think of a microcontroller as anything that has some memory, registers, and can process a set of instructions such as LOAD, STORE and ADD. It contains logic gates and such…
user58446
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10 answers
Why can a voltmeter still measure potential difference if it has a (theoretically) infinite resistance?
I am a physics teacher who did engineering and hated all things electrical! Hence when my students sometimes ask me how a voltmeter can measure the potential difference between two points if there is no current passing through the voltmeter. I can…
William Tabary-Peterssen
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30
votes
6 answers
What kilogram is doing in volt unit definition?
My question is inspired by this: Why do farads multiplied by ohms produce a result that has a unit of seconds?
I want to ask what kilogram is doing in this equation:
$$\mathrm{V = \frac{kg \cdot m^2}{A \cdot s^3}}$$
Kamil
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30
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2 answers
Connectorless USB on a PCB
I would like to make a board which can be plugged directly into the USB port of a computer, instead of using a separate male "USB-A" connector. I have seen this system used for very small USB memory keys, such as this one. How would I lay out a PCB…
drxzcl
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30
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5 answers
Is it safe to drive a MOSFET from an output pin of a microcontroller?
I have used commonly-available BJTs such as the 2N2222 and 2N3904 as switches by operating them in "saturation mode" from my MCU. I believe, however, that for these sorts of applications, a MOSFET is a more appropriate device. I have a few…
Mark
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30
votes
5 answers
What is the purpose of solder mask expansion?
I see recommendations of 2-4 mils for solder mask expansion. But why is it necessary?
ajs410
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30
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2 answers
What are the advantages of a shunt resistor vs. a hall effect sensor?
I'm constructing a boost converter, and I need to measure both the input current and the output current. Currents range anywhere from 25A to 200A, depending on the model. My controller is referenced to the negative rail of the converter. I've been…
Stephen Collings
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30
votes
6 answers
How to drive brushless motor with Arduino?
Is it possible to drive a brushless motor directly with Arduino? Or should I revert on controlling a brushless motor ESC with PWM pulses?
tuupola
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29
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7 answers
Where does U for voltage come from?
I believe in Europe the letter U is commonly used for voltage in (eg.) Ohm's law \$U = I × R \$. I think I understand where the letter V came from, commonly used in North America. But what's the story with U?
jippie
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29
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3 answers
Which has better efficiency: step-up or step-down switching voltage regulator?
I have a Lithium battery pack circuit that converts 4.2V (two 4.2V cells in parallel) to 5V.
Another option is to use a step-down converter from 8.4V (two 4.2V cells in series) to 5V.
Considering both cited circuits are well implemented, which…
dawid
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29
votes
5 answers
Charging lead-acid batteries?
Are there any special requirements for charging lead-acid batteries?
littlebirdceo
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29
votes
4 answers
Why is it bad to mix new and old batteries?
I've seen warnings that it's bad to mix new and old batteries -- why?
Is it a matter of a battery's age or a battery's voltage/current (remaining)?
Coldblackice
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5 answers
Why is it important for mains power supplies to be isolated?
In all the computer power supplies and other power supplies I've taken apart, I've noticed they are fully isolated from the mains. Galvanic isolation through transformers, and often optical isolation for feedback. There is usually a very visible gap…
Thomas O
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