Voltage Spike
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Weird resistor with dots around it on the schematic
78 votes

It is a regular sense resistor with a kelvin connection or four terminal sensing. The dots are there to show a connection with the wires. A kelvin connection measures the current through the sense ...

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How do I identify SMD components? (or how do I identify any component)
Accepted answer
74 votes

Step 1) Identify the package, note how many pins, match up the pins first. Note that sometimes the package pins are underneath the part or extended away from the part. Also get the dimensions of the ...

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Why does Samsung include useless capacitors?
45 votes

At first I thought it might be purely mechanical, maybe a way to keep people from bumping the BGA part off the board, but the other two pictures suggest that it is not as the caps are surrounded by ...

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Why aren't CPUs cooled from below as well as above?
37 votes

They aren't cooled from below because they have pins on the bottom, and FR4 below that. Due to having a much lower thermal conductivity, $$ \begin{array}{rrl} \text{Copper:} & 385\phantom{.25} &...

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Why is an Ethernet cable not grounded?
34 votes

Why is Ethernet not grounded? There are two reasons: It would create a ground loop between devices The device would also be more susceptible to ESD which is prevalent in cables that are being moved ...

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Should I twist DC power and ground wires from a power supply?
Accepted answer
31 votes

Twisting wires reduces the magnetic loop area of the wires, this has two implications: Reduced susceptibility to noise from magnetic fields, with twisted wires an a smaller magnetic loop area, ...

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Why isn't there any 9.5 digit multimeter or higher?
31 votes

Four reasons: Because modern meters have an autoranging function. Because the dynamic range of the analog system would not support 91⁄2 digits, with a range of 1 V the noise floor would be in the ...

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Looking for circuit board material that can be dissolved
26 votes

Researchers from the National Physical Laboratory (NPL), in London, in cooperation with partners In2Teck Ltd and Gwent Electronic Materials Ltd, have developed a 3D printable circuit board that ...

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Does water actually damage or only temporarily disable electronics until drying out?
Accepted answer
21 votes

There are three ways water can damage components: Damage inside IC packages Corrosion Shorting or changing impedance. IC packages There are a lot of ICs that have a specified humidity tolerance, ...

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Hobby breadboard wiring guidelines to stay within legal RF/EMI limits?
21 votes

There isn't a reason to worry about exceeding limits with a breadboard, the FCC allows for building of single devices with no testing: What does this mean for a hobbyist? Very little, actually, ...

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Should I cool off in water the desoldered components?
Accepted answer
20 votes

Worse, if you look at the component packaging there is a thermal profile that is to be followed to ensure that the component does not experience thermal shock from expansion and contraction. Thermal ...

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How to secure cables to a PCB
19 votes

Cable ties are great. Just put two through holes in the PCB away from the connector. There are also a variety of flat tie holders that can also facilitate zip ties. These can be pushed in or fastened ...

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Why do some PCBs have the courtyard in the silkscreen layer?
18 votes

I do this all the time, the main reason being it allows a nicer visual appearance. The other nice thing about it is it enables a PCB designer to space components with minimum width between them. ...

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At what level of complexity should I consider UL listing my widget?
Accepted answer
18 votes

Its not about how much you sell or liability (a mark doesn't protect you from anything if you burn someones house down, but a safety mark will help prevent you from making mistakes) I would also like ...

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PCB Logic Board Reference Designator "E"
Accepted answer
17 votes

It's a pad for a flying probe test (which happens at assembly and you can see indentations from a probe or meter, if this is a production board then it's probably a flying probe test point). Flying ...

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Will my circuit charge the battery and power Arduino?
Accepted answer
17 votes

No, the maximum voltage of the LM2576 is 45V. There are also a few other problems with the schematic above: - You need to have an isolation transformer on AC mains for safety purposes - AC mains can ...

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What keeps the kickback voltage from reaching an infinite voltage?
Accepted answer
17 votes

A real inductor looks like this (shown below is an inductor with 4 coils) there is a small amount (usually in the pF-fF range) of capacitance between each coil. Each piece of wire also has some ...

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Fan-out of the Intel 8086
Accepted answer
17 votes

I actually wire wrapped an 8088 (which is similar) shown below and I did have to pay attention to fanout (my max fanout is 5, which you may be able to tell on some of the processor pins) Two words, ...

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Designing circuits with a longer lifetime
Accepted answer
17 votes

Before you start thinking about switching, make sure you have a good solid design. You need to start thinking about all the ways you could have problems in your design. A good way to do this is to ...

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Can PCB test points be a source of noise?
16 votes

Yes, test points can function like antennas, they can function like little antennas (and this is the reason why DRC in PCB tools sometimes check for small bits of copper that go nowhere and function ...

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Why does hot plugging blow stuff up, and how to prevent it?
16 votes

Hot swaping is bad for a few reasons: 1) If you connect the Vcc before ground current can flow into your circuit in anomalous ways. For example if Vcc is connected and a digital or analog pin before ...

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What is the definition of absolute maximum ratings?
Accepted answer
16 votes

So, short story is the definition of absolute maximum rating does vary from manufacturer to manufacturer. Most every manufacture (of those sampled) will give a variation of this warning: Stresses ...

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How does Ethernet magnetics work?
Accepted answer
16 votes

There are a few bad things that the system was designed to mitigate, one is ESD, noise and ground loops. The first transformer (up down one) is an isolation transformer, it passes the high frequency ...

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Solder paste storage
Accepted answer
15 votes

But what exactly will go wrong when it is stored at a higher temperature or past its shelf life? Solder paste is composed of metal microballs and flux. The metal doesn't change over time much; the ...

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Are MOSFET drains ESD sensitive?
Accepted answer
15 votes

Yes, mosfets drains are sensitive to ESD. If you look at the Vds spec in the datasheet, it cannot be exceeded (for the IRF530, it's 100V), even for short amounts of time. ESD over-voltage conditions ...

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Why do some PCBs have exposed plated perimeters?
Accepted answer
15 votes

They are called via fences, they are placed on the outside of the board to "fence in RF", they do this by creating a barrier smaller than the wavelength that needs to be shielded. At very high ...

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Beginner's second PCB circuit design: AC to DC
15 votes

Per IPC spec you need creepage and clearance, even if your not using this in a product (and getting it tested at an ETL). Source: http://www.ni.com/white-paper/2871/en/ That means if you have AC ...

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Why can't you just average ADC samples to get more resolution from an ADC?
15 votes

The short answer is noise, and its not necessarily the noise that matters, but the type of noise. The other problem is nonlinear effects like INL that throw off the average value First on to Noise: ...

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How do power grid systems supply power to new loads coming online?
Accepted answer
14 votes

Where that additional 5MW of power came from instantly until the power system frequency go down and active power governors speed up the generators (obviously there is a time delay)? The voltage on ...

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Effect of length on a thermocouple's accuracy
14 votes

Wire cable resistance is insignificant when compared to the input impedance of the amplifier which is so high that the wire doesn't affect the measurement. For example, the LT1052 (which would be ...

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