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9 votes
Accepted

Can a capacitor be used to close path between center-tap and shield instead of Bob-Smith (capacitor+resistor)?

Why not both? You can series a resistor and capacitor just fine. The capacitor should be some 10s of nF, I suppose, so that its peak (AC) voltage during ESD is small (the 1nF still handles most of it)...
Tim Williams's user avatar
  • 39.8k
8 votes

KiCAD symbols for JST connectors

There are hundreds of "generic" connector symbols in KiCAD. Choose one that matches the pin numbers on the footprint and use it in your schematic. Then allocate the footprint to the symbol ...
Andy aka's user avatar
  • 465k
8 votes
Accepted

Why does IPC 2221 require so much more spacing at elevation?

It comes from the Paschen's Law. The following graph is a Paschen curve taken from this research. The graph may look a bit awkward to make a conclusion as "required clearance increases with ...
Rohat Kılıç's user avatar
7 votes

Attaching foam to the bottom of a PCB

Unless there are heat producing or high power devices that are counting on airflow for heat rejection, a closed-cell flame-retardant, adhesive-backed foam would work. Knowing students however, ...
vir's user avatar
  • 20.4k
6 votes
Accepted

PCB layout for 16 MHz crystal oscillator

No it is not acceptable, the crystal needs to be close to the pins to minimize EMI. In this case I believe the pins are named XTAL1 and XTAL2. From each pin you should have as short a trace as ...
Lundin's user avatar
  • 21.2k
6 votes
Accepted

Schematic component

No and Yes. You have circled both a fuse F1 and a ferrite bead FB16. The wavy component is the fuse, rated 5A. The ring with wire through is the ferrite bead. Ferrite beads are typically rate d at ...
Justme's user avatar
  • 159k
5 votes

PCB layout for 16 MHz crystal oscillator

Is the layout acceptable? You should use a full ground plane for this type of design. It cost pennies to make your PCB 4 layer from 2 layer and will save you hours of messing around trying to locate ...
Andy aka's user avatar
  • 465k
5 votes
Accepted

Contains floating input pins

Schematic ERC is a, somewhat archaic mechanism nowadays, but its purpose is to ensure connectivity in a logic design. Back in the day, sheets of logic, making enormous boards full of chips, was the ...
Tim Williams's user avatar
  • 39.8k
5 votes

Attaching foam to the bottom of a PCB

PCB pillars are a purpose designed tool for the job: While the foam that comes on them is self adhesive, if you don't remove the backing paper they're quite usable as a movable soft contact with the ...
user1908704's user avatar
5 votes

High frequency digital (2GHz+) and PCB manufacturability with FR4?

Amongst the problems with FR4 as you push it beyond 2 GHz are loss, tolerances, and dispersion. Many high speed physical interfaces are tolerant of a reasonable amount of loss, and can be tuned to the ...
Neil_UK's user avatar
  • 169k
4 votes

Attaching foam to the bottom of a PCB

You might look at using something like hobby wood, thin wood sheets typically made of basswood. You could have mounting holes in each corner of your circuit boards and maybe one or two in the middle, ...
GodJihyo's user avatar
  • 25.1k
4 votes
Accepted

Will such a scheme work correctly with ATmega328PB?

Firstly, I suggest working on your diagram. A hard-to-read diagram will almost inevitably have mistakes. Specifically about the circuit: Where are the decoupling caps? How does ...
jonathanjo's user avatar
4 votes

Unexpected Loss In Signal Integrity

I also didn't add a ground plane because I didn't know how to do it at that time. That's the primary source of the problem. Even though the display is connected directly to the board, the signal has ...
Kuba hasn't forgotten Monica's user avatar
4 votes

Attaching foam to the bottom of a PCB

Unless the desk is perfectly flat with nothing on it, and you carve out bits of the foam where the through-hole component legs are, a layer of foam across the whole board is unlikely to sit flat on a ...
Tom Carpenter's user avatar
4 votes

How to show pad designators at any zoom in Altium

I just found the solution! I know this might not be bothering you any more, but I was so frustrated by Altium's defaults and the confusing responses you got here that I want to save anyone else who ...
Spencer's user avatar
  • 41
4 votes

Why does IPC 2221 require so much more spacing at elevation?

It's more of a one (or two, in this case) size fits all strategy. If you don't want to deal with calculating the exact factor for the altitude at which you'll be operating, then the values given will ...
vir's user avatar
  • 20.4k
4 votes

Custom PCB to make a high-precision, low-current voltage source "fix" drift in a lower-precision, high-current current source

No need for high-side sense, in fact it's better low-side. Other changes are suggested as well: Note the Yokogawa isn't doing much here, and can be discarded. U3 is setting reference. If you need ...
Tim Williams's user avatar
  • 39.8k
4 votes

Deciphering workings of a printed circuit board for a night-light

A capacitive dropper is used to create a low DC voltage. This design is non-isolated, so it should only be used when the circuit can't be touched. https://en.wikipedia.org/wiki/...
Mattman944's user avatar
  • 16.5k
3 votes

Schematic component

The wave part is the symbol for a fuse. It is rated for 5 A and is in a 1210 surface-mount package. To the right of it is a ferrite bead. DNP stands for Do Not Populate. It might be something left ...
AnalogKid's user avatar
  • 21.4k
3 votes

Deciphering workings of a printed circuit board for a night-light

The usual way is to trace it out; one of the best ways is in a drawing package with layers, for example the open source package Inkscape. You put the top and bottom images lined up (here bottom is ...
jonathanjo's user avatar
3 votes

Is a shunt jumper for a power plane jumper a good idea?

It's fine if you are comfortable with adding 50 to 100milliOhms of contact resistance and a small amount of inductance to the rails. I'd leave the caps in.
Voltage Spike's user avatar
  • 85k
3 votes

Is a shunt jumper for a power plane jumper a good idea?

Beats me -- depends what the circuit is, what's on the other side of it. But regardless of that, I can express what possible concerns I would expect, and what alternatives I would consider: Ampacity. ...
Tim Williams's user avatar
  • 39.8k
3 votes

High Insertion Loss on 4 Layer 5.8 GHz Board

Issues I see: I don't see bypass capacitors near the power supply pin of U2. You have traces on (I think) L2 pretty close to your high speed traces, breaking the reference plane for these traces. ...
The Photon's user avatar
  • 131k
2 votes

GND plane between tracks or tracks closer enough to remove the GND tracks

This video from Rick Hartley about PCB grounding and grounding in electronics in general is great if you want to learn more in details. This one from Phil’s lab talks more about PCBs in general and ...
vorobey's user avatar
  • 103
2 votes

Help me to identify an SMD component marked 'NM' in an SOT-89 package

I think @Tony is correct, the photos match lcsc's listing for the 2SCR533P5T100 and 2SCR533PT100. The latter is NRND and the difference between the two appears to be grade related- the electrical and ...
Spehro Pefhany's user avatar
2 votes

Is there any issue if I put vias too densely?

The following is a list of all the potential issues I can think of: Most obvious is that the vias act as an obstacle to routing traces on all layers (unless they're blind vias, but using blind vias ...
Hearth's user avatar
  • 35.3k
2 votes

Is there any issue if I put vias too densely?

Too much congested vias can create many problems. Dense vias under components, such as MOSFETs, can cause issues during soldering. If thermal vias are placed directly under pads, they can wick solder ...
liaifat85's user avatar
  • 125
2 votes

GND plane between tracks or tracks closer enough to remove the GND tracks

Broadly in general: A. Depending on via density, this has the most shielding between traces. For your described scenario: B. While A might be strictly better in EMC terms, the amount by which it's ...
Tim Williams's user avatar
  • 39.8k
2 votes
Accepted

DC-DC SEPIC convertor design

This only makes sense when looking at the copper pour, not at the schematic. The point of this is to keep the power ground isolated from the regular ground, so that the pour areas are only connected ...
Lundin's user avatar
  • 21.2k
2 votes

Attaching foam to the bottom of a PCB

My answer would be very much the one of GodJihyo, except it you get your PCB manufactured industrially, you might give a try at getting a 2nd "PCB", except with just holes for standoffs/...
user1532080's user avatar

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