Most Popular
1500 questions
38
votes
3 answers
What are those weird wires in the audio cables?
Trying to repair a headset cable, I discovered that it doesn't look at all like the “ordinary” cables I used to repair. I was expecting to see, inside the cable jacket, four wires, each one in a wire insulation. Instead, there is:
A wire with a…
Arseni Mourzenko
- 834
- 1
- 12
- 20
38
votes
3 answers
Help me understand the relationship between positive, negative, neutral and ground in AC and DC
This question stems from notations on schematics and seemingly conflicting information I'm seeing. I suspect that I'm seeing different vernacular for the same concepts--but I'm in a place where no one's ever told me that an "elevator" is a "lift".…
dwwilson66
- 3,432
- 11
- 33
- 43
38
votes
10 answers
What are some smallest, cheapest microcontrollers with USB built in?
The cheaper, smaller, and fewer external components needed the better.
AVR would be preferred, but anything with free SDKs is good.
tlrobinson
- 549
- 1
- 4
- 5
38
votes
8 answers
Add a passive hardware token using a 3.5mm jack
I have a box that I made for my niece, which allows her to exchange voice messages with me. It is powered by a Raspberry Pi and features two buttons, a LED, a microphone and a speaker.
Now, for Christmas I want my niece to be able to exchange these…
Besi
- 737
- 1
- 7
- 18
38
votes
4 answers
Why can the regenerative brakes of the Oslo Metro only share energy with other trains if they are "nearby"?
I read on Wikipedia that the Oslo Metro has regenerative braking, but no batteries to store the energy. Therefore, the energy can only be utilized if there is another train "nearby" to utilize the energy.
How far is "nearby"?
Due to the bottleneck…
Fiksdal
- 942
- 2
- 9
- 18
38
votes
2 answers
How did this capacitor survive having a nail driven through it?
How did this metal film 1 uF 630 VDC polystyrene capacitor survive having a nail driven through it while under a voltage of 122 VAC? It is part of UL testing for potential X or Y grade capacitors, which it MUST pass to be put on UL's approval list.…
user105652
38
votes
8 answers
How to prototype?
How is prototyping done in a professional EE environment? Do you do your prototypes on breadboards, on copper clad boards, Manhattan style, or do you just draw schematics, order PCBs made and assembled and work with them, hacking here and there if…
miceuz
- 5,561
- 3
- 40
- 51
38
votes
3 answers
What does it mean to "assert a pin"?
From the XBee/XBeePro product manual page 24 (link to pdf):
Sleep Modes enable the RF module to enter states of low-power consumption when not in use. In order to enter Sleep Mode, one of the following conditions must be met (in addition to the…
Lucy Brennan
- 593
- 3
- 8
- 11
38
votes
5 answers
Why does a commercial PCB need this much rework?
I found a PCB that has had some rework done. When I saw it, I thought that someone had actually repaired it after purchase:-
It's got additional wiring (white & brown) and under the hot glue are two ceramic capacitors. The capacitors have been…
Paul Uszak
- 7,517
- 5
- 40
- 76
38
votes
2 answers
BJT in Reverse Active Mode of Operation
What will happen if for a BJT transistor, it's emitter terminal is treated as collector and collector as emitter in a common emitter amplifier circuit?
Ravi Upadhyay
- 555
- 2
- 5
- 8
38
votes
5 answers
How can a one million megohm resistor be useful?
I used to do periodic maintenance on a detector system for low-power-level particles. Its circuitry included a one million megohm resistor. It was in a sealed solid brick made maybe of Bakelite, about 4"x2"x0.5". I mean, isn't there less resistance…
RichF
- 1,311
- 1
- 12
- 14
38
votes
4 answers
Identifying Source of Periodic Artifact at Op-Amp Output
My MAX44251 dual op-amp has a very small unwanted 131KHz periodic artifact at the output, seemingly regardless of how it's configured.
My assumption was EMI, but I can't see this 131KHz signal on any other part of the circuit. I've also tested this…
Keegan Jay
- 1,280
- 1
- 11
- 29
38
votes
2 answers
How does current get into a diode?
I think I understand more or less how an ordinary semiconductor diode works: Crystal doped differently in different regions, carrier depletion where they meet, bla bla bla.
However, actual diodes that one builds circuits with do not end with bits of…
hmakholm left over Monica
- 698
- 5
- 13
38
votes
2 answers
How does a chip antenna work?
There are many guides to using chip antennas, with and without baluns, PCB layout considerations, etc., but I've been unable to find any information on how chip antennas work at a fundamental level, and how they're manufactured.
Can anyone provide…
Daniel Schuler
- 483
- 1
- 4
- 5
38
votes
3 answers
What is this suspicious stain under a VFD's glass?
I wanted to give VFDs a try so I ordered a couple of 8x14 segments display modules.
They arrived today, but I'm concerned because each has a big black stain in the corner. If it were on an LCD I'd suspect they're broken, but since I don't know this…
LeFauve
- 503
- 5
- 6