Most Popular
1500 questions
25
votes
6 answers
Why do we use capacitors in parallel with DC motors?
Below is the circuit diagram of an L293D motor driver IC driving 2 12V DC motors.
What I don't understand is the use of the capacitors marked 104 in parallel with the motors.
Bhavik Khatri
- 369
- 1
- 3
- 5
25
votes
2 answers
What's the meaning of Electrical Inches?
I was reading a PCB design notes and guidelines from Xilinx for their 7 series FPGAs and came across this sentence:
The capacitors should be placed as close as possible to the FPGA. Any
placement within two electrical inches of the device’s point…
AdoobII
- 419
- 4
- 13
25
votes
4 answers
Pass USB 3.0 connection through D-SUB connector
I need to pass a USB cable through a vacuum chamber wall, for which we have only D-SUB passthrough flanges available. So I cut a USB cable in half and soldered a D-SUB connector to each half. For USB 2.0 connections, this works without any issues,…
Lukas Lang
- 433
- 4
- 9
25
votes
3 answers
Strange LED behavior: Why is there a voltage over the LED with only one wire connected to it?
I am encountering a strange problem when I measure the voltage across an LED. Please see below picture:
As you can see, I only connected 1 wire ("-") of adapter and used a multimeter to measure the voltage drop across the LED and I found there is…
Tom Lin
- 332
- 3
- 6
25
votes
13 answers
Examples of fluid (including air) being used to transmit digital data?
We usually use electrons to communicate data across wires, and sometimes we use light also. Does anyone know of real world example systems that use fluids (including air) to do this, and the advantages vs using wires? When I search for air pressure…
Ryan Griggs
- 2,686
- 2
- 33
- 55
25
votes
2 answers
Why do radiation hardened IC packages often have long leads?
What purpose do long leads serve?
Dojo
- 949
- 11
- 19
25
votes
4 answers
Why the arc when bonding-on during high voltage repairs?
When working on high voltage power-lines via helicopter the technician will "bond-on" with a steel wand called a hot-stick. During this process an arc is conducted from the line to the wand. Now, since the helicopter is floating both literally and…
Salbando Jones
- 331
- 3
- 8
25
votes
7 answers
What's the point in a preamp?
I'm talking in the context of guitar amps, but I assume that this question is relevant for any type of audio amplifier.
Very often in amplifier schematics I see two stages of amplification -- first, the signal is amplified a smaller amount by a…
Jacob Garby
- 714
- 1
- 9
- 19
25
votes
3 answers
How to improve torque and RPM of a DC motor?
I have an FA-130 motor (DC) with permanent magnet, my power source is a 2 AA batteries (rechargeable) so a total of 2.4v.
Assume that all cases will start from the same specification, theoretically, what would happen if I do the following?
Case 1:…
kazinix
- 353
- 1
- 4
- 5
25
votes
14 answers
How is it that two electric currents can travel in opposite directions on the same wire, at the same time, without interfering with each other?
An Introduction to Information Theory: Symbols, Signals and Noise, by John R. Pierce, says the following:
While linearity is a truly astonishing property of nature, it is by no means a rare one. All circuits made up of the resistors, capacitors,…
The Pointer
- 1,261
- 1
- 14
- 26
25
votes
5 answers
Why are SRAM based FPGA used more than NVM based FPGA?
SRAM based FPGAs need to load the bitstream again after power off. Meanwhile the Non-Volatile based one don't need that.
I wonder, why are more experiments and security research done on the SRAM FPGA than the the NVM based one, it seems that the…
Lavender
- 527
- 1
- 5
- 11
25
votes
3 answers
Is the LED drop voltage difference between colors linked to the different wavelength energy?
To me appears that LEDs that emitt light with less energy (e.g. IR and red) have less voltage forward drop than the ones with more energy associated to their wavelength (such as blue or UV).
That would be fascinating.
Is this a true correlation or…
valerio_new
- 1,642
- 2
- 15
- 27
25
votes
1 answer
How to do pulling up or down correctly when interfacing a microSD card?
I have seen people pulling up only the CS pin, so that when the microcontroller's pins are floating in the power-up, the microSD card is not corrupted.
Also, I have seen many people pulling up and down DI,DO and SCLK lines.
Some of the circuits that…
abdullah kahraman
- 5,970
- 8
- 60
- 104
25
votes
5 answers
What are 12.000393 MHz crystals used for?
I found them on www.digikey.com, and they're apparently made by different manufacturers, so there must be some use for them. What are they used for?
edit
and why? The 2400 baud modem doesn't offer an explanation: a 12 Mhz crystal is better for that…
Federico Russo
- 9,688
- 17
- 69
- 119
25
votes
4 answers
Strong adhesive to attach part to PCB
I am looking for recommendations for a strong adhesive that would be easy to apply by hand in production quantities. This is for fastening an ABS plastic riser in between two PCBs.
Epoxy would work, but we would need to make sure the set time was…
BrianV
- 550
- 1
- 6
- 13