Most Popular
1500 questions
46
votes
6 answers
How do I model an LED with SPICE?
What diode modifiers are used in practice to model LEDs with SPICE (Berkeley v.3f5)? These are available to me:
# Name Parameter Units Default Example Area
1 IS Saturation current A …
tyblu
- 8,167
- 6
- 40
- 70
46
votes
11 answers
Is there a dual of the transformer?
Capacitors and inductors are duals of each other.
A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?) Also, you can vary the ratio of voltages or currents by changing the…
endolith
- 28,494
- 23
- 117
- 181
46
votes
3 answers
What are these "dogbone" traces for on (1970s era) PCB?
I've been spending some time with some old PCBs from the 70s. I have seen this pattern on some, which are these short traces that appear as little whiskers in between each of the IC lead/leg through-holes. (This pic is obviously unpopulated.) They…
BZo
- 1,575
- 1
- 11
- 22
46
votes
5 answers
Why would an op-amp use BJTs over MOSFETs?
I've always been told that ideally, op-amps have infinite input impedance. So when I was looking at the LM741's transistor level schematic, I was confused when they used BJTs instead of MOSFETs.
Wouldn't using a BJT result in current flowing into…
Nate
- 1,658
- 3
- 15
- 19
46
votes
8 answers
Why are NAND gates used to make AND gates in computers?
Why is this a standard for AND gates
when it could be made with two FETs and a resistor instead?
theonlygusti
- 577
- 1
- 4
- 7
46
votes
6 answers
Why aren’t the main conductors in this underground power cable made from copper?
I’ve found a piece of electrical cable left by the electricity company that supplies the area. They did a repair recently underground.
I’m curious why the three big triangular conductors aren’t made from copper. It looks like aluminium to me, but…
i-CONICA
- 591
- 4
- 6
46
votes
3 answers
Why does an antenna trace have this shape?
I'm wondering why an antenna has a board trace that follows a certain "squiggly" shape. This doesn't have to apply to only antennas; I'm sure that there are other components that have changing paths for various reasons, but the antenna usually…
Ci3
- 805
- 1
- 9
- 13
46
votes
13 answers
How do I measure 10,000 A DC?
What is the standard way to measure a current of about 10,000 A? DC clamp meters seem to have only scales up to 2,000 A.
Edit
Some background of this question:
I am a high school physics teacher and I am trying to improve some classical experiments…
Julia
- 768
- 1
- 5
- 16
46
votes
2 answers
How is ASIC design different from FPGA HDL synthesis?
I've had some experience with FPGA/HDL tool suites such as Xilinx ISE, Lattice Diamond, etc. The general workflow is writing Verilog/VHDL, simulation, testing and then programming the FPGA.
I've heard a couple of people say ASIC design is very…
Robin Rodricks
- 866
- 4
- 10
- 14
46
votes
2 answers
What's special about 14.31818 MHz?
While desoldering useful components off of old computer hardware, I found quite a large number of 14.31818 MHz crystals.
This seemed odd to me. Why use such an irregular frequency with a very nontrivial conversion to human time units?
At first I…
FlashCactus
- 811
- 7
- 13
46
votes
7 answers
How do you document your hardware design decisions?
How do you document your hardware decisions in the design phase?
How do you avoid having to ask yourself the following questions while reviewing an hardware design that you made in the past:
Why did a choose this component?
Why/how did I choose…
m.Alin
- 10,638
- 19
- 62
- 89
46
votes
10 answers
Why is AVR used in Arduino?
Why is Arduino using AVR? I understand that they are the official processor but there isn't a reason the code couldn't be ported to an ARM or a Freescale architecture other than cost, right? As long as there is onboard memory, I figured there could…
Chris Gammell
- 1,541
- 1
- 12
- 25
46
votes
6 answers
Why is there a diode connected in parallel to a relay coil?
In most electrical circuits with a relay, a diode is connected in parallel to the coil of the relay. Why? Is it always a good practice?
Apostle
- 571
- 2
- 5
- 9
45
votes
5 answers
Is the neutral wire considered safe?
If the neutral wire carries current, why do many people believe that it's safe? I've heard "You can touch the neutral wire/bar in the breaker box and not get shocked. Only the hot can hurt you." If the circuit is complete and current is flowing,…
Stephen Melvin
- 762
- 2
- 6
- 12
45
votes
8 answers
Why are relays so frequently driven by optocouplers?
Since the advent of the many microcontroller development boards, like Arduino, there have been a number of relay modules sold to drive mains AC loads.
A lot of these seem to use an optocoupler, driver transistor and a relay to drive the load…
Cybergibbons
- 1,934
- 1
- 16
- 21