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1500 questions
46
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11 answers
What would happen if I connect two different DC voltage sources in parallel?
I have a computer power supply that I'm hacking together as a bench supply. For this particular model to power on, I need a minimum load across both +5V and +12V.
"Easy," I thought, "I'll just connect both +5 and +12 to my power resistor!" And it…
rascher
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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
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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
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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
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45
votes
8 answers
How to resolve I2C address clashes?
I want to connect multiple I2C slave devices to a micro controller all on the same set of pins but the I2C devices all share the same address. The addresses are fixed in the hardware.
Is there any way to connect multiple devices with the same…
Simon P Stevens
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45
votes
9 answers
Why use capacitors?
Why do you need to store the voltage for some time in a capacitor? I've always assumed circuits to work when you power it on and stop when you power it off.
Why can't the whole circuit be drawn capacitor free? If it's meant for storage why not just…
user1424
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45
votes
3 answers
What are the advantages of this gold finger shape?
Some PCBs, like the PCI card specification have gold fingers which start very narrow near the bottom edge, and gain their usual width much higher, where the actual contact is expected to be made.
What is the advantage of having the narrow part?
Why…
akwky
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45
votes
5 answers
For a lower voltage drop one could use Schottky diodes, but what are the disadvantages of Schottky's?
In other words, why don't we always use Schottky diodes if they are so much better? What diode properties do Schottky diodes have that makes them unfit for certain applications?
jippie
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45
votes
5 answers
How can I use a 12 V input on a digital Arduino pin?
I am creating a controller for a 12 V system using an Arduino Uno microcrontroller. For the outputs I am using a relay shield to switch the 12 V components. I have a 12 V toggle switch that turns on some 12 V components in the system and I want to…
D.W.
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45
votes
3 answers
What are the advantages of having two ground pours?
I've seen many 2-layer PCBs that have a ground pour on both the top and bottom layers, I was wondering why do that ? and wouldn't it be better to use the top layer for power and signals and the bottom layer for ground to simplify the routing and…
mux
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45
votes
8 answers
Why is 50 Ω often chosen as the input impedance of antennas, whereas the free space impedance is 377 Ω?
In order to efficiently deliver power to a different part of a circuit without reflection, the impedances of all circuit elements need to be matched. Free space can be regarded as a further element, since a transmitting antenna eventually should…
DK2AX
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45
votes
3 answers
Minimum operating temperature - Outer Space?
I've been looking at some microcontrollers and I've seen they've got some "weird" minimum operating temperatures, like -25 degrees or -10 degrees etc. But I can't really understand why there is a minimum, a maximum I do understand because everything…
Harry Svensson
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45
votes
5 answers
How can cache be that fast?
Here is a screenshot of a cache benchmark:
In the benchmark the L1 cache read speed is about 186 GB/s, with the latency being about 3-4 clock cycles. How is such a speed even achieved?
Consider the memory here: the theoretical maximum speed is
665…
Knight
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45
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
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45
votes
8 answers
Which configuration is better for pulling down an NPN transistor's base?
I was discussing on pull down resistors with a colleague of mine. Here are the two configurations for transistor as a switch.
The input signal can either come from a microcontroller or an another digital output to drive a load, or from an analogue…
abdullah kahraman
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