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1500 questions
44
votes
8 answers
Smallest AES implementation for microcontrollers?
Can anyone recommend a small, free implementation of AES-128 Rijndael for microcontrollers. Ideally, for the PIC18, though a general implementation in C would be useful.
Compiling the axTLS implementation for PIC18 and encrypting/decrypting a block…
Toby Jaffey
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44
votes
15 answers
What are low cost circuit and PCB design software?
Do you know of any freeware or low cost circuit / PCB design software?
I know a few which I have listed below but I was wondering if there were more of its kind. Please mention the good features and issues you've faced with the software.
Edward
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43
votes
3 answers
Why don't typical digital multimeters measure inductance?
Even with predominantly digital circuits, I am using inductors much more often than I used to, generally because of all the buck or boost converters (a recent board I was involved in has 12 different voltage rails -- six of them needed just by the…
tcrosley
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43
votes
3 answers
What's radiating on my PCB?
I recently did a proper EMC test on a PCB of mine. It failed the test, and seems to be radiating in the 300MHz - 1GHz region, with peaks every 50MHz, and little peaks on the 25MHz.
Looking at the near field, you can clearly see lots of 25MHz…
Rocketmagnet
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43
votes
7 answers
How does an antenna radiate (how do currents flow through the wire)
I don't understand how antennas radiate a signal.
I understand the basics of antennas (wavelength, electron E field, etc.), but I simply don't understand how a current can go through a wire that doesn't have negative pole.
Can you please explain…
depecheSoul
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43
votes
7 answers
Why is the unit for capacitance so large?
Most capacitors are in the µF, nF and pF range. I know there are some special ones that go that high, but at the time faraday was around, and the unit was named after him, they didn't have such a thing. Why is the unit so large if we rarely use caps…
skyler
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43
votes
11 answers
Is paralleling diodes a bad idea?
I'm trying to repair an 800W power supply (see my previous question on this.) One thing that gets me is that the design has two schottky diode packages (in TO-220) in parallel. I was always told this was A Bad Idea, but since they are thermally…
Thomas O
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43
votes
5 answers
Are decoupling capacitors needed with battery power?
Currently I run all my gadgets from batteries and don't use decoupling capacitors. Are they generally needed/useful when drawing energy from a battery?
Mr. Hedgehog
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43
votes
7 answers
What do I need for a basic RF circuit?
I'm looking for any resource that can help me build a very very basic RC circuit. I'm talking as simple as using RF to turn on/off an LED. The purpose of this circuit is for research and education. If anyone knows where I can get parts for simple RF…
Digital Brent
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43
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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43
votes
4 answers
Can somebody explain what IQ (quadrature) means in terms of SDR?
This is a bit of a basic question, but I am having trouble understanding why a signal needs to be broken up into I and Q components to be useful for software-defined radio (SDR).
I understand that the I and Q components are the same signal, just 90…
Malvineous
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43
votes
8 answers
Vias directly on SMD pads?
I was looking at an example board schematic provided by TI and I noticed something rather curious: vias were placed directly on SMD pads.
Is this a normal/acceptable practice to follow, or is it recommended/better to put a short trace and then have…
helloworld922
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43
votes
2 answers
Why wiggle nearby tracks on a PCB?
I've been reading an article (TheMagPi eMagazine) relating to the Raspberry Pi; "An ARM GNU/Linux box for $25."
In the article, page 17 at the bottom it shows an area on the Pi where a track zigzags next to a straight one with the explanation…
George Duckett
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43
votes
5 answers
Why do 7 segment LED displays break apart when I brush my teeth?
This question might sound silly, but it is very serious (although geeky, I must admit).
When I use my electric toothbrush in front of my alarm clock (one of those with a big red LED display), the numbers seem to break apart. Why?
With my current…
Max
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43
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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