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57
votes
5answers
5k views

Can I cut an IC?

As far as I understand, the die of a DIP package is located at the center and the rest is just the lead frame. Given that I have unused pins, can I cut the top part of this microcontroller (ATmega16/...
57
votes
2answers
28k views

In a USB cable, is it OK to swap the D+ and D- wires?

I heard that D+ and D- are differential signals, does it matter if I swap them when connecting a USB device to the computer?
56
votes
7answers
16k views

Does a dangling wire really electrocute me if I'm standing in water?

We've all seen this scenario in movies; somebody has to cross a room half filled with water and there is a dangling electric wire that shoots sparks everywhere. The poor person has to cross the room ...
56
votes
5answers
93k views

How to choose value of resistor in voltage divider?

I understand that the output voltage is determined by the ratio between the two resistor values, and that if the both resistors are same then output voltage will be exactly same for all; but what's ...
56
votes
10answers
55k views

Why is main's neutral tied to earth?

My dad is an Electrician and I myself am an Electronics Design Engineer, and to this day he still hasn't been able to give me a good reason for this. Consider the two following pictures/situations - ...
56
votes
3answers
10k views

Fan speed switch: why OFF :: HIGH :: MED :: LOW?

Many AC fans, including inexpensive floor models, have a rotary speed control which rotates from OFF to HIGH to MED to LOW. Since the switch does not rotate 360°, you have to rotate it backwards to ...
56
votes
8answers
15k views

Why weights on cables between utility poles?

Yesterday I saw what look like weights hanging from a cable between utility poles. This was in northeast Arizona on Route 60 between Show Low and Springerville. Here is a picture of a whole span: ...
56
votes
4answers
149k views

How to choose a flyback diode for a relay?

A diode is put in parallel with a relay coil (with opposite polarity) to prevent damage to other components when the relay is turned off. Here's an example schematic I found online: I'm planning on ...
56
votes
2answers
36k views

"Remove After Washing" on Piezo Buzzer

Maybe this is a stupid question, but here goes: I just got a piezo buzzer and on the top there is a sticker that says "Remove After Washing". My question is why would I ever want to wash an ...
56
votes
3answers
33k views

Which products should have FCC certification and about how much does that cost?

I'm aware that nobody actually does this at the hobbyist level, that successful commercial products have been launched without certification, and it's probably something I can't afford if I have to ...
56
votes
6answers
11k views

Does my Arduino-based device need FCC certification?

I've built a small consumer device that contains an Arduino Nano. It's coupled to a custom daughter board that allows it to pulse a 12V electromagnet at about 1 hertz as well as inteface to some ...
56
votes
8answers
106k views

Can an Android tablet serve as USB Host and be charged simultaneously through a single port?

A number of Android tablets are powered through the Micro B USB port but also provide USB Host support through the same port (e.g. Motorola Xoom 2, Acer A510/700). I need to be able to use USB Host ...
55
votes
11answers
37k views

Why would clipping a wire cause a bomb to explode?

There are a lot of movies and video games that depict defusing bombs, most of which boils down to picking the right color wire. Something like this: Now, that's a part I don't understand. simulate ...
55
votes
10answers
20k views

Why is there no `nand` instruction in modern CPUs?

Why did x86 designers (or other CPU architectures as well) decide not to include it? It is a logic gate that can be used to build other logic gates, thus it is fast as a single instruction. Rather ...
55
votes
10answers
11k views

Amplification before tubes and transistors were invented

Telephones are older than vacuum tubes and of course transistors. How was signal amplification done? I mean the technology, not the details. EDIT Some additional informations that I should ...
55
votes
5answers
47k views

Triac versus Relay

What are the scenarios where Triacs can not replace a relay or vice-versa?
55
votes
4answers
63k views

Why do we use 32.768 kHz crystals in most circuits?

Why do we use 32.768 kHz crystals in most circuits, for example in RTC circuits? What will happen if I use a 35 or 25 kHz crystal? I assume because the IC internal Xin, Xout pin circuitry should be ...
55
votes
3answers
14k views

What's this importance of datasheets?

As someone starting with electronics I keep hearing, "Check the datasheet!" Why are datasheets so important and what information can I expect to find in them? It seems like a large amount of ...
55
votes
5answers
12k views

Are LEDs better than we think?

Conventional wisdom about LEDs says their maximum reverse voltage \$V_{R(max)}\$ is quite limited, usually in the 5V-8V range. So, for experimentation purposes, I wanted to bring an LED into ...
55
votes
5answers
49k views

Programming microcontrollers: JTAG, SPI, USB oh my!?

I've noticed, with regards to microcontrollers, there are several way to program them. I am sorta familiar with USB as my Arduino's can be programmed via USB. What is a JTAG or SPI interface? ...
55
votes
5answers
87k views

Stripboard/veroboard/matrix board design software

I'm prototyping a simple layout for a small project on matrix board, but figured there must be a better way than drawing it all out on paper. Are there any aimed at matrix board? I've found the ...
54
votes
10answers
44k views

Why is an Ethernet cable not grounded?

There is no dedicated GND in the classical Ethernet 8P8C ("RJ45") pinout.[1] Why does the Ethernet spec not include a ground, unlike many other cable types used for interconnecting devices that may ...
54
votes
13answers
12k views

What kind of components in a computer power supply can explode loudly?

Today I heard a loud bang that tripped the circuit breaker in my server room. It must have been really loud because I could hear it 2 rooms away through 2 heavy doors and it was like a firecracker ...
54
votes
5answers
44k views

How can PCB trace have 50 ohm impedance regardless of length and signal frequency?

Hmm, this seems to be just another question on line impedances. I understand that when we say "transmission line" effects we talk about things like cross talk, reflections and ringing (I guess that ...
54
votes
6answers
128k views

Do I really need resistors when controlling LEDs with Arduino?

I'm just trying out Arduino Uno for the first time with 2 blinking LEDs on a breadboard. All the tutorials on the Internet seem to use a resistor. I do know the function of resistors, but does it ...
54
votes
5answers
65k views

When to use pull-down vs. pull-up resistors

After learning and experimenting with microcontrollers, I've understood the concept of pull-up- and pull-down resistors. I now understand when and how to use them, and how they work. I've mainly used ...
54
votes
3answers
9k views

How do lasers measure short distances (<1cm) when electronics are too slow for time-of-flight to work?

I was wondering how LIDAR sensors are able to measure distances less than 2mm. I don't see how they can possibly do that. The speed of light is 300,000,000 m/s, so the round-trip time should be ...
53
votes
9answers
48k views

How safe is 48V DC?

In many Power over Ethernet (POE) setups the transmission voltage is 48V or slightly more. While higher voltage has obvious efficiency advantages, how safe it is? Is there any risk of electrocution ...
53
votes
6answers
16k views

Why do transformers use so many turns?

Transformers have hundreds of turns on both the secondary and primary winding, and as a result use very thin copper wires for each. But, why do they not just use fewer turns on each winding and get ...
53
votes
3answers
6k views

What is the purpose of tiny "bumps" on LED legs? [duplicate]

A lot (if not most) LEDs have some kind of small thickenings on their legs. Sometimes they are almost as wide as the leg itself and barely visible, sometimes they are twice as wide and instantly ...
53
votes
3answers
35k views

What does 3V3 or 1V8 mean?

While reading a datasheet for an IC I came across the pin voltages being presented as 3V3 or 1V8. What does this representation stand for?
53
votes
4answers
77k views

JTAG vs SWD debugging

After skimming through this article, I am wondering what are the benefits of SWD debugging over JTAG debugging? I understand SWD uses less wires/pins, takes up less space etc. But how does it play ...
53
votes
7answers
84k views

What exactly is a current source?

What I understood from the definition of current sources is that it is a source which supplies a constant current across a load no matter how the other parameters (like resistances for example) in the ...
53
votes
8answers
6k views

Personal electronics tool kit

What are the items you have in your personal electronics tool kit?
53
votes
2answers
24k views

What is the latency of an LED?

LEDs are known to have a very low, unnoticeable power-cycling latency, but how fast are they when measured? (nanoseconds?) In other words, how long does it take for an LED which is entirely off to ...
53
votes
2answers
14k views

Why are USB devices slower than 480 MBit/s

Motivation With a signaling rate of 480 MBit/s USB 2.0 devices should be able to transmit data with up to 60 MB/s. However today's devices seem to be limited to 30-42 MB/s while reading [Wiki:USB]. ...
52
votes
2answers
64k views

Calculating the pulldown resistance for a given MOSFET's gate

I searched and read many similar questions, but did not find a specific answer for how to calculate the correct value for a pulldown resistor for a MOSFET's floating gate. It seems like everyone ...
52
votes
5answers
37k views

Is a CAN enabled microcontroller sufficient to drive a CAN bus?

There are a number of CAN modules built into microcontrollers these days. The PIC18F2480 is an example of that. Is that microcontroller (with built-in CAN) capable of driving a CAN bus on its own or ...
52
votes
7answers
62k views

What is the usage of Zero Ohm & MiliOhm Resistor?

I am new to PCB design and I noticed that some schematics use 0Ω or 100mΩ resistors. What is their purpose and why do we need to use them in our PCB design? Normally if we wish to probe how much ...
52
votes
5answers
7k views

Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

I built a prototype keyboard/sound synthesizer using a chain of 13 astable multivibrator circuits whose outputs are connected to an audio amplifier chip (LM386) and speaker, all powered off a 9V DC ...
52
votes
3answers
15k views

How to go from a development board to a production board?

Ok, I am a software guy and new to electronics. My product needs a small computer and currently I have developed everything on development boards like raspberry pi and such. As the development board ...
52
votes
5answers
35k views

Why does more transistors = more processing power?

According to Wikipedia, processing power is strongly linked with Moore's law: http://en.wikipedia.org/wiki/Moore's_law The number of transistors that can be placed inexpensively on an ...
52
votes
6answers
101k views

What gauge of single strand wire works well with breadboards?

I bought some single strand wires hoping to prototype on the breadboards. Unfortunately it was too small to properly fit into the breadboard holes. So my question is which gauge fits well on those ...
52
votes
5answers
10k views

I don't care how a transistor works, how do I get one to work?

Every reference I can find on transistors immediately launches into theory-heavy alphabet soup. The above seems also to be assumed knowledge for reading a datasheet. I don't care; I just want to get ...
52
votes
6answers
153k views

Maximum I2C Bus Length?

What is the maximum length of cable that could be used to connect two I2C devices (I2C master-> I2C slave)? Yes, I know that I2C is really designed for intra-board communication. I have been tasked ...
51
votes
16answers
60k views

Why use PLC instead of microcontroller?

Why does everyone use PLCs in industrial environments, instead of a microcontroller based solution? For a longer task, the PLC program is as complicated as a microcontroller program. A ...
51
votes
8answers
96k views

Can a 12V battery give you a shock or not?

I am reading a book called "Make: Electronics" and, on page 9, it says: "Anyone who has dropped an adjustable wrench across the bare terminals of a car battery will tell you that short circuits can ...
51
votes
17answers
37k views

Complete alternatives to the Arduino IDE? [closed]

I'm not that big of a fan of the official Arduino IDE (in terms of visuals), so I've started looking for nicer alternatives. However, most of the projects I've found are in alpha/beta and are ...
51
votes
5answers
11k views

Why do you need 2 resistors when hooking up a transistor as a switch

What is the point of R2 in the following diagram: I get that R1 controls the current to the Base, but what does R2 do?
51
votes
2answers
48k views

What's the third wire on a piezo buzzer?

Most piezos I've seen have just two connections, but this type has three. What's the third wire for?

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