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347 votes
8 answers

What is the difference between \$V_{CC}\$, \$V_{DD}\$, \$V_{EE}\$, \$V_{SS}\$

I've seen lots of schematics use \$V_{CC}\$ and \$V_{DD}\$ interchangeably. I know \$V_{CC}\$ and \$V_{DD}\$ are for positive voltage, and \$V_{SS}\$ and \$V_{EE}\$ are for ground, but what is the ...
  • 5,814
336 votes
6 answers

Why is there so much fear surrounding LiPo batteries?

I've been trying to design a charging system for a small robot powered by a 2S 20C lithium polymer (LiPo) battery. Were I to trust everything I read online, I would believe that the LiPo will kill me ...
  • 4,339
316 votes
8 answers

Rules and guidelines for drawing good schematics

There are a lot of poorly drawn schematics here. A few times people have actually asked for critiques of their schematics. This question is intended as a single repository on schematic drawing rules ...
311 votes
6 answers

Choosing power supply, how to get the voltage and current ratings?

Power supplies are available in a wide range of voltage and current ratings. If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to ...
291 votes
38 answers

Basic Electronics Book [closed]

I need basic electronics books (diodes,transistors,current.. etc) as I am just starting out with electronics and want to have something to read over the holiday. Any suggestions of good beginners' ...
272 votes
3 answers

What is it that strips vocals from audio when a 1/8" audio jack is partially unplugged?

Every once in a while, my eighth-inch audio jack will slip loose and I'll seemingly lose only the voice part of a track -- leaving somewhat of a "karaoke" version. What I would guess about how audio ...
  • 2,461
247 votes
9 answers

Decoupling caps, PCB layout

I guess I've been somewhat ignorant when it comes to the finer details of pcb layout. Lately I've read a couple of books that try their best to lead me on the straight and narrow. Here is a couple of ...
  • 4,583
238 votes
37 answers

Good tools for drawing schematics

I was going to add a bit of information to my post on a previous day using schematics and some instructions. What programs are being employed for this purpose? I mostly want to see what others are ...
219 votes
7 answers

Why was Mini USB deprecated in favor of Micro USB?

Mini USB connectors were standardized as part of USB 2.0 in 2000. In 2007, the USB Implemeters Forum standardized Micro USB connectors, deprecating Mini USB connectors four months later. Why? What ...
  • 2,091
214 votes
17 answers

What is a decoupling capacitor and how do I know if I need one?

What is a decoupling capacitor (or smoothing capacitor as referred to in the link below)? How do I know if I need one and if so, what size and where it needs to go? This question mentions many ...
  • 4,275
204 votes
13 answers

What's the difference between a microcontroller and a microprocessor?

What's the difference between a microcontroller and a microprocessor?
  • 28k
195 votes
8 answers

Why does USB have 4 lines instead of 3?

USB specifies 4 pins: 1. VBUS +5V 2. D- Data- 3. D+ Data+ 4. GND Ground Why is this not 3? Could the Data and Power not share a common ...
194 votes
4 answers

USART, UART, RS232, USB, SPI, I2C, TTL, etc. what are all of these and how do they relate to each other?

As a novice electronics hobbyist, I have heard these terms and more being thrown around everywhere. At its root, I understand that they are all based on communication between devices, computers, ...
  • 5,782
183 votes
10 answers

How much does it cost to have a custom ASIC made?

I have browsed several ASIC manufacturer's webs, but I haven't found an actual number. I assume there would be a fixed cost associated with creating masks and such and then there will be a cost per ...
  • 2,944
181 votes
16 answers

Is C++ suitable for embedded systems?

A common question, here and elsewhere. Is C++ suitable for embedded systems? Microcontrollers? RTOSes? Toasters? Embedded PCs? Is OOP useful on microcontrollers? Does C++ remove the programmer too ...
174 votes
12 answers

How does the current know how much to flow, before having seen the resistor?

With the following circuits as examples : and How will the current I know how much to flow? Would any other wave travel first in the circuit and then come back ...
172 votes
6 answers

What is the reason that the value "47" is so popular in electrical engineering?

We often see component values of 4.7K Ohm, 470uF, or 0.47uH. For example, digikey has millions of 4.7uF ceramic capacitors, and not a single 4.8uF or 4.6uF and only 1 listed for 4.5uF (specialty ...
  • 3,162
154 votes
6 answers

Why exactly can't a single resistor be used for many parallel LEDs?

Why can't you use a single resistor for a number of LEDs in parallel instead of one each?
152 votes
4 answers

How can I efficiently drive an LED?

I understand that I can not connect an LED directly to a battery because it will draw too much current. Thus, there must be something else in the circuit to limit the current. What options are there? ...
  • 55.7k
136 votes
7 answers

Designing a Santa alarm (honestly)

You read the title and that's what I am trying to do. Synopsis: I have a young son who is determined to catch Santa (to what ends I don't know). He even dreamed up using some kind of pressure plate ...
128 votes
5 answers

Why does Samsung include useless capacitors? [closed]

I do component-level repair of tablet mainboards, and I have seen this puzzling situation on two different models of Samsung tablet mainboards so far (SM-T210, SM-T818A). There are ceramic chip ...
  • 1,236
125 votes
7 answers

What measures should I take to protect the USB ports of my PC during development of a USB device?

I'm going to start developing a USB 1.1 device using a PIC microcontroller. I'm going to keep one of the USB ports of my PC connected to a bread board during this process. I don't want to destroy my ...
  • 13.6k
125 votes
6 answers

Should chassis ground be attached to digital ground?

I'm working on a PCB that has shielded RJ45 (ethernet), RS232, and USB connectors, and is powered by a 12V AC/DC brick power adapter (I do the 5V and 3.3V step down on board). The entire design is ...
  • 1,593
121 votes
7 answers

Why does micro USB 2.0 have 5 pins, when the A-type only has 4?

What is the extra, 5th, pin on micro usb 2.0 adapters for? Here is an image with the different connectors. Most of them have 5 pins, but the A-type host only has four. (source:
  • 5,123
120 votes
9 answers

Tradeoffs when considering SPI or I2C?

What tradeoffs should I consider when deciding to use an SPI or I2C interface? This accelerometer/gyro breakout board is available in two models, one for each interface. Would either one be easier ...
119 votes
10 answers

Are solder fumes bad for me?

I do a fair bit of soldering (lead-free). Is breathing in solder/flux/paste fumes actually going to harm me? Are cheap fume extractors worth buying?
  • 28.6k
119 votes
7 answers

What’s the proper soldering iron temperature for standard .031" 60/40 solder?

I recently purchased a Weller WES51 soldering iron as my first temperature controlled iron and I'm looking for recommendations on the best default temperature to use when soldering. I'm using mainly ....
  • 4,275
118 votes
7 answers

What limits CPU speed?

I've recently talked with a friend about LaTeX compilation. LaTeX can use only one core to compile. So for the speed of LaTeX compiliation, the clock speed of the CPU is most important (see Tips for ...
  • 1,317
115 votes
5 answers

Difference between UART and RS-232?

Most of the time RS-232 and UART come together in serial communication theories. Are they both the same? From my readings I concluded UART is a hardware form of the RS-232 protocol. Am I correct?
  • 2,992
114 votes
4 answers

Why Are Ethernet/RJ45 Sockets Magnetically Coupled?

As the title says really, why do ethernet sockets need to be mag-coupled? I have a basic understanding of electronics, but mostly, I can't figure out the right search terms to google this properly.
113 votes
8 answers

Best One-Off DIY PCB Creation Technique

I have finally built up a lab to design electronics in. I have quite a few designs I would like to test. I have tried the printer toner/iron technique a few times but have found that I cannot create ...
110 votes
9 answers

Why does a resistor need to be on the anode of an LED?

Please be kind, I am an electronics nub. This is in reference to getting an LED to emit photons. From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons ...
  • 1,203
110 votes
6 answers

Are tantalum capacitors safe for use in new designs?

I've heard it suggested that "solid tantalum" capacitors are dangerous and may cause fire, may fail short circuit and are fatally sensitive to even very short over voltage spikes. Are tantalum ...
  • 143k
109 votes
6 answers

My linear voltage regulator is overheating very fast

I'm using a 5 V / 2 A voltage regulator (L78S05) without a heatsink. I'm testing the circuit with a microcontroller (PIC18FXXXX), a few LEDs and a 1 mA piezzo buzzer. The input voltage is aprox. 24 ...
  • 10.5k
107 votes
10 answers

What is negative voltage?

Just a general electronics question: What is negative voltage, like -5 Volt? From my basic knowledge, power is generated by electrons wandering from the minus to the plus side of the power source (...
  • 1,259
107 votes
5 answers

Can microcontrollers be run at arbitrarily low clock frequencies?

The datasheet for the ATTiny13A, for instance, lists Min frequency of 0 MHz. Does this mean the clock can be run at any arbitrarily low frequency with no ill effects? I'm assuming it draws lower ...
  • 28k
106 votes
3 answers

How do I calculate the required value for a pull-up resistor?

There are many tutorials that use a pull-up or pull-down resistor in conjunction with a switch to avoid a floating ground, e.g. Many of these projects use ...
105 votes
13 answers

Measuring feline capacitance

When I pet my cat, and then touch her on the nose, I get a little shock. Sometimes, when she walks up to something, her nose sparks and she jumps back and puffs out. I was wondering how I might go ...
104 votes
11 answers

VHDL vs. Verilog [closed]

VHDL and Verilog are some of the HDLs used today. What are the advantages and disadvantages of using Verilog or VHDL over the other?
103 votes
5 answers

Why are there 3 pins on some batteries?

Lots of new batteries (for mobile devices, MP3 players, etc) have connectors with 3 pins. I would like to know what is the purpose of this and how should I use these three pins? They are usually ...
  • 1,133
101 votes
6 answers

Ceramic caps vs electrolytic. What are the tangible differences in use?

A quick google around and all I seem to be able to find are people talking about the physics & the chemistry of the capacitors but not how this affects choosing which to use. Avoiding talking ...
  • 1,410
101 votes
10 answers

Why does a Tesla car use an AC motor instead of a DC one?

I was just watching a mega factory video and wondered why they use an AC motor which requires a power inverter instead of DC which may be powered directly from their DC battery? Introducing an ...
  • 1,121
100 votes
29 answers

What's the best way to store and categorise resistors/capacitors/ICs/etc?

I did a big cleanup of my collection of parts today and I now have a big pile of parts on my desk (the majority of which is resistors). My previous method of finding the resistor value I wanted was to ...
98 votes
5 answers

What is the difference between Flash memory and EEPROM?

Flash memory storage and EEPROM both use floating gate transistors for storage of data. What differs between the two and why is Flash so much faster?
  • 9,956
95 votes
10 answers

Why are there no 256-bit or 512-bit microprocessors?

In an 8-bit microprocessor its data bus consists of 8 data lines. In a 16-bit microprocessor its data bus consists of 16 data lines and so on. Why is there neither a 256-bit microprocessor nor a 512-...
94 votes
4 answers

What kind of components are black blobs on a PCB?

In low-cost mass-produced items I often run into black blobs of what looks like resin applied directly on top of something on the PCB. What are these things exactly? I suspect this is some kind of ...
  • 3,685
94 votes
10 answers

How to get more than 100mA from a USB port

I heard that the current limit for a USB port is 100mA. However, I also heard that some devices can get up to 1.8A from a port. How do you get past the 100mA limit?
93 votes
11 answers

Is there a correct resistance value for I2C pull-up resistors?

The datasheet of the 24LC256 EEPROM states that: The SDA bus requires a pull-up resistor to VCC (typical 10 kΩ for 100 kHz, 2 kΩ for 400 kHz and 1 MHz). I thought that any resistor with a kΩ value ...
  • 1,412
92 votes
4 answers

What are the different types of solder used for?

How do I know when to use lead, flux-core, lead-free, or any other kind of solder out there? Do you have any tips on solder gauge for specific applications?
89 votes
19 answers

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

simulate this circuit – Schematic created using CircuitLab My physics teacher said that the current through the resistor is 4A because each battery has a current of 2A if hooked up to the ...
  • 809

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