Questions tagged [usb]

USB is Universal Serial Bus. If your question relates to a specific chip, please mention it in your question.

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203
votes
7answers
186k views

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 ...
186
votes
8answers
31k views

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 ...
118
votes
7answers
20k views

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 ...
94
votes
6answers
170k views

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: wikimedia.org)
84
votes
10answers
146k views

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?
54
votes
2answers
21k 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?
53
votes
12answers
62k views

How to connect USB Connector shield?

How should I route USB Connector shield on PCB? Should it be connected to GND plane right where USB is placed, or should the shield be isolated from GND, or should it be connected to ground through ...
51
votes
8answers
97k 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 ...
50
votes
3answers
59k views

What is the ideal way to handle data pins D+ and D- on a USB power adapter to be compatible with fast charging on devices?

I have found that many USB wall chargers use a resistive voltage divider to set the D+ and D- pins to a specific voltage, usually between 2 and 3 volts. Other USB wall chargers short the D+ and D- ...
41
votes
2answers
12k 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]. ...
37
votes
5answers
15k views

Switch between 5V power supplies?

I'm designing a board that can be powered either by USB or an ATX power supply. They can both be plugged in at the same time, independently. I'd like the ATX to provide 5V if its plugged in, but ...
33
votes
2answers
7k views

How did USB 2.0 avoid collisions?

Looking at the pins of USB 3.0 receptacles, I can see that there are separate transmission and reception pairs, however for USB 2.0 there is only one "data" pin pair. How does USB 2.0 ensure that the ...
33
votes
10answers
56k views

How to build a USB controller having knobs, sliders, and switches

How does one go about building an interface for a USB device that allows interfacing pots, linear/log tapers, and momentary/toggle switches to a computer? If someone could give me a high-level ...
32
votes
7answers
179k views

How can I tell charge-only USB cables from USB data cables?

Like most computer hobbyists and programmers, I've amassed boxes of USB cables to connect USB, Micro-USB, and Mini-USB to chargers, computers, and gadgets. These cables are a mix of phone charger ...
31
votes
10answers
30k views

What are some smallest, cheapest microcontrollers with USB built in? [closed]

The cheaper, smaller, and fewer external components needed the better. AVR would be preferred, but anything with free SDKs is good.
29
votes
11answers
17k views

I'd like to learn how to make my own USB gadgets

I've been writing Linux character device drivers for other people's stuff for some time. I'd like to find a new hobby and the thought of making my own USB gizmos seems really neat. I would be ...
29
votes
2answers
76k views

What are the differences between USB and RS232?

Can someone tell me why people use either USB or RS232. They are both serial ports, right? And I understand that USB is much faster (especially USB3.0) but if people wanted too I'm sure they could ...
29
votes
3answers
17k views

How does USB Type C handle reverse polarity

The new USB Type C connector doesn't have a physical reverse polarity protection anymore. You can plug it in any way you want on both ends, there is also no A and B end anymore, it's all the same. So ...
28
votes
2answers
3k views

Why are the contacts for the Data lines in USB A and B plugs shorter than the contacts for Ground and Power?

I was reading up on USB connectors on Wikipedia and I've noticed that the contacts for the data lines (D+ and D-) are shorter in both the Type A and Type B plug. What could be the reasoning behind ...
28
votes
3answers
18k views

What do the 3 symbols (circle, square, triangle) in the USB Type-A plug represent?

What do the 3 symbols (circle, square, triangle) in the USB Type-A plug represent? Is it power-/data-related notifications or just universal identification for USB?
26
votes
5answers
95k views

Just chopped a cable, is red power, black ground?

I've just chopped a usb to micro-b usb cable. There are 4 small wires inside Red Black White Green Isn't it universal that Red is power and black is ground?
26
votes
2answers
11k views

Connectorless USB on a PCB

I would like to make a board which can be plugged directly into the USB port of a computer, instead of using a separate male "USB-A" connector. I have seen this system used for very small USB memory ...
25
votes
4answers
6k views

USB Shield. To ground or not to ground?

I have been given a device at work to do some testing on. Basically an IC is becoming obsolete so I need to test a replacement part. Upon redoing the ESD checks, the device failed. I checked the ...
24
votes
8answers
10k views

Why do USB connectors only fit one way?

Why do USB plugs only fit one way into USB ports? Forgive my ignorance, but there are several types of plugs that are "omnidirectional" and do not have to be oriented a certain way to fit into the ...
24
votes
8answers
38k views

How do USB charging and “smart” charging ports (e.g. Anker's PowerIQ) work?

Software engineer with a hobbyist understanding of EE here. I've noticed lately lots of claims from producers of USB battery packs that their ports are "smart" and "identify the device" to "deliver ...
23
votes
2answers
3k views

How do I make the Fairchild FSA9280/FSA9480/FSA880 BOOT pin trigger? (Samsung Galaxy S)

this is a bit of a long shot but I'm hoping someone has access to the full data sheet for one of the chips listed in the title, and can tell me what combination of VBUS_IN and resistors on ID_CON will ...
22
votes
2answers
37k views

How does a USB C port provide the power to charge laptops?

I've heard about laptops such as the new Chromebooks that are charged via a wall charger that connects to a USB-C port. I'm quite happy that this will supposedly standardize laptop chargers but I'm a ...
22
votes
2answers
1k views

Solution for adapting to USB current draw limits?

Summary: I'm setting up a USB-powered Li-ion charging circuit and would of course like to draw the maximum charge current possible situationally -- but also want to ensure I don't violate the USB ...
21
votes
3answers
3k views

Pass USB 3.0 connection through D-SUB connector

I need to pass a USB cable through a vacuum chamber wall, for which we have only D-SUB passthrough flanges available. So I cut a USB cable in half and soldered a D-SUB connector to each half. For USB ...
20
votes
5answers
28k views

Why does USB have Vcc=5V and high=3.3V?

I am thinking about adding USB support to a device of mine using V-USB. From what I read there and on other sites USB seems to have only 3.3V as a high level on the data pins, whereas the voltage ...
20
votes
4answers
12k views

What is the best USB transfer type (bulk, interrupt, Isochronous Transfers) to be used for implementing a USB oscilloscope?

I want to build a USB oscilloscope. I was reading about different USB transfer types. Which transfer type is best to transfer the collected ADC samples from a USB oscilloscope to a PC? Below are a ...
20
votes
2answers
72k views

What exactly are the differences between a USB host and device

Came across some doubts: What exactly are the differences between a USB host and device? Is it just that who powers the bus? When two devices connect how the device say "hey I will be the host and ...
20
votes
3answers
80k views

How to transform 5V into 12V?

I would like to transform 5V 500mA (from USB power) into 12V with a few cheap components. Is this possible with the help of some generic parts (and not with the help of some expensive transformer, ...
20
votes
2answers
22k views

How does an FTDI chip work?

Someone asked me the other day how an FTDI USB to serial UART works, and I realized I didn't know. I looked at the datasheet for the FT232R and the block diagram didn't really help me. Can anyone ...
19
votes
6answers
3k views

Why would a buck converter IC fail and blow up?

I have a deployed design in which we are experiencing a high (~4%) failure rate in the 12V to 5V step-down buck converter portion of the PCB. The buck converter's role in the circuit is to step down ...
19
votes
3answers
15k views

How to limit inrush current?

I'm designing a device powered from USB. The device uses FTDI FT2232 chip for USB connection. Upon a command from a computer FT2232 chip should enable power via a MOSFET switch to rest of the circuit. ...
17
votes
5answers
27k views

What is the simplest and cheapest way to interface with USB?

If I wanted to make a simple device that communicates with my computer, say maybe a switch that could mute my computer when turned on and off and plug it in via USB, what would be the cheapest and ...
17
votes
3answers
6k views

Understanding USB Inrush Current Requirements

In relation to a previous question, I'm trying to understand the USB 2.0 requirements for inrush current. I understand the basic idea, but a few details are still unclear to me. The specification ...
16
votes
3answers
3k views

Why is USB Type-A to USB Type-A never used?

I was wondering why almost all USB cables that exist are USB-A to (Micro-USB | USB-C | USB-B | etc.) Why was USB-A to USB-A not a popular thing? Is there a technical reason this cannot work?
16
votes
2answers
5k views

USB signal routing - Swap data lines using vias?

I'm making my second USB design, but the D+/D- pins on the MCU (atemga16u2) aren't in the right order for the micro B connector. What's the best practice for routing these to go the right way? My ...
16
votes
2answers
10k views

Does a self-powered USB device have to connect to VCC from the host port?

A self-powered USB peripheral provides its own power, so is it okay to connect just D+, D- and GND to the host port, or do you always have to connect +5V as well, then wait for the negotiation phase ...
15
votes
4answers
17k views

Are Common Mode Choke Coils needed on USB?

I was looking over the schematic for the GumStix Palo 43 and noticed they used a common mode choke coil on the data lines coming in from USB. I understand how this design can help remove noise ...
15
votes
2answers
1k views

Where exactly is the USB spec that explains what to do when the cable is first connected?

So I know about the USB 2.0 spec located at the USB.org site. I am a little lazy and impatient. Can someone tell me where to go to find out exactly what is expected of my peripheral device when the ...
14
votes
5answers
19k views

Crazy homebrew 500 MHz 1 Gs/s oscilloscope possible?

I was reading USB scope probe - request for comments and ideas, and it got me thinking. What I'd really like is a very high performance oscilloscope, one which would cost $10000 or so. Surely many ...
14
votes
8answers
3k views

RnD on an EEG, Help required, what op-amp?

this is my first post, and I need some help/advice finding the right integrated circuits. I'll start by describing the project background a bit. I've received a fellowship to develop an open source ...
14
votes
2answers
14k views

USB to GPIO module

I'm working on a project which involves having users press buttons on a webpage which the server needs to send onto a microcontroller in the form of a GPIO signal. The only ports available on the ...
14
votes
2answers
10k views

Serial newbie: why can't I just hook the wires up?

I'm trying to transmit from an ATtiny85 to a PC using Arduino-esque code over a USB-Serial converter without understanding very much of anything. I was shocked and appalled that it did not work. I ...
14
votes
1answer
9k views

How to select a good Ferrite Bead

I am building a USB project and I want to use a Ferrite Bead in the USB 5V rail. I am looking for 1206 Ferrite Beads. How to select them properly? Which impedance at 100MHz is a good one?
13
votes
5answers
3k views

Why does USB only use 2 lines for RX, TX instead of multiple data lines? [duplicate]

Wouldn't it be faster if there were multiple data lines (say 8) to transmit/receive data (say sequential bytes) instead of using a single line to transmit sequential bits?
13
votes
1answer
18k views

How critical is the layout of USB data lines / how does my layout look?

I'm laying out the USB data lines on my board at the moment, and I'm just trying to get an idea of how well off my design is gonna fare. Here are the particulars: 4 layer board (from the top: signal,...