Questions tagged [ethernet]

Questions about the electrical implementation of Ethernet; ask another Stack Exchange for software or protocol questions. Specify the speed as 10/100BASE-T is somewhat different from 1000BASE-T, apart form the speed. Those are copper standards; Ethernet over fiber optical cable is also defined.

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101
votes
6answers
42k views

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 ...
17
votes
5answers
60k views

Difference between Hz and bps

Does Hz and bps mean same? Can a signal be transferred at rate of say Mbps on a channel bandwidth of few Khz?
10
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4answers
25k views

Connecting two Ethernet PHY without magnetics?

In a (tentative) new design I want to connect two 100 Mbit/s Ethernet PHY similar to LAN8270a, separated by few inches on the same PCB, with same ground plane (but different power supplies). I have ...
13
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2answers
6k views

Ethernet Without Magnetics?

How / can you connect Ethernet devices together without magnetics? How do you wire it up? What sorts of practical limitations are there on doing this? To clarify, I'm not trying to connect two ...
99
votes
4answers
53k views

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.
13
votes
4answers
7k views

Building a passive ethernet hub with anti-parallel diodes

I've found several guides online on how to build a passive ethernet hub, the design is always the same: I'm wondering what each of the 2 anti-parallel diodes do? For both positive and negative ...
47
votes
20answers
78k views

What is a good microcontroller for Ethernet applications?

What is a good microcontroller for doing Ethernet applications? Or do I just need a good Ethernet library to connect with an Ethernet MAC/PHY?
7
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4answers
13k views

Why is Bob Smith termination for Ethernet recommended if it's wrong?

I came across this article today (more detailed paper), which claims that the widely recommended Bob Smith termination (75-ohm resistor + 1000pF to chassis GND) may not be ideal (or correct). If this ...
23
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4answers
24k views

Very Long Distance Ethernet connection for Internet and other data (2000 feet)

I am building a house. It's located about 2000 feet away from the nearest Internet cable. I had to run our electrical service underground the whole way, and have already installed a conduit for ...
8
votes
3answers
8k views

How does “bidirectional” transmission on gigabit ethernet work?

I was reading about the various twisted pair protocols, being distracted by the marvels of Wikipedia when I went to look up the way to wire a connector. And I'm wondering how it can transmit in both ...
5
votes
1answer
253 views

What ultimately determines the speed of electrical media

I have heard several myths about this. Some have said "thicker wires mean faster speed" which I don't believe. Others have said different voltages and others have said higher frequencies. Take Coax ...
41
votes
10answers
25k 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 ...
15
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7answers
4k views

What if there are an odd number of twists in a twisted pair cable?

I am not an electrician, or a student of the field. I am a Network Engineer with a curiosity bug and that has recently taken me to exploring cabling and Twisted Pair specifically. I say this to plead ...
9
votes
2answers
8k views

Effects of impedance matching between 50 and 75 Ohm coaxial cables for 10 Mbit/s, Manchester-coded signals (20 MHz)

TL,DR: This is quite a bunch of text because I have included plenty of background info. However, there will finally be a good, and precise question: Should I use an impedance matching network when ...
9
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2answers
7k views

Ethernet: how important is the magnetics topology?

I have some Ethernet issues with a set of boards (6/10 are bad). They're possibly just assembly house mistakes... but I'm very concerned about my magnetics jack. I could have sworn I saw a example ...
8
votes
2answers
10k views

Length Matching Differential Pairs

I am routing a PCB with an Ethernet connection and I am having a bit of trouble deciding on how best to route the TX and RX differential pairs. I have done the impedance calculations to figure out the ...
5
votes
3answers
10k views

Why is Cat5/Cat5e Ethernet cable rated 100MHz?

As the questions says, is there any specific reason why Ethernet cable is rated 100MHz? For a 100Mbps Ethernet the data rate is 100Mbps, and the baud rate is 125Mbaud, because of the specific line ...
4
votes
4answers
6k views

Current over ethernet?

It seems that the voltage over ethernet ranges from 2 to 3 volts. How much current typically runs through the wires? I tried Googling with no success. I ask this because I'm looking for components ...
2
votes
2answers
4k views

2kV capacitor on ethernet?

I'm building the circuit of this article: C7 is rated 1nF 2kV. Is this right, does this capacitor need to be able to handle 2kiloVolt? Why is that? Is ethernet dangerous?
11
votes
1answer
5k views

Bob Smith Termination with POE

I'm looking into doing a Bob Smith termination for a Power over Ethernet (POE) PSE. The TI app note shows the following termination: But all of TI's reference designs (and later figures in the same ...
4
votes
2answers
2k views

Passive POE: Need 5V @ 2A at the destination

Having a bit of trouble finding the right information on google, and I'm worried I might fry some cables so I thought it best to ask some far more knowledgable than myself. I want to connect 2 or ...
4
votes
5answers
7k views

Ethernet RJ45 interfacing with microcontroller

I am working on a project, (still in the nascent stage) where I have to implement a serial communication interface and an Ethernet interface. I tried to find out as much as I can and got the following ...
19
votes
8answers
33k views

Communication between multiple microcontrollers

I'd like to start implementing a system consisting of N microcontrollers (N >= 2 MCUs), but I would like to know the possibilities to let them communicate one with the other. Ideally, (N-1) ...
20
votes
8answers
13k views

Cheapest way to add wifi to a project [duplicate]

I need low power wifi for a not-very-data-intensive application. What modules or chipsets should I look at? Other than low cost and low power, I have no restrictions. The cheaper the better. This ...
13
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3answers
14k views

Ethernet Layout Guidelines

I'm working on a DC jack powered Ethernet design and I've downloaded many Ethernet Layout guidelines from many semi vendors with varying recommendations. I've read app notes recommending almost every ...
16
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1answer
2k views

Reasoning behind Ethernet pair order

An Ethernet connector seems to use a surprising choice of signal placement in its RJ45 connector. Does anyone know the reasoning behind: The decision to make pair 2 straddle pair 1? Why Ethernet uses ...
13
votes
3answers
6k views

How to Connect USB/Ethernet Shields to Chassis or Digital Grounds

I have a PCB with a few USB and RJ-45 Ethernet connectors on one side. I'm quite confused as to how exactly I'm supposed to be hooking up the SHIELD pins on them though. This is for a host device ...
5
votes
4answers
15k views

How to specify 100 ohm impedance on a pcb gerber

I've been using Altium for several years when I've needed to designed boards. However it's all been for simple analog designs and never anything too technical. I'm now trying to take a jump into a ...
4
votes
1answer
3k views

How to route Gigabit Ethernet, remote PHY or remote RJ45 connector?

I need to design a 10/100/1000 BASE-T “backplane” board that contains multiple PHY outputs from Ethernet controller chips. On the board ,the LAN specifications are very strict in regard to how the ...
3
votes
3answers
25k views

Sending audio over ethernet

I am trying to send audio from a microphone such as this over Ethernet to a computer. My first idea was to connect the mic to an arduino's ADC and send the data using an ethernet module such as the ...
1
vote
3answers
2k views

Is there another Arduino ethernet module besides the “Arduino Ethernet Shield”?

On the official Arduino website only the Arduino Ethernet Shield is referenced for Ethernet programming. Are there any other modules for Ethernet on the Arduino?
8
votes
3answers
14k views

How do network devices detect whether an ethernet cable is connected?

I have a bit of kit with an FPGA on it which includes an ethernet adapter. I'm trying to diagnose why it's not working and while I do that I've noticed that with an ethernet cable connected to my ...
4
votes
3answers
15k views

How to avoid SD Card and W1500 SPI mixup on the Ethernet Shield?

In an answer Kevin Mark points to a solution/reason for the usage of the Ethernet shield together with the SD Card. The documentation says that SD Card and the Ethernet chip both share the SPI bus and ...
8
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3answers
4k views

Schematic Critique: Phy interface with RJ45/Magnetics

I'm working on my first major schematic design and would really appreciate some feedback on the analog side of the 1000BASE-T Ethernet interface. I'm mostly concerned about the analog line termination ...
7
votes
1answer
30k views

How do Tx / Rx cable pairs work in an Ethernet cable?

This question will be a simplification as I lack the proper knowledge. Lets suppose we want to send a signal over the network. We will use this scheme as this is hopefully how the signals are send ...
7
votes
3answers
3k views

Ethernet.begin() only works with SD Card removed - why?

When I run this code on my W5100 Ethernet Shield: byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; void setup() { Ethernet.begin(mac); } it only works ...
6
votes
1answer
4k views

Caculating baud rate of Ethernet per wire

I'm trying to find the answer to what should be a simple question. How do I calculate the physical rate bits are transmitted on an individual Ethernet wire? I am interested specifically in 100 Mbps ...
2
votes
2answers
5k views

When connecting to Ethernet through ENC28J60, why use ATmega88 instead of ATmega8?

I know the general differences between ATmegaX8 family (ATmega88, ATmega168, and ATmega328) and the ATmegaX family (ATmega8, ATmega16, and ATmega32). But I'm confused, as when I intended to work on a ...
2
votes
3answers
857 views

Wired AND Wireless Embedded Ethernet Project

Hey guys, I would like to design a device that is capable of connecting to a PC via WiFi or a wired connection (ideally Ethernet as well). I would like for it to be possible for a wired connection to ...
20
votes
3answers
1k views

Do magnetics connectors exist?

Conventional connectors, where the plug and socket have metal parts which touch, suffer from the following problems: Limited mating cycles or expensive plating. Impedance mismatch (relevant for high ...
9
votes
1answer
2k views

Ethernet: distance from PHY to magnetics

I am confused as to the preferred placement of Ethernet PHY and magnetics. I thought that in general, the closer the better. But then SMSC/Microchip app note (http://ww1.microchip.com/downloads/en/...
7
votes
4answers
2k views

Ethernet Without a Switch?

How do you wire up Ethernet electrically without a switch? An approximately equivalent phrasing of this question would be what is going on electrically inside an Ethernet Hub? To clarify, I'm not ...
6
votes
1answer
3k views

How does Ethernet magnetics work?

If you refer to Figure 14 of http://www.analog.com/media/en/technical-documentation/application-notes/EE-269.pdf. There are 2 transformers on each data pair. Can someone help explain how they work? ...
5
votes
5answers
5k views

Implement send-only (one-way) Ethernet cable

I want to build a unidirectional comminucation. In transportation layer of this device, it needs a one-way media to send data from side A to side B. All commercial products use SFP. I tested some SFP ...
5
votes
6answers
25k views

Is there any way to send serial data over physical ethernet layer with no encapsulation?

I wonder if I can use the physical ethernet layer like a serial port. Is it possible? The case would be reading signals with an electronic device without dealing with networking headers.
3
votes
1answer
510 views

Are there any special internal Ethernet connectors other than RJ45?

I am working on the board that suppose to have 1 GbE port (10/100/1000BASE-T). Looking at connectors all I seem to find is standard RJ45 connector. However in my design the board itself is not ...
3
votes
4answers
4k views

Smaller alternative to RJ45 Ethernet connector

I am trying to minimize space usage for an enclosure that holds 48 boards with a RJ45 connector for Ethernet communication on each board. The boards work well with 10BASE-T (2 pairs) connection to a ...
3
votes
4answers
22k views

Arduino Ethernet shield: it just won't work!

I have an Arduino Ethernet shield on top of an Arduino Mega2560 and have connected the Mega2560 through serial to my laptop and through the UTP port on the Ethernet shield to my router. I've tried ...
3
votes
2answers
353 views

Difference between link-aggregated 10x10GbE and “True” 100GbE

I'm reading on 100G Ethernet and came across this article by ADVA. On page 2, top paragraph (before "Spectral Efficiency"), it compared link-aggregated 10x10GbE and a "true" 100GbE and says A true ...
2
votes
3answers
6k views

Strange I2C behavior: sometime it works, some time it doesn't

I am using Arduino Ethernet with PoE and Arduino Uno boards. In recent days I implemented a working I2C bus by using the Wire library and all it seemed almost to ...