October 26th, 2010

Magnetic-Less Ethernet

I wanted to test if its possible to have a magnetic-less ethernet connection for an upcoming project. Why magnetic-less? you might ask, well space & weight is critical for my application and since both devices will be present on the same PCB, why not skip the magnetics and reduce space & weight. I have to admit it was allot easier than I imagined it would be. When I first thought about it I imagined I would need to simulate the impedance of the transformer with some inductors, this way before I did any reading on the subject.

Thankfully I had a friend who helped me with some network switches from his junk box. The switches were running ok but its clear that they once had some reliability issues which got them into the junk box, but it was enough for my little experiment. I decided to use the following configuration to test the magnetic-less connection:

  • both switches will have the transformers removed from one of the ports.
  • computer1 connects to switch1 with standard connection.
  • switch1 connects to switch2 with magnetic-less connection(no transformer).
  • computer2 connects to switch2 with standard connection.

After the setup is made and link is up I would ping computer2 from computer1 and if the link is ok the result should be obvious.

network switch test configuration

Now, at this step I still haven’t done any reading on magnetic-less ethernet connections, so I took the bad choice of connecting the two magnetic-less ports wire to wire, “wire coupling” 🙂 . I knew i had slim chances to make it work, but I said nothing can go wrong. I hooked the two ports, and nothing happened, no link, no LED turned on. Probably somewhere in this process I damaged the two network switches(RTL8309SB) because they were both working before I did surgery on them, and they were both not working when I finished the surgery 🙂 So directly coupling the two interfaces is a bad idea, it should of ringed a bell the first time I thought about it but it didn’t, I learned it the hard way.

two 10/100 ethernet switchesremoved magnetic transformer from ethernet lineremoved magnetic transformer from ethernet line

This is where I knew I had to do some reading on the subject. Luckily every manufacturer of ethernet interfaces has an application note on how to couple them magnetic-less for exactly the same situation that I have: both chips on the same pcb. I picked up another 2 switches and opened them up. Since they both had Realtek controllers I used this application note from Realtek. The app note provides a simple solution, capacitive coupling.

schematic for magnetic-less ethernet

I got to work, once again I removed 1 transformer from each network switch but this time I used capacitive coupling. I soldered wires to where the transformer used to be and I connected those wires to a mini breadboard. The resistors+capacitor pair which sit between the lines on the schematic are still on the board, they’re needed with or without the magnetic transformer. All I had to add was one 0.1uF capacitor on each line. I didn’t even used the pull-up 1.8V as suggested by the app-note. I did the connections as mentioned above, the link activity LED’s signaled immediately, I assigned the computers some ip addresses and success I had the link up & working in no time. I only did a ping test which resulted in under 1ms replies. Perhaps I should of tested the bandwidth too, but I don’t think it suffered from the change.

wires going from the port to the breadboard and on to the next switchwires going from the port to the breadboard and on to the next switchremoved magnetic transformers and replaced with capacitive couplingless than 1ms link with magnetic-less ethernet link


Now that I know its working I can save space & weight by implementing the real thing.

Beverage Temperature Regulator

There’s nothing like an ice-cold drink on a hot summer day, is there? Especially if you’re a beer-loving dude with some free time and some hardware skills.

A fairly simple and fun project, the “Digital Thermostatic Beer Refreshment Regulator” (as entitled by its author) is based on an Arduino and a temperature sensor that control the temperature of the liquid inside the refrigerator (i.e. beer). The Arduino is actually a Freeduino SB and the temperature sensor is a LM35DZ. The beer regulator also possesses a NTE RS1-1D4-21 solid state relay to trigger 5v voltage to manage the amperage of the refrigerator.

The temperature is displayed on a SLCD162 MeLabs serial LCD Display which only uses 1 pin of the Arduino microcontroller. Other parts include some 10k and 100k resistores, pins, connectors, wires and plex-glass for the LCD stand (you can find a detailed parts list in the link). The code is written in C and it can be easily modified to adjust turning of the whole device ON or OFF to match your desired temperature of the beer. Plans for rewriting some of the code to get a more precise temperature are on the way. Also, a more complex display could be added to the project quite easily, since the current LCD is connected using an ethernet jack with Cat5 cable.

Now, I’m pretty sure you can do all these things with a common refrigerator that has a LCD display on the outside and a front panel to set the temperature, so it’s hardly a world changing project. Further more, you don’t risk getting your fingers burnt with the soldering iron or having your kitchen fill with cold beer (maybe that wouldn’t be such an issue to some, but still). However, if you’re a do-it-yourself kind of guy and want to make your own cold beer apparatus, then you can try this one. Salute!

Beverage Temperature Regulator: [Link][via]

January 19th, 2009

Ethernet relay board

Ethernet relay board

There many devices which can be controlled trough relays, like light bulbs, pumps, motorized doors, and the list can go on. Most of the relay boards available on the web are based on the serial interface, this has some drawbacks: limited distance, about 15meter based on the RS232 standard, and the new generation of motherboards lack this port. The presented board has ethernet interface using the ENC28J60 and the PIC18F4680, it also has a Real Time Circuit with battery backup, the ethernet interface beside its speed has a major advantage, the RJ45 contains a coupling transformer which is used to galvanically isolate the local electronics ground from the bus, this doesn’t mean that it will support a 230 common mode voltage, but offers protection to a certain limit.

The ethernet interface shows its full potential when comes along with a webserver, fortunately the author thought this to, he developed a simple web server which runs on the PIC, this way you can control the relays trough your network or even the internet.

Ethernet relay board: [Link]

November 19th, 2008

Ethernet via Arduino

Ethernet via Arduino

For Arduino fans this is  great news, now its possible to extend the functionality of the Diecimila board with ethernet shield. The board is built using the w5100 chip from Wiznet, so no need to implement the IP stack.

To connect to your LAN, all you need is to configure the MAC address, the IP and plug the cross cable into the RJ45.

There is offcourse available some demo application, with server/client possibility for easy startup.

This board offers the possibility to explore the TCP/IP networking with a simple and affordable hardware and free software tools.

Ethernet via Arduino: [Link]

April 3rd, 2008

DIY VGA cord

 DIY VGA cord with cat5 ethernet cable

I don’t entirely recommend using this option for a VGA cord, because the cable used by the author the CAT5 ethernet cable is not shielded and doesn’t have the same properties as a native VGA cable. But this solution works too, so if you’re in desperate need of a VGA cord and can run the store an get one, you could approach this instructable.

DIY VGA cord: [Link]

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