Using the Arduino Ethernet Shield

[Leff]

http://www.element14.com/community/g...15-Arduino-e14
This is the first of a series of posts devoted to the (clever) usage of Arduino, with particular emphasis to scientific tasks. The content of these posts will also be available on my free publications on using Arduino for scientific purposes: Scientific Arduino Programming.

With respect to other similar posts, mine will not only show how to do something using Arduino: as a physics teacher I will explain why you are required to do that. In order to use any tool at its best, it is important to understand how it works behind the scenes.

As a physicist I often do measurements. Some of them can be done using an Arduino board equipped with some sensor. In fact, the advent of Arduino boards was a great advantage, mostly for those in need of cheap data acquisition systems for scientific purposes, like teachers in high schools or graduate students.

Most scientists do not take measurements, analyse them and show results in one single application: taking data can be a hard job that can keep your CPU very busy. Hence, in most cases, they just take as much data as they can out of the sensors and barely copy them as such on some mass storage device. Those data are then analysed offline using the best available tools that not necessarily coincide with the best tools for data acquisition. Presentation is a further step: once data have been analysed, the relevant results must be presented in the proper way and that job can be done with an even different technology.

In this post we show how to use Arduino to take data from some sensor and store them for further analysis. There are at least two very effective solutions: storing data onto files on SD cards or transfer data over the Internet to a remote location. The first solution is fairly simple, but data cannot be accessed during data acquisition; if the data taking persists for a long time you may prefer adopting the second solution.

Let's then assume we are going to use an Arduino board to get the values of few sensors during an experiment that lasts for a relatively long time. Moreover, imagine that the equipment used to take data needs to be kept in conditions such that it is difficult to have access to it (e.g. a dark room, or a climatic chamber). The only solution to get the data out of the system in almost real time is to use an Ethernet shield, i.e. an Arduino shield capable to connect to the Internet and exchange data over the connection.

In order for any device to connect to the Internet, the device must acquire a unique identity on the network: the IP address. The IP address (IP stands for Internet Protocol) of a device is a unique identifier composed, in the IPv4 version of the standard (the most commonly used), of four bytes, each of which can have a value between 0 and 255. Few of them are reserved internationally and, in particular, subnetworks whose first two bytes are 192 and 168 are non-routable, i.e. packets sent over such a network cannot go beyond an Internet switch. In other words they can only reach those devices on the same physical network. That's why devices in a home network usually have IP addresses like 192.168.x.y. The IP address of a device can be statically or dynamically assigned to it. In the first case, the device administrator tells the device its IP address: in this case the address is going to remain the same forever. A device not having a static IP address can ask for an IP address to any computer on the same network running as a DHCP server (Dynamic Host Configuration Protocol). Depending on the configuration of the server, available IP addresses can be assigned to the device randomly or based on the device identity.

Every physical device, in fact, brings a unique MAC (Media Access Control) address: a set of six bytes, usually expressed in the hexadecimal notation, as 5e:a4:18:f0:8a:f6. The MAC address is broadcasted over the network so that a DHCP server can choose if the request must be ignored, served using a randomly chosen address or with a fixed address.

Having an IP address in not enough for a device to communicate with other devices: data packets must reach a special device, called the gateway, that knows how to send data to the recipient. The gateway, too, must be assigned an IP address and its address must be known to the devices aiming to communicate with others.

IP addresses can be associated to strings composed of a host name and a domain name. All devices on the same network shares the same domain name, while host names are unique. A DNS (Domain Name System) is a device able to associate the IP address of any other device to its host name.

http://www.roma1.infn.it/people/organtini/publications/
http://www.roma1.infn.it/people/orga...ficArduino.pdf
http://ru.farnell.com/arduino/a00005...og-GOr-Arduino

[Leff]

Защищенный разьем RJ45

NEUTRIK NE8FDV-SE CONNECTOR, RJ45, JACK, 8P8C, 1PORT
http://ru.farnell.com/neutrik/ne8fdv...170315-Neutrik