Ethernet is more approachable than you might think!

Using Ethernet to interface flight controls or instruments to your computer may seem to be an expensive overkill.  Ethernet is generally associated with high performance communication between workstations and servers. But if you build a complex, highly instrumented simpit, you may well need a wide, low latency data pipe to assure high responsiveness.  Fortunately, Ethernet hardware and software has experienced  price-performance improvements similar to other computing components, and costs now look surprisingly attractive.  

A bit of embedded Ethernet background

It was in part a desire to give appliances and vending machines a web presence (or something very similar) that has driven these developments.  I seriously doubt that our refrigerators will ever email the grocery store to order food for us, but there are substantial benefits to be had in other areas.  

Consider the way vending machines are serviced.  Most require a visit on a regular schedule regardless of how much product remains in them.  I say "most" because a substantial number of Coke machines in the southeastern US electronically communicate their sales to the warehouse.  The result has been a profound improvement in the efficiency of servicing those machines, coupled with a substantial boost in profits.  

There are a number of available embedded Ethernet products

Coke did not use Ethernet technology*, but Ethernet technology is a viable alternative.  The financial success of Coke's project is a factor that encourages Ethernet product vendors to enter this market. To do so, they have developed simplified, low cost Ethernet interfaces incorporating their own TCP/IP stacks.  With quantity prices as low as about $30US, these little units deserve a look.

SitePlayer is one such device.  It's a daughter board with an area of about 1 square inch.  It communicates through both an Ethernet port and a serial port.  Not the speediest of the batch, but probably not a bad match for things like radio stacks and enunciator panels.  This is a $30US item.

Embedded Ethernet offers what looks like a somewhat more powerful board.  With Ethernet on one side and a 16 bit parallel port on the other, it should support higher bandwidth. The site has example circuits and code showing how to interface the product to both PIC and Atmel micro controllers.  This board sells for $70US.

TINI stands for Tiny InterNet Interface.  It was developed as a reference design by Dallas Semiconductor (now part of Maxim).  It's a board the size of an old style 72 pin SIMM incorporating a micro controller,  SRAM, flash ROM and interface circuitry. In addition to a 10baseT Ethernet port, it has CAN, 1-Wire and serial ports as well as straight digital I/O lines.  It comes with a development system programmable in Java. The board costs $50US, though for about $20US more you can get twice the SRAM. Extensive on-line resources support this product.  Additionally, it is covered in detail in the book Designing Embedded Internet Devices by Dan Eisenreich and Brian DeMuth.

Here are a few information resources

Admittedly, adding Ethernet interfaces to simulator hardware would not be a project for someone with little experience, but with the availability of these and similar developer kits, it's certainly a possibility.  As with every interfacing project, there are both hardware and software aspects to be considered.  The developer's kits supply information about programming the little beasties.  Communicating with them once they are properly programmed requires using sockets.  If you're running a windows machine, you already have winsock.  Writing C or VC++ code to create and open a socket is fairly straightforward.  You can get on-line information here, and check out Comer's encyclopedic book series, Internetworking with TCP/IP volumes 1-3 for details about internetworking in general.

Jan Axelson has a new book out. Embedded Ethernet and Ethernet Complete covers, well the title kind of says it all. Get the details from her site. I have not read this book (yet), but having read some of her earlier work I expect it to be a good addition to the bookshelf.

* Coke's solution is based on SS7, one of the signaling system technologies that manages wireless telephone networks in the US. SS7 was designed with substantial excess capacity relative to the task at hand to guarantee that the control structure could not get bogged down by heavy usage of the "audio" channels.  Some of this excess capacity can be leased for other uses. SS7 sends short packets only, and its absolute, aggregate capacity is limited, so it's most suitable for low bandwidth applications.  Still, it's more than adequate for a coke machine to report sales, and for a stolen car to call for help (LoJack).

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