[lug] Ethernet Enabled PLC/Linux Microcontroller

[Nate Duehr]

On Jul 31, 2009, at 7:27 AM, Swavek Skret wrote:

> I need to control a hardware unit that does not have a standard  
> interface (ethernet, RS-232, etc) but simply provides a binary  
> voltage to flag that it functions correctly or not. I am considering  
> using an ethernet enabled microcontroller with Linux OS ideally.
>
> If anyone has related experience and would like to share or  
> recommend a particular hardware I would appreciate it.
>
> Thanks,
> Swavek


Full blown embedded Linux is probably overkill.  Any microcontroller  
can be made to do simple voltage monitoring and spit out serial  
information to a connected PC, phone line via a modem, whatever...

Microchip and Atmel are the most popular for "hobby" projects, and  
there's thousands of designs available for commonly used ones on the  
Net.

Both have free Assembly and C programming language support, but you do  
have to learn a bit about how to program "at the hardware level", so  
to speak.  A month or two of study will yield a lifetime of cheap,  
virtually bullet-proof hardware control solutions.

There are also development kits for both major chipsets that make  
programming them a breeze in languages like BASIC and similar.  Even  
some GNU/GCC projects for both, if you're willing to put up with the  
usual crappy open-source documentation and brain-damage.

The forums at Microchip.com or avrfreaks.net are good starting points,  
if you already know basic electronics including Ohm's law and how to  
solder, both of which are pretty basic -- and there's plenty of "DIY"  
ways to learn both on the Net.

There's no need to use an entire OS like Linux, when a few lines of C  
code compiled into machine language by a free compiler and dumped into  
a chip will do the job.  The logic involved is basically 1 for on, 0  
for off... something we all know, and the electronics involved in  
seeing if a device is "on or off" is not much more difficult than the  
circuit for a typical table lamp.

Going all the way to Linux on a chip will be more "fun", but WAY more  
expensive both in the short and long term, unless you're only doing  
ONE of these.  I do suggest hunting the web for microcontroller  
circuits to do such a thing.

Other "medium difficulty" options might be to use something like a  
PicAXE or Arudino where a hardware engineer has already developed the  
board, the layout, defined the chip(s) needed and provided a  
rudimentary real-time "OS" FAR better suited than Linux to handling  
the little (inexpensive) chipsets.

http://www.rev-ed.co.uk/picaxe/picaxe.htm
http://www.sparkfun.com/commerce/categories.php?c=103

Etc etc... the possibilities are endless.  But Linux on the chip  
certainly sounds like SERIOUS overkill when a single chip can do the  
job...

--
Nate Duehr
nate at natetech.com

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