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Topic: Few advanced questions about Ethernet shield (Read 1 time) previous topic - next topic


Hi guys,

I would like to tell you that I'm not a noob. I am using Arduino Uno for quite some time and already successfully wrote several advanced programs (without help from others). So this is my first post, when need some help, because I didnt find satisfactory answers on the Internet ;)

My brother asked me to participade on hardware solution for highly specialized let me say "sensor site" for municipal use. Because work assignment was to be completely open-source sw and hw device, Arduino seems to be the simpliest and best solution at this time.
Each device will be arduino with few sensors, character LCD and ethernet shield. Every device will show its measurements on LCD and on specified local webpage but we need to know whether standard Ethernet Shield can do:

1.) send a web page (static html) not only locally (know that local broadcast is possible), but also directly to the Internet network (multicast) - to give access from anywhere, not just form local network.

2.) send "data stream"  - to  enable data to be fetched directly from one server (we dont want to parse html with servers...)

3.) whether it is possible to run local and internet broadcast at a same time (i.e. after delay but still in one program loop).

4.) how many pins (and which ones) are used by etherne :smiley-eek:t shield? Sorry, already found this somewhere but lost it again...  :0

I am asking because I dont have ethernet shield and never used it - we will purchase it with arduino in few days after all of last details will be checked .

Thanks for ALL answers ! 8)


1.) send a web page (static html) not only locally (know that local broadcast is possible), but also directly to the Internet network (multicast) - to give access from anywhere, not just form local network.

You don't usually "send" a web page.  Usually a web client (like a browser) connects to a web server (IP address and port) and asks for a particular web page.  When the web server is behind a NAT router this is made more difficult because the router needs to recognize the port number on the incoming connection and forward that request to the internal address of the web server.  Perhaps if the router supports "Universal Plug and Play" (UPnP) you can have the Arduino request the port forwarding. Otherwise you will need to configure port forwarding on the router.
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Everything you are talking about doing is possible, but you may want to consider your architecture carefully. Since you are looking at a network of sensors, you probably want each one to send its data to a central server which will collect the data and then make it available to whoever should see it.

Have a look at this:


Making an Arduino place http client requests is easy to do. You can do it with wired enet or wifi.


I would like to tell you that I'm not a noob.

Ok, have you studied the ethernet examples in the arduino IDE? Are you going to use the w5100/5200 chip based ethernet shields? If you are going to use a lot of pins, you may need an arduino mega. As to the questions:

1) An arduino web server can supply current analog input values to a web client. With the right setup, the client can be anywhere on the net.
2) The arduino web client can send data via a GET (and probably POST also) request to another web server.
3) The arduino web server can be both in a lan and from the wan. Not sure of your concept of a "broadcast".
4) Do your homework. 
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Have a look at this:

I know Cosm (former Pachube). It is nice, but it looks like it is not possible to display all my sensors in one map. So we will probably use own solution - currently the idea is to use OSM map background and a point layer with sensor stations in graduated colors according to their measured values and maybe additional page(s) with station details (description, history etc.).

The idea was, that the "customer" can display a local webpage from his own sensor station to check current values (this solution would eliminate the need of multi-platform desktop client GUI SW) while the station would always send the values also to the internet - to a server which would collect all the data feeds and display them in a map etc.


You could probably use the Google Maps API to do that easily.

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