le serial monitor de l'arduino me donne ceci:
connecting...
connected
HTTP/1.0 200 OK
Date: Fri, 31 Aug 2012 06:57:29 GMT
Expires: -1
Cache-Control: private, max-age=0
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Set-Cookie: PREF=ID=9d01d78c5d4d4ecd:FF=0:TM=1346396249:LM=1346396249:S=hBpUP915vl9gGPiR; expires=Sun, 31-Aug-2014 06:57:29 GMT; path=/; domain=.google.com
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P3P: CP="This is not a P3P policy! See http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=151657 for more info."
Server: gws
X-XSS-Protection: 1; mode=block
X-Frame-Options: SAMEORIGIN
(bla bla bla)
disconnecting.
tu es sur du dhcp chez toi ?
tu peux aussi essayer en mettant une adresse ip statique pour l'arduino:
par exemple
IPAddress ip(10,0,0,2);
IPAddress dnss(10,0,0,1);
IPAddress gw(10,0,0,1);
…
Ethernet.begin(mac, ip, dnss, gw);