やってみた

動作環境

Raspberry Pi2 + raspbian

pythonターミナルで上記の例をやってみた。
(API KEYは以下のものからすでに変更済み)

pi@raspberrypi ~ $ python
Python 2.7.9 (default, Mar  8 2015, 00:52:26) 
[GCC 4.9.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import httplib, urllib
>>> params = urllib.urlencode({'field1': 12, 'field2': 11, 'key':'BD6xM4sZEyT8'})
>>> print params
field2=11&field1=12&key=BX8D6M4U0GZE5KT8
>>> headers = {"Content-type": "application/x-www-form-urlencoded","Accept":  
...     "text/plain"}
>>> conn = httplib.HTTPConnection("api.thingspeak.com:80")
>>> conn.request("POST", "/update", params, headers)
>>> response = conn.getresponse()
>>> print response.status, response.reason
200 OK
>>> conn.close()
>>> params = urllib.urlencode({'field1': 3, 'field2': 2, 'key':'BD6xM4sZEyT8'})
>>> conn = httplib.HTTPConnection("api.thingspeak.com:80")
>>> conn.request("POST", "/update", params, headers)
>>> response = conn.getresponse()
>>> conn.close()
>>>

下記のようにプロットされた。
https://thingspeak.com/channels/77614