For reading the temperature and humidity a SHT11 is used. Using https://github.com/practicalarduino/SHT1x reading data from the sensor is amazingly simple. The example code in the repository is all I needed.

The arduino has no time information. First I wanted to use NTP, but one HTTP client (the one sending the sensor data to the server) is enough difficulty for this problem. A friend of mine build a board similar to this setup: http://www.ladyada.net/learn/breakoutplus/ds1307rtc.html .

For initializing and reading the date/time information I use the code from http://www.glacialwanderer.com/hobbyrobotics/?p=12 .

Now I have date/time information for writing the sensor data to the SD card in the future.

The server side of my data logger is a very simple Flask site.

First version of the code:

from flask import Flask, request, abort
app = Flask(__name__)

import datetime

@app.route('/')
def index():
    return "nothing to see here ..."

@app.route('/input/', methods=['POST', 'GET'])
def input():
    if request.headers.get('X-ApiKey') != 'SECRET_API_KEY_SET_ON_ARDUINO':
        abort(403)
    if request.method == 'POST':
        log_to_file(request.data)
    return "OK"

def log_to_file(data):
    f = open('/tmp/arduino.logger', 'a')
    f.write(str(datetime.datetime.now()))
    f.write(': ')
    f.write(data)
    f.write("\n")
    f.close()