From: no@never.com   
      
   On Mon, 29 Jul 2013 19:59:22 -0400, j  wrote:   
      
   >On 7/27/2013 9:09 AM, amir.zawar@gmail.com wrote:> Hi Everybody,   
   > >   
   > > I am looking for a data logger which collects data from my "Solar   
   >remote site".   
   >   
   >If you go Arduino you can get an SD card/ethernet shield combo. There   
   >are a huge number of available shields including cellphone. Arduino has   
   >limited memory and interface capacity without a "shield".   
   >   
   >Arduinos have A/D's for data logging and there are "1 wire" temp sensors   
   >that connect to the digital inputs.   
      
   This kind of advice invariable comes from someone who's never actually   
   done it before.  As someone who designs this stuff for a living, let's   
   examine that advice a bit more.   
      
   It's true that the Arduino has 8 12 bit A/D converters of the   
   successive approximation type.  But there's more.   
      
   * Typically there are 3-4 bits of noise on the converters and/or   
   reference voltage so 8 bit data is the best that one can RELIABLY get.   
      
   * The input is 0-2.54 volts (unless one hacks in his own voltage   
   reference which brings in its own set of problems.   
      
   * The processor starts executing spurious instructions when the input   
   voltage reached about 2.6 or 2.7 volts.   
      
   * that channel is blown when the input reaches 3 volts.   
      
   * It  has practically no static or transient protection.   
      
   * The input impedance varies during the successive approximation so   
   the input must be driven by a low impedance source (op amp or   
   instrument amp).   
      
   * the input is monopolar.  Bipolar (AC) inputs make the processor very   
   unhappy.   
      
   The field signal for each channel must be scaled or amplified as   
   needed, zero offset, filtered, shaped, perhaps rectified and   
   conditioned for each input port.  This will cost many more dollars   
   than the Arduino itself and will require a vast amount of time to get   
   right.  Much more money, in fact, than simply buying the proper data   
   logger to fit the application.   
      
   The correct answer to the OP's question should be another question,   
   "What kind of physical data are  you trying to capture?  Most likely   
   volts and amps.  What else?  Thermocouple input?  Sunlight intensity?   
   Ambient temperature?  What range of temperature operation to you   
   require?   
      
   All that has to be known before any meaningful advice can be given.   
      
   John   
   John DeArmond   
   http://www.neon-john.com   
   http://www.fluxeon.com   
   Tellico Plains, Occupied TN   
   See website for email address   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)