XPost: sci.physics, sci.electronics.design   
   From: earlcp@idirect.com   
      
   dave.harper@gmail.com (David Harper) :   
      
   > I'm interested in developing a sun sensor (or maybe a horizon sensor)   
   > for a low-cost, amateur, high altitude project.  However, I'm having   
   > some difficulty determining the best setup for the sun sensor.  The   
   > majority of the sensing will occur over 20km (about 65,000 ft), so the   
   > effects of radiation from the sky can be considered minimal.   
   >   
   > I was considering two methods:   
   >   
   > The first involves 5 photocells mounted at 90 degree angles to each   
   > other (one pointed vertically), with a light shield mounted below   
   > allowing a half-angle of around 60 degrees (i.e. blocking the light   
   > from the earth, so long as the sensor is 30 degrees from vertical or   
   > less).  Measuring the resistance of all 5 photocells should yield   
   > (with the appropriate calculations) the position of the sun wrt the   
   > photocells.  One concern I have about this method is the large   
   > variation of performance of photocells (regardless of having the same   
   > part number), and would probably require some careful calibration.   
   >   
   > The other method is to have a sheilded field of, say, X by X   
   > photocells and a single opening centered over it.  This method is much   
   > more "coarse", expensive, and harder to make, but less suseptable to   
   > non-solar radiation.  I'm aware that most "non-amateur" sun sensors   
   > use CCDs instead of photocells, but I believe that is a little beyond   
   > my experience (and budget).   
   >   
   > Does anyone else have knowledge of other techniques involved in sun   
   > sensors?  Are any photocells or other light sensors better (or more   
   > precise) than others?  Also, are there any wavelength filters I should   
   > consider? Any info is greatly appreciated!   
      
   Using Google I found http://www.redrok.com/electron.htm this is single axis   
   but uses cheap leds as the sensors, this suggest that you can make a 3 by 3   
   or 5 by 5 sensor without breaking the bank.   
      
   Also lots more hits on:   
   http://www.google.ca/search?num=100&q=diy+sun+sensor+tracker   
      
   --   
   I make public email sent to me!  Hydrogen Peroxide Rockets, OpenBeos,   
   SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC.  What happened to   
   the time? http://webhome.idirect.com/~earlcp   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)