[continued from previous message]   
      
   space - it's looking over the fence into adjacent areas. There's   
   absolutely nothing wrong with that but it doesn't get you all that far.   
      
   > What's fun is to brainstorm a project that's well along, and maybe   
   > reboot the design. Sunk cost thinking is the enemy there.   
      
   Continuing to spend money on a approach that doesn't look too promising   
   isn't a great idea.   
      
   > Parts obsolescence isn't all bad.   
      
   I had great fun with that once - the Metals Research/ Cambridge   
   Instruments GaAs single crystal puller relied on an LVDT and spring to   
   very precisely track the weight of the crystal being grown.   
      
   The dual emitter transistor used in  the oscillator that energised the   
   LVDT went obsolete and I ended up inventing a current mirror version   
   version of the Baxandall class-D oscillator to generate a really clean   
   and stable sine wave to drive the LVDT. Putting in an LT1028 to amplify   
   the output of the LVDT  meant that I could use less excitation current   
   in the LVDT, and it stopped drifting on start-up.   
      
   Getting rid of the uA741 that amplified the DC output from the   
   demodulator, and replacing with an op amp that did have a 1/f noise spec   
   was the only change the operators noticed - the RF heaters that kept the   
   GaAs molten started running at a steady 30% rather than banging full on   
   for 30 seconds and going right off for the next minute or so.   
      
   It took more than a day to pull a crystal, and the operators found the   
   process much more restful after the up-grade.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)