+5V --+--------+
             |        |
             |        X
             X        X 10K
             X        X
             X        |
             |        +---------- CS1
             |      |/ 
             +------|  NPN
             |      |\  
            ---       V
   Vz=4.7V  / \       |
            ---       |
             |        |
             |        |
           -----    -----
            ---      ---
             -        -