*- 100k --*
            |         |
--*-- 100k -*-|      |
  |           |      |
  2           |      |
  5           |      |
  0           |   /---*-- out to adc
  R           |  /
  |           | /
--*-- 100k -*-|/
            |
            |
            *--  100k --> bias pot, adj for 0 V out @ 4mA
            |
            1
            0
            0
            k
            |
           Gnd