Conductivity sensor

electrical conductivity... varies quite a lot. Hard to compare old values without looking at a probe in till as we didn't calibrate much before

• Jeff's new one? amp and oscillator
  • nice and small
  • will have code etc to reuse from tijuana node
• SEMEC chip?
  • quite large - hard to get?

non rusting bolts/terminals needed in probe - perhaps smaller or closer together?

M5 bolts similar to those used before (how small can we go?) need to stick out