many thanks for the pointers and for @aufdenkampe system level parts.
I haven’t used the Mayfly before though I got Mayfly 0.4 and chatted with Shannon when she was in San Francisco.
I’m building a test capability for interfacing to Keller Nanolevel depth sensor – RS485/Wingboard/Mayfly 0.5b.
If I can juggle it, and pull together a remote monitoring of low water levels in streams using the Nanolevel I hope to share it at the 2019 Apr23rd https://www.calsalmon.org/conferences/37th-annual-salmonid-restoration-conference. It turns out low stream flow monitoring in the last 25mm of water, with diurnal temperature fluctuations and remote stream valleys, is challenging.
again thanks for the pointers, just put out a Digikey order.