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Reply To: Inexpensive DIY conductivity sensor

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Hi Neil,

We are looking at developing a network of Mayfly stations for characterizing a catchment, with three tiers of sensor quality.  The top tier (~10% of stations) would have top-standard sensors, and would be used to calculate loads at the bottom of the catchment, or investigate interesting signatures at certain sites.  The middle tier (30%) will use cheaper, but reliable sensors, e.g. Decagon CTD, Yosemitech Turbidity etc.  The bottom rung (60%) will be DIY quality, i.e. cheap but reliable, and is aimed at increasing resolution throughout the catchment.  This work would fall into the latter.

We were thinking about using washing machine turbidity sensors for the DIY tier, but these don’t seem to be reliable for field applications (based on our lab experiments).  I have had some success building my own turbidity sensor using a piece of PVC pipe, a smaller acrylic pipe with a red LED, 180 and 90 degree LDRs.  This worked really well in the lab, but seems to pick up daylight in the field.  I found an interesting paper (https://ieeexplore.ieee.org/document/8337739/) that uses the same design, but with photo diodes and an infrared LED light source.  They were planning to deploy in the field, but I imagine they will come across the same problem.  I think there is potential down this pathway, but haven’t found an ideal solution yet.

I would like to add a DIY conductivity sensor to go along with the DIY turbidity sensor, and possibly other DIY sensors (e.g. depth, UV absorbance etc).  The overall aim is to build relationships with contaminants (e.g. TN, NNN, DRP, TP, ECOLI, TSS..) over storm events, and better understand spatial and temporal load contributions to sensitive receiving environments.

Ideally we would telemeter data to MMW, but we are having a few issues with the XBee LTE.  It’s not a complete disaster is we have to manually download the Mayfly, but better for community communication if it’s live on the web.

This work is through the University of Waikato in New Zealand, so there are some very experienced technicians who can help with the build.  We also have a 3D printer, which may make things easier.

I am just beginning this journey so I will probably ask a few silly questions along the way 🙂