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Project description

Water Quality Meter

a modern Tri-meter able to accept pH/Ion, eC and temp probes

This project is the combination of years of design, research and innovation in water quality meter construction. Derived from proven designs this unit is a virtual mobile lab in term of water quality sensing. Most water quality meters are designed for a single application or type of ISE or Ion Selective Electrode. This unit was designed from the ground up to interface with many types of ISE, cutting costs and increasing productivity for those that need to take accurate measurements. Weather you need to read pH and eC, or ORP and eC plus temp all at the same time this is your meter, all with the added bonus of being open source hardware!

DIY pH Meter

Inspired by my DIY pH meter build!

The DIY pH meter builds were very effective but had a few shortcomings. Trying to improve on these was always a desire of mine, so I decided to find a better enclosure to build from. The base idea is very sound both from a user standpoint and a design standpoint. the AFE is isolated by default due to the battery driven nature of the device, and the user experience is rather good with proper information displayed on higher quality screens. A larger enclosure meant a bit more room to layout and place the external facing components. It also meant room for a larger screen (in this case for early alpha a 4d systems 2.5 inch tft is used)

Rechargeable and Isolated

Add a LiPo and some battery management and isolate

Since the enclosure has a large cavity it was a no brainier to include a LiPo battery and some charge management ICs, while this makes the build a bit more expensive it has the advantage of knowing SOC of the battery and simply using the LiPo in the first place. Since the unit is battery powered the ISE AFE is naturally isolated. With the addition of the eC unit its a really good idea to isolate one from the other. Simply incorporating the design from the isolation breakout meant a quick and easy way to provide galvanic isolation from the Ion and eC AFEs.


The enclosure is pretty big!

As hinted at above most expensive lab grade meters are tri-meters usually pH eC and temp all in one. Since the enclosure was large enough it made sense to add in the newest MinieC design which makes reading eC a breeze! Generally these are troublesome to have while doing pH or other ISe measurements at the same time, but b providing the isolation barrier mentioned above it allows for simultaneous measurements of ISE, eC and Temp all at the same time.

nice Screen

Display information meaningfully!

One of my main complaints about meters is the lack of information. How much charge is left on the batteries? What state is my ISE probe in? (yes you can tell this with a bit of math from the calibration routines, how much the slope and gain adjustments are off compared to ideal)
Value over time and other various logging and statistics that could be available with updated designs. I am basing the initial alpha off a 4D systems 2.5" TFT, these display are expensive but allow me to offload the screen processing while adding in touch capability which will get the first few prototypes out faster then without. They are nice screen but I really want an OLED in a similar form factor.

Flash for Logging

Shouldn't these units be able to log?

Why not add in data logging. Switch off the screen and let the unit work in low power logging mode to try and capture trends and other anomalies or warning signs. Just like DMMs should have this feature by now so should Water quality meters. The initial design include a 1Mbit flash IC to allow for programming or data.

Over all this project is an attempt to make the DIY water quality meter a more professional unit with expanded capabilities while still remaining fairly competitive.


Expanded version of the DIY pH Meter. This water quality meter combines the strength from the earlier designs with some updated circuitry to allow interfacing with most ISEs.


  • compatibale with pH, ORP, DO, Nitrate and other ISE
  • Battery powered
  • Temp and eC measurements