Review on Arduino-Compatible TDS Meter Probe for Water Quality Monitoring V1 Sensor Module with XH2.54-3Pin Jumper Wire Connector by KEYESTUDIO by Mark Green

I bought two of these to measure the TDS of the water entering my reverse osmosis system and the levels leaving it. That way I know when to change the filters instead of blindly doing it every x months. The data is saved in the Home Assistant and I get a push notification if I need to replace it now. First, I connected these sensors to an analog-to-digital converter (ADC) on an ESP32 microcontroller and tested it in both the Arduino IDE and ESPHome. . Tension was everywhere, generating garage readings. Instead, I used an ADS1115 (16-bit, 4-channel ADC) and connected it to the ESP32 via an I2C interface. This fixed most of the repeatability issues and I finally got stable readings. HOWEVER, there were still many differences in readings from one probe to another. I had to calibrate each sensor individually to fix this. There is an Arduino example of this product online that includes the calibration formula - ignore it, it's completely useless. Instead, I made eight different concentrations of calibration solution by mixing lab-grade deionized water and table salt. I then plotted the observed voltage at each concentration and obtained a linear calibration curve using the least squares method. (Sounds complicated, but it's pretty easy to set up with the "Calibrate_linear" filter in ESPHome). I did this for each of the two sensors and created a unique calibration profile for each. Now everything works and pretty much meets my needs. I'm a bit concerned about the long-term drift, but over time I'll update this review with my experiences.