Hot Tub/Spa & Pool Water Quality Sensor

• Solar powered
• ORP & pH (Optional) Sensors
• Estimates Sanitizer ppm (Optional)
• Home Assistant Integration
• Firmware is using esphome

Log

• Update May 2025: I removed pH probe (3rd broke in 2 years) in December and have been running on just ORP measurements (ORP probe has been much more reliable). Once ORP measurement goes outside the 'green' table range, perform manual pH & alkalinity measurement, balance, then balance ORP with sanitizer. I think pH probe is not worth the cost/hassle in replacement - convenience it adds is marginal, since you still need to measure alkalinity manually.
• Update Dec 2024: Replaced worn-out ORP probe and added SMA Panel adapter. Decreased sampling rate to 1/hour to help battery last when there is little sunshine.

Hardware

• UM FeatherS2 ESP32 board from here
• 2500 mAh
• Atlas Scientific Gravity Analog ORP and pH Kits
• Enclosure: DS-AT-0811-S
• Waterproof SMA Panel Adapter SMA-ADP
• 2x100 kΩ resistors for battery monitoring (optional)

Solar Panel Components

• Adafruit Universal USB / DC / Solar Lithium Ion/Polymer charger - bq24074
• 3.5mm / 1.1mm to 5.5mm / 2.1mm DC Jack Adapter
• Small 6V 1W Solar Panel
• JST-PH 2-pin Jumper Cable

Wiring

• Diagram
• NOTE: You can skip the ambient sensor removal step

Firmware

• Install Python (Tested 3.13.3)
• Open Command Prompt
• pip install esphome==2024.12.4
• copy wifi_example.yaml to wifi.yaml and edit the new file
• Connect the board via USB and enter esphome run tubby.yaml on the command line. This will build and upload firmware to the board.
• In Home Assistant, create a helper switch input_boolean.ota. Enable this switch, it will prevent device Deep sleep.
• Power cycle the board, Device then enters Light sleep for 15 minutes before it shows up in Home Assistant
• Once your esphome device is added to Home Assistant, Use Device's page, Diagnostics section to calibrate the probes:
  • ORP Cal : mV ORP calibration offset from raw ADC value. Note: ORP mV Sensor value has calibration applied
  • pH 10 Cal: mV reading from pH Raw sensor while submerged in pH 10 calibration solution
  • pH 7 Cal: mV reading from pH Raw sensor while submerged in pH 7 calibration solution
  • pH 4 Cal: mV reading from pH Raw sensor while submerged in pH 4 calibration solution
  • ppm Factor: 1 - Chlorine, 3 - Bromine
• Turn off input_boolean.ota to allow the device to save some power.
• Place the probes in the water, and enjoy!

Sanitizer ppm Model

• pH + ORP -> Chlorine ppm Conversion Table
• Machine Learning Notebook
• Generate .h file from .tflite: xxd -i model_fc.tflite > model_fc.h