cfsbhawkins / tubby

Hot Tub Water Quality Sensor

Hot Tub Water Quality Sensor

• Battery powered ORP, pH sensor for Hot Tub/SPA
• ~ 1 year battery life @ 2 samples per hour
• Sensor externally mounted, probes placed under the skimmer cover
• Home Assistant Integration
• pH ATC (Automatic Temperature Compensation) integrating with Balboa temperature sensor
• Free Chlorine/Bromine estimate model from PH and ORP values

Hardware

• UM FeatherS2 ESP32 board from here
• 3500 mAh battery or 2500 mAh
• Atlas Scientific Gravity Analog ORP and pH Kits
• Enclosure: DS-AT-0811-S
• 2x100 kΩ resistors for battery monitoring (optional)

Wiring

• Diagram

Firmware

• micropython. OTA & Logging over MQTT
• deep (50µA) & light (7mA) sleep
• Build instructions
• Code

FC (Free Chlorine) ppm Model

Predict Free Chlorine & Bromine ppm from pH and ORP sensors.

• Data source: https://jenfitch.com/free-chlorine-orpmv-vs-ph-new/

Build the model: build_model.py.

Prebuilt models:

• model_fc.h5: model for predicting FC from ORP/pH

• model_orp.h5: model for predicting ORP from FC/PH. This one can be used to calibrate your ORP sensor by getting your water lab tested

Basic script to load and run these models. usage:

python3 ./predict.py  model_fc.h5 666 7.6
-> output:  0.83490694
./predict.py model_orp.h5 7.6 0.85
-> output:  667.04565