Some information about the ble protocol of the QP Salt Bright Duo/Pro salt chlorinator, as well as an esphome config to read the data.

The Salt Bright Duo can be configured locally over BLE via a smartphone app called ePool, which also displays some sensor readings like pH, ORP, salt concentration or water temperature. Unfortunately, there is no official way to read these measurements from a web interface or even cloud service for use in e.g. home automation or for logging. The suggested "connectivity addon" turns out to not connect via Bluetooth to the unit, but instead uses its own temperature sensor and can only switch the power to the unit via a relay. Unsatisfied, i decided to do it myself.

To receive data, the device has to be paired/bonded to whatever BLE client one uses. This is done via menu, arrow up/down until "CO(mmunication)" is displayed. Select with OK. Scroll down and select "Bt". Enter pairing mode by selecting "pa". If Bluetooth is turned off, turn it on with "mo".

The device does not simply publish each datapoint on its own characteristic uuid, but publishes everything on a single uuid in packets of bytes containing several datapoints/registers at once.

• Service UUID: 1081
• Characteristic UUID: ef785c24-22bb-463d-b651-0b7445ba091c
• Method: Indications

These packets use an encoding which looks a little bit like ASN.1:
Every packet starts with a nullbyte 0x00, followed by one byte describing the length of the entire packet in bytes. The third Byte seems to be mostly 0x01, in one case being 0x02. The fourth byte identifies the data register being transmitted, followed by one byte denoting the length of the following data. Lastly, the data follows. When multiple registers get sent, the order register, length, data is simply repeated.
For example, lets look at the following Packet: (0x) 00 09 01 0C 01 6D B0 01 36

This is an (incomplete) list of the registers and their apparent purpose:

• Get physical access to the device to see what changing settings (in the app) does to the registers
• Find out how to change settings
• Implement as proper esphome component