This is the result of my investigations into the WLS-MVAxxx battery monitor devices. They have a Bluetooth interface, which is provided by a CH9141K BLE to serial bridge.
So far the result are two python scripts, neither should be seen as "best practice" for writing Bluetooth client or server code.
This is an emulator of the protocol to test host software (and the original Android client) against, written in MicroPython. It should run on a Bluetooth capable controller of your choice, I'm using an Wemos D1 Mini ESP32 – ESP-WROOM board.
Run it in Thonny, and it should print messages to the console. Received messages start with 0xA55A, sent messages start with 0xB55B. It'll appear as a device called "esp32-energy" in the Android WBMS app.
It requires aioble, which can be installed with mpremote.
This is a simple command line client to read data and modify the configuration.
It requires bleak for BLE communication.
python host.py -h
To show usage.
I was wondering about that. Scanning for Bluetooth devices could be used to estimate the user's position, by triangulating against the signal strength and MAC of several devices, or against known devices. So while "normal" apps won't make actual use of this, it is there as a warning.
This is the label on the back of the device, translated with Google translate.
| Description | |
|---|---|
| CN1 | Temperature alerts |
| CN2 | current/voltage alerts |
I didn't see any specification for the temperature sensor, based on measurements with resistors I had at hand I've arrived at 10kOhm at 25 degree celsius and a B0/25 beta value of 3889. NTC 10k thermistors with a beta of 3950 seem to be common on eBay, so I tried one of them. It seems to be close enough - after all I care only if the battery is very cold or very hot, the exact temperature is secondary.
Front view:
| Description | |||
|---|---|---|---|
| J1 | Power + Voltage | Main board | |
| J4 | Current Clamp | Main board | |
| J5 | LCD Back light | Main board | |
| J6/J7 | LCD Zebra Strip | Main board | |
| J9 | BLE Module | Main board | |
| J10 | Temperature Sensor | Main board | |
| J11 | Under voltage + Over Temperature alarm channels | Main board | |
| U1 | MS51FC0AE | 8051 based microcontroller | Main board |
| U2 | TM1622 | LCD driver | Main board |
| U1 | CH9141K | UART to BLE bridge | BLE module |
Back view:
The square chip is the LCD driver.
Front view:
Back view:
The chip is a CH9141K BLE to serial bridge. Only power, RXD and TXD are connected, so advanced features like the "AT" mode are not accesible by the main board.