Read data from a LIONTRON battery

liontron.js

// This is a POC that reads data from a Jiabaida BMS, as it is integrated 
// in the Liontron battery that I have.
// It's basically the same information as it is displayed in the buggy app that
// comes with it.

const {createBluetooth} = require('node-ble')
const {bluetooth, destroy} = createBluetooth()

// BLE adress of the battery - this will be different from battery to battery
const DEVICE_ADRESS = "A4:C1:38:C5:96:C9";

// These UUIDs stay the same, they are hard-coded into the app
const SERVICE = "0000ff00-0000-1000-8000-00805f9b34fb";
const CHARACTERISTIC = "0000ff01-0000-1000-8000-00805f9b34fb";
const RW_CHARACTERISTIC = "0000ff02-0000-1000-8000-00805f9b34fb";

async function main() {
	const { bluetooth, destroy } = createBluetooth()

	const adapter = await bluetooth.defaultAdapter()
	const device = await adapter.waitDevice(DEVICE_ADRESS)

	console.log("found device", await device.getAddress(), await device.getName());

	await device.connect();
	console.log("connected");

	const gattServer = await device.gatt()
	const service = await gattServer.getPrimaryService(SERVICE);
	const readCharacteristic = await service.getCharacteristic(CHARACTERISTIC);
	const writeCharacteristic = await service.getCharacteristic(RW_CHARACTERISTIC);

	await readCharacteristic.startNotifications()

	readCharacteristic.on('valuechanged', buffer => {
		if (buffer.length < 7)
			return;

		if (buffer[0] === 0xdd && buffer[1] === 0x03)
			decodeBaseInfo(buffer);
	});

	// Periodically query data
	setInterval(() => {
		// dispatch a BMSBaseInfoCMDEntity 
		const buffer = Buffer.from([0xdd, 0xa5, 0x03, 0x00, 0xff, 0xfd, 0x77]);
		rwChar.writeValue(buffer);
	}, 1000);
}

function decodeBaseInfo(buffer) {
	console.log("total voltage: " + shortToFloat(buffer[4], buffer[5], 100) + "V");
	console.log("current: " + shortToFloat(buffer[6], buffer[7], 100) + "A");
	console.log("remainingPower: " + shortToFloat(buffer[8], buffer[9], 100) + "Ah");
	console.log("nominalPower: " + shortToFloat(buffer[10], buffer[11], 100) + "Ah");
	console.log("cycles: " + shortToFloat(buffer[12], buffer[13], 1));
}

function shortToFloat(high, low, scale) {
	const value = ((high & 255) << 8) + (low & 255);
	const sign = (high >> 7) === 0 ? 1 : -1;

	if ((high >> 7) === 0)
		return value / scale;

	return (value - 0x10000) / scale;
}

main().then(console.log).catch(() => {
	device.disconnect();
});