Xiaomi Mi Scale 2 BLE Advertisement decode (service 0x181D) and ESPHome config

ble.rs

fn main() {
	vec![
		// real data
		[0xa2, 0x0c, 0x49, 0xe6, 0x07, 0x0b, 0x06, 0x01, 0x16, 0x00], // start
		[0x02, 0x0c, 0x49, 0xe6, 0x07, 0x0b, 0x06, 0x01, 0x20, 0x26], // load
		[0x22, 0x0c, 0x49, 0xe6, 0x07, 0x0b, 0x06, 0x01, 0x20, 0x26], // stable
		[0xa2, 0x0c, 0x49, 0xe6, 0x07, 0x0b, 0x06, 0x01, 0x20, 0x2a], // idle
	]
	.into_iter()
	.map(decode)
	.for_each(|payload| drop(dbg!(payload)));
}

#[derive(Debug)]
#[allow(dead_code)]
struct Data {
	pub flags: u8,
	pub has_weight: bool,
	pub stabilised: bool,
	pub unit: Unit,
	pub weight: f64,
}

#[derive(Debug, Clone, Copy)]
enum Unit {
	Jin,
	Lb,
	Kg,
	Unknown,
}

use std::convert::TryFrom;
fn decode(payload: [u8; 10]) -> Data {
	let flags = payload[0];
	let stabilised = flags & (1 << 5) != 0;
	let has_weight = flags & (1 << 7) == 0;

	let unit = if flags & (1 << 4) != 0 {
		Unit::Jin
	} else if flags & (1 << 2) != 0 {
		Unit::Lb
	} else if flags & (1 << 1) != 0 {
		Unit::Kg
	} else {
		Unit::Unknown
	};

	let weight_raw = u16::from_le_bytes([payload[1], payload[2]]);
	println!("raw={:02x}{:02x} u16={weight_raw}", payload[1], payload[2]);
	let mut weight = f64::try_from(weight_raw).unwrap() / 100_f64;
	if let Unit::Kg = unit {
		weight /= 2.0;
	}

	Data {
		flags,
		has_weight,
		stabilised,
		unit,
		weight,
	}
}

config.yml

sensor:
  - platform: template
    name: "Bathroom Scale"
    id: bathroom_scale
    unit_of_measurement: "kg"

esp32_ble_tracker:
  on_ble_service_data_advertise:
    - mac_address: 70:87:9E:11:22:33
      service_uuid: 181D
      then:
        - lambda: |-
            uint8_t  flags = x[0];
            bool     has_weight = (flags & (1 << 7)) == 0;
            bool     is_stable  = (flags & (1 << 5)) != 0;
            bool     unit_jin   = (flags & (1 << 4)) != 0;
            bool     unit_lb    = (flags & (1 << 2)) != 0;
            bool     unit_kg    = (flags & (1 << 1)) != 0;
            ESP_LOGD("scale", "Flags: %u has_weight=%u is_stable=%u unit: jin=%u lb=%u kg=%u", flags, has_weight, is_stable, unit_jin, unit_lb, unit_kg);

            uint16_t weight = (((uint16_t)x[2]) << 8) + x[1];
            double weight_f = (static_cast<double>(weight) / 100.0) / 2.0; // kg
            ESP_LOGD("scale", "Weight: raw=%x%x u16=%u kg=%f", x[1], x[2], weight, weight_f);

            if (has_weight && is_stable) {
              ESP_LOGI("scale", "Publish weight %f", weight_f);
              id(bathroom_scale).publish_state(weight_f);
            }