使用BLE的Characteristic来传递变量值，并在设备上使用方法来更改它。

例如，在使用Nordic nRF5 SDK for BLE的情况下，可以通过下面的方式来实现：

在蓝牙服务中定义一个Characteristic，用于传递变量值：

#define POWER_CHAR_VALUE_UUID        0x1234
#define POWER_CHAR_HANDLE            0x12

static uint8_t m_power_char_value = 0;

static void ble_power_service_init(void)
{
    uint32_t                err_code;
    ble_uuid_t              ble_uuid;
    ble_uuid128_t           power_base_uuid = POWER_SERVICE_UUID_BASE;

    ble_uuid.type = BLE_UUID_TYPE_BLE;
    ble_uuid.uuid = POWER_SERVICE_UUID;

    err_code = sd_ble_uuid_vs_add(&power_base_uuid, &ble_uuid.type);
    APP_ERROR_CHECK(err_code);

    err_code = sd_ble_gatts_service_add(BLE_GATTS_SRVC_TYPE_PRIMARY, &ble_uuid, &m_power_service_handle);
    APP_ERROR_CHECK(err_code);

    ble_gatts_char_md_t char_md;
    memset(&char_md, 0, sizeof(char_md));
    char_md.char_props.read = 1;
    char_md.char_props.write = 1;

    ble_uuid.type = ble_uuid.type;
    ble_uuid.uuid = POWER_CHAR_VALUE_UUID;

    ble_gatts_attr_md_t attr_md;
    memset(&attr_md, 0, sizeof(attr_md));
    attr_md.vloc = BLE_GATTS_VLOC_STACK;

    ble_gatts_attribute_t attr;
    memset(&attr, 0, sizeof(attr));
    attr.init_len = sizeof(m_power_char_value);
    attr.max_len = sizeof(m_power_char_value);
    attr.p_value = &m_power_char_value;
    attr.p_uuid = &ble_uuid;
    attr.p_attr_md = &attr_md;

    err_code = sd_ble_gatts_characteristic_add(m_power_service_handle, &char_md, &attr, &m_power_char_handles);
    APP_ERROR_CHECK(err_code);
}

然后，在设备的代码中实现一个方法，来更新变量值：

void change_power_value(uint8_t new_value