Smart-Badge: A wearable badge with multi-modal sensorsUbiComp/ISWC ’22 Adjunct, September 11–15, 2022, Cambridge, United Kingdom
privacy well protected is becomming more and more popular [
25
]. Luo et al. [
16
] demonstrated a minimal and
non-intrusive, low-power, low-cost radar-based sensing network system recognizing 15 kinds of activities with
an accuracy of 92.8 %. However, this solution lacks exibility as the sensing network system should be deployed
in the kitchen and can only detect the activity in a limited space. The wearable device has shown more exible
advantages over such distributed sensor system. Yasser et al. [
19
] presented a dataset for 15 kinds of kitchen
activity recognition using smartwatch accelerometers. Besides, they achieved a classication precise of 97.6
% with the use of CNN based approach, which shows that a weareable device has a great potential in kitchen
activity recognition.
2.2 Multi-modal sensors platform in human activity recognition
Compared to the limitation of computer vision technology in the human activity recognition area, like space-time
limitations, easy invasion of user privacy, and high energy consumption, the sensor-based methods with many
advantages like compact, low cost, and high computational power have become the focus of attention [
23
]. A
single special-purpose sensor can only recognize single series activities. It also suers from low robustness in
most cases because most sensors have limitations due to sensor deprivation, limited spatial coverage, occlusion,
imprecision, and uncertainty [
9
]. Besides, an unhealthy lifestyle is usually the result of much bad behavior. Thus,
using a single sensor for human activity recognition is not a perfect option in many scenarios. The concurrent use
of multiple sensors for human activity recognition provides a practical solution for complex activity recognition,
and improvement of recognition accuracy [
1
]. For example, Zhang et al. [
30
] designed a necklace with multiple
embedded sensors, such as a proximity sensor, an ambient light sensor, and an inertial measurement Unit (IMU)
sensor. The necklace can detect the eating activity more accurately after augmenting the proximity sensor data
with the ambient light and IMU sensor data. Bharti et al. [
4
] proposed a HuMAnsystem with ve kinds of sensors
such as IMU, temperature, air pressure, and humidity sensor, as well as Bluetooth beacon, which are deployed
on dierent parts of the body. This system showed that 21 complex activities at home could be detected with
high accuracy. Gravina et al. [
10
] demonstrated a system based on body-worn inertial sensors combined with
a pressure sensor to monitor in-seat activities, by which four ordinary basic emotion-relevant activities were
recognized with high accuracy. These studies about human activity recognition shows that complex human
activity can benet from multi-modal sensors information, which can increase system reliability and improve
recognition accuracy. In this paper, we design a wearable smart badge base on multiple modal sensor platform
with six dierent sensors to recognize kitchen activities, which could help users know and understand their
habits.
3 HARDWARE IMPLEMENTATION
The ergonomics and ease of use are of paramount importance for a wearable device, which can not be a burden
to the user during wearing [
6
]. Therefore, a smart light wearable badge was designed in this work, which can be
attached to many parts of the body exibly and easily, like shoulders, hips, and chest. As shown in Fig. 1, the
smart badge hardware system consists of four main components such as sensor module, microcontroller module,
data logger module as well as data transmission module. Six dierent sensors (IMU, optical sensor, gas sensor, air
pressure sensor, thermal IR array, and Time of Flight (ToF) ranging sensor) are connected to two microcontrollers
via the I2C interface. 791 channel data from these six sensors, including body motion and ambient information,
are sampled. Since the sample rate of these sensors varies considerably, for instance, the sample rate of IMU sensor
LSM9D01 is up to 400 Hz in fast mode, while the sample rate of gas sensor CCS811 is only 4 Hz. If all sensors are
connected to one I2C bus system, the sampling rate will be decreased dramatically. Furthermore, the number
of communication interfaces of one micro-controller is limited for connecting the six sensors separately. Two
microcontrollers (NXP iMXRT1062 based on high-performance ARM Cortex-M7 processor core and nRF52840
3