can not be done easily on different places and different beds.
We, probably, need separate power supplies for each circuit in
a different environment.
Packet loss. Using wireless communication to transmit signal
can lead to packet losses due to interference in the environment.
For example, in our system, we observe an average
packet loss rate of 10%. To address this challenge, we take
into consideration the fact that we have multiple load cells
in the system and there is sufficient redundancy in the data.
Therefore, we use interpolation techniques to overcome the
missing data problem, which will be explained in detail in
Section IV. Moreover, we strive to minimize the packet losses
through careful placement of the system, especially the base
station.
III. MOTIONSCALE HARDWARE DESIGN
Our MotionScale system consists of four major components:
a load cell circuit, a differential amplifier circuit, a power
switch circuit, and a wireless communication component. The
load cell measures the voltage change due to motion. Because
the raw voltage change values are usually very small, it is hard
to accurately measure them directly. In order to capture such
small changes in voltage, we design a differential amplifier
circuit to amplify the raw voltage measurements for subsequent
processing. In order to reduce its power consumption,
our system exploits a power switch circuit that can switch
the load cell and amplifier on or off, depending on a control
signal from the communication component. In addition, we
leverage a RF Transmitter (referred to as PIP-Tag, designed in
our group [11]) that converts analog voltage signals to digital
values, and sends the digital values to the basestation Unit
through low-energy wireless communications. The basestation
is connected to a laptop through a USB port, from which we
receive data for subsequent processing.