Information Technology Reference
In-Depth Information
threshold is set longer, the sound that starts based on the trigger that detects when a
person is entering the bath would be awkwardly late. We therefore determined that
0.8 sec is an appropriate time. The amplitude value is set for a time level of 1.5 s.
The processor will activate an excess amplitude trigger if the amplitude for 0.8 sec
of moving time is above the threshold. However, the trigger only activates during
bathing. This threshold is related to how easily sound plays based on the trigger; so
it can be adjusted by the user.
The breathing component and bathing movement information are processed si-
multaneously. Water pressure data are then converted into water level data by applying
a low-pass filter with a cutoff frequency of 0.35 Hz. The data are subsequently con-
verted again using the bathtub volume and a breathing curve that shows changes in
breathing volume outputted. This breathing curve is then passed to the sound con-
troller. For the heartbeat, the measurement circuit outputs an ECG signal, which is
sent to the computer over the RS-232 C interface. The ECG waveforms are output
directly to the sound processor, which detects R waves and T waves and outputs
height values for each of these waveforms as event signals used for timing control.
When the processor detects R waves, it finds the instantaneous heartbeat from the
interval between the R waves (time interval between the current R and previous R
waves).
6.2.3.2
Sound Controller Module
The sound processor sends the control signal received from the sensing part to the
sound set (Max-patch). The previous sound set sent from the control signal can be
changed as required using the bathtub remote controller and the mixer can adjust the
sound volume before the sound is output to the speaker. The Max-patches (programs)
arrange the data input port that receives control information and the sound data output
port. They have an integrated input/output interface, which makes it is easy to switch
between sound sets.
6.2.4
Sound Design
In our prototype system, we prepared two different sound sets to verify that they
could be switched when it was being used.
6.2.4.1
Sound Set 1
We designed Sound Set 1 to be similar to Soundscape (Schafer
1993
) with an under-
lying sound of gentle waves lapping a tropical seashore in the evening. The lapping
wave sound is mapped so that its volume can be changed using amplitude values.
When the bathwater is stirred strongly, the lapping wave sound increases. Different
