IEEE Consumer Electronics Magazine - September/October 2022 - 97

The last 8 bits are currently not used. The duration
of the dive is calculated on the other
WADAC from the depth received. The modem
M64 consumes an average of around 2.6 W and
was attached outside the watertight enclosure
and connected to the inside by cable penetrators.
The watertight enclosure is made of cast
acrylic plastic with an inner diameter of 50 mm
and a length of 150 mm with a depth rating of
250 m. Each side of the enclosure is sealed with
a flange cap made of aluminum and two holes
which house the connections to the outside.
Communication with the microcontroller was
implemented using the 3.3 V UART. Since the voltage
for the modem must be somewhere between
10 and 18 V, a 3S lithium polymer accumulator
(LiPo) with 1000 mAh was chosen as the energy
source. This ensures continuous operation for
about 3-4 hs. Since the microcontroller allows a
maximum of 6 V at the input, a Stepdown Tracopower
tsr 1-2450 was switched between the LiPo
and the Teensy. A digital current sense amplifier
from TE the INA219 transmits permanently the
power consumption from the modem and the
other components via I2C to the microcontroller.
This information is then shown to the user next
to the date on the 1.800 full 18-bit color display
with a resolution of 128 160. To demonstrate
the capabilities of the WADAC, a heart rate
receiver released by Polar was added, which
records any signal at a frequency of 5.2 KHz.16
This is a commercially available and widely used
uncoded chest strap sensor that is primarily
used in the fitness sector. The calculation of the
current heart rate is added and averaged from
the last ten registered signals based on the time.
The Polar T34 chest strap used for this allows a
maximum water depth of 100 m. An expansion or
replacement of the system with the SPo2 measuring
device developed by ONIN OEM III is also possible
and has already provided acceptable
results in another study.10
AIM and Approach
The aim was to develop a dive computer that
has all the basic functions is easily expandable
and enables communication between several of
the same type. The focus was on lakes with poor
visibility of only a few meters as well as great diving
depths in the sea. In both situations, it can
take a few seconds to several minutes before the
September/October 2022
safety diver knows about the condition of the
freediver. In a threatening situation for the freediver,
these periods of time can significantly
reduce the reaction time of the safety diver,
whereby accidents and their consequences can
be minimized. A not insignificant question that
arises is how a freediver reacts to such a technical
development. Is the freediver more likely
looking for inner peace combined with relaxation
and does not want to be distracted by such
a dive computer or would the freediver like to
know where their diving partner is at any time.
Dive Experiment
In order to find out the general product acceptance,
the developed WADAC was made available
for a full day during a freediving event in Ibbenb€uren
and another day in the Aggertalsperre then
evaluated using the UEQ.17 Fourteen people were
enrolled for this study which were all healthy freedivers
(12 men, 2 women) with an average age of
around 50 (M ¼ 53.5, standard deviation [SD] ¼
11.38), between 29 and 65 years old.
To assess the experience of the freedivers as
best as possible, the number of dives deeper
than 20 m were used as an indicator, in which the
average was 350 dives (M ¼ 200, SD ¼ 333) ranging
between less then 100 and more than 1000
dives. The personal best (PB) in deep diving with
an average of around 34m(M¼ 33, SD¼ 9.2).
Informed written consent was obtained from
each participant as well as subject information
about possible risks and challenges.
The tests took place in the Aggertalsperre
(Figure 3) and during a freediving event in
Ibbenb€uren where all necessary safety regulations
where met as well as a medical statement
about the fitness to dive and a brevet from any
of the recognized diving organizations.
During the event, each individual participant
could choose whether he wanted to participate
in the survey. During the dives, the WADAC was
either attached to the arm like a wearable or
held in the hand. Each of the participants could
choose the duration and number of dives. Dives
into caves, wrecks, and other underwater facilities
were carried out at will, where there was
most of the time no visual contact between the
participants. Thanks to the use of an independent
safety diver, it was still possible to secure
protection for those who were diving at any
97
IEEE Consumer Electronics Magazine - September/October 2022

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