**3. Proposed Wrist-Mounted Dive Computer for Underwater Drawing and Writing First Bullet**

The proposed DiverPAD are composed of applications processor (AP), battery charger, power management, display, sensors, and Bluetooth based connectivity modules as depicted in Figure 4. While DiverPAD can provide the functions of conventional dive computers, its main feature enables to provide the function of underwater drawing. Therefore, DiverPAD was newly modified on four major modules for supporting the underwater drawing, which are firmware, protocol, user interface, and underwater touch screen.

**Figure 4.** Block diagram of DiverPAD.

In addition, we set DiverPAD's target values in terms of supply voltage, operating time, operating temperature range, waterproof depth, charging time, and battery capacity to ensure drawing capabilities as well as existing conventional functions as described in Table 1.



### *3.1. Firmware*

There are three main operations in terms of firmware in DiverPAD as followings: First, it prescribes the specific module code that makes up the hardware. Second, it controls the user interface (UI) for terminal device operation. Lastly, it stores user data (sensor, text, and image data).

As depicted in Figure 5, DiverPAD's firmware is installed into the main controller and it is combined with power status information, sensor detection, screen configuration, mobile linkage, and environment setting to maintain function-based calling relationship. After the initializations of each module is performed, DiverPAD operates specific functions like drawing according to "DiverPADTask" as presented in Algorithm 1, which is obtained from the touch panel by pressing the touch pen. As the insulator came into the reservoir space, upper and lower layers contact. Following this, the touch panel unit recognizes the point of contact and performs the drawing and writing process. When the user releases the touch, the restoring force raises the upper layer, as a result the insulator flows back from the reservoir space to the touch space and returns to its original state.


**Figure 5.** Firmware design of the proposed DiverPAD.

In addition, DiverPAD has eight supplementary LEDs as a means of emergency indications which are a real-time clock for dive time, a booster circuit, a switch module for various menu operations, a boot loader for firmware update, and a watchdog timer to prevent malfunction. Depending on the level of training of underwater activities, when the depth and time limit of each individual is exceeded, the LED module provides a notification function to the diver as presented in Algorithm 2. After the LED module was implemented in the form of firmware, we conducted the field tests of LED recognitions in both restricted and open waters. It can be seen that the LED brightness is high within 10 meters as shown in Figure 6.

### **Algorithm 2** dive qualification method

```
Input: positive integer User, integer depth, positive integer count
positive integer clock, char cert
Output: LED alarm 1: if (count < 5) then
2: DiverRight <- beginner.
3: if (depth > 18 m) then
4: LED = Warning (RED).
5: Else
6: LED = Warning (Green)
7: Else
8: if count is positive, then DiverRight = Openwater; Advenced; Rescue; Master;
9: Return DiverRight.
10:
11: switch (clock)
12: case (9 < clock < 18)
13: LED = Warning (Green)
14: if (clock > 18)
15: if (user = cert)
16: LED = Warning (Green)
17: Else
18: LED = Warning (RED)
19: Return LED alarm.
```


**Figure 6.** Field tests of LED recognition.
