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Screen freeze (or no response) is a condition that often occurs in a Personal Computer (PC). In this condition, the PC has lost the ability to respond to its application programs. The same thing can also happen to a data logger, which is usually constructed by using a microcontroller or embedded processor. We propose a design of a dual microcontroller to overcome hang, or no response, of the main microcontroller in a data logger. One of the smart features is an auto restart or reboot, so the data logger with the 'no response' condition is able to reboot without operator assistance. We used an ATmega128 as the main or master microcontroller and an ATtiny13 as the watchdog or slave microcontroller. The watchdog microcontroller detects the activity of the main microcontroller by monitoring a periodic signal from the main microcontroller. If a disruption occurs in the system and the main microcontroller is not able to send this periodic signal, the watchdog microcontroller would determine that a system failure has occurred. System failure will trigger the watchdog microcontroller to activate a relay to reset the main microcontroller. This capability is expected to increase the stability of the data logger and minimize the measurement data lost.

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Ozonizer is a method used for sterilization and food preservation by utilizing ozone produced from plasma discharge. The effective way of obtaining ozone is to use dielectric barrier discharge (DBD) plasma. The manufacture of a controlled ozonizer chamber system is important to result in effective and efficient performance. The aim of this study is to design and optimize the ozone chamber parameter using pulse width modulation (PWM). The system design is added with the Arduino Mega 2560 microcontroller and the L296N motor driver as an ozone generator radiation controller by changing the pulse width modulation to determine the ozone levels produced. The experimental results show that the ozone concentration increases by 50 % on average with increasing variations of the 10 % duty cycle (PWM) and the ignition time length. The optimum value is achieved on a 70 % duty cycle for 60 - 300 seconds, where the ozone level of 3 ppm is obtained and sustained for fruits/vegetables sterilization and preservation application.

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