The purpose of this research is to design a Parking Guidance System (PGS) for UBINUS Anggrek Campus' parking building by using Real Time Operating System (RTOS), PIC32, Communication Protocol RS485, and ultrasonic sensor. The system design consists of several main parts, which are Master Controller (PC) as the main system controller, Sensor Controller as the controller for three ultrasonic sensors, and also RS485-to-RS232 Converter as the data communication converter from Sensor Controller to Master Controller (PC), vice versa. The experiments that will be done consists several things, such as measuring and researching UBINUS Anggrek Campus' parking building, measuring the range that can be measured by sensor, determining the safest distance for sensors to avoid interference, and also measuring the time needed for Master Controller (PC) to update data from Sensor Controllers. The result shows that this system can be implemented well in UBINUS Anggrek Campus' parking building without worrying any interference that might occur and sensor can measure well in a distance of 10 - 280 cm. Implementing RTOS into PGS can update data from each Sensor Controller with the average time of 1045 ms from the scale of 133 - 2600 ms. In our system one PIC32 microcontroller can handle up to three ultrasonic sensors reliably because of using RTOS task scheduling
