An underwater navigation system was developed. In contrast to GPS, ultrasonic waves are used in place of electromagnetic waves and buoys are used in place of satellites.

This project refines a foregoing system, which was, however, not working under water. The hardware needed to be adapted for underwater usage and the receiver terminal was redesigned.

A BPSK (Binary Phase Shift Keying) modulated sequence is transmitted by each buoy. The receiver uses the difference of run duration to calculate the distance.

The system was successfully tested in Lake Greifensee as well as in a swimming pool. The two buoys can be used for distances up to 200 m, with a resolution of 33 cm.

Object position data are stored at an interval of one second in the EEPROM and shown on an LDC display. With every start up the data are transmitted to the serial interface.

The system works stable and reliable even at countless echoes.