Abstract: In this paper we present a concept of an embedded acoustic modem dedicated to underwater communication. The Raspberry Pi is used as a low cost hardware platform. The solution of the physical layer consists in modulation, synchronisation, frames forming, symbol mapping, etc. Specifically, modulation is based upon linear and hyperbolic chirp signal generation. Synchronisation is based upon the correlation of received and transmitted signals. The performance of the communication is tested by computer simulation. This simulation is performed by transmitting signal between two USB sound cards connected by a cable. In the simulation, transmitted signals are intentionally degraded by adding white gaussian noise.