Earth current modem for communication through rock and earth with user interface to write and read messages and for system configuration. Also contains a rechargeable battery.
The first version of the Cave-Link systems consisted out of an earth current modem and a Palm device as user interface. Under cave conditions the Palm proved a failure, therefore user interface and modem was combined in one package.
The earth current modem can transmit and receive data thru several hundred meters of rock or earth.