This pcb is a breakout board for the KS0835F SLIC (subscriber line interface) module.

The SLIC module emulates a plain old telephone service (land line central office).

A telephone or modem etc can be connected to this module, which acts as a phone service land line provider.

This can be used to test telephone devices or create a local intercom or telephone network, etc.

It has pins to connect a telephone/device tip and ring, and provides approximately 48 VDC for phone on hook voltage.

A control input can be toggled at a certain frequency to generate over 70 VDC (alternating polarity) on the tip and ring to generate a ring signal.

An output pin indicates whether a phone is on or off hook.

When off hook, there are dedicated pins for an audio input and output connection, allowing audio interfacing with the phone line.