Telephony Interface Board

This is a picture of the Telephony Interface board. It was originally designed by PC Designs under the direction of Arius Inc. Design checks were done by another consulting engineer, not part of PC Designs. No significant changes were made. Layout was done in PADS PCB under the direction of Arius, Inc. and manufacturing was done in Maryland.

The board includes a Conexant modem, a 4-wire E&M interface, for Types 1 through 5, and steering circuitry for the analog signals. Clearly visible are the two transformers that are used to couple audio to and from the 4-wire interface. To the right of the transformers are the optocouplers that make up the solid state handshake interface, including the E detector. The large black rectangular object on the right is a 24V switching supply used for detector bias. The relay behind the power supply switches the analog subscriber line between channels A and B, when a ring signal is detected on one of the lines.

The small multi-pin connectors on the right (white) are for connecting to two subscriber lines, and to provide the chosen signal to the AIO module. The white connector on the left side of the board is for the 4-wire E&M interface.