Establishing a VoIP Public Address System

Overview

Instant PA is an add-on for Astribank™ that interfaces with any Astribank FXS port to provide public address functionality via Astribank. The small stand-alone unit is activated by simply dialing the port’s extension number.
Each Instant PA unit is equipped with 2 RJ11 ports. The ‘PBX’ port connects directly to an Astribank FXS port and the ‘PA’ connection connects to the PA ‘line in’ (‘audio in’) port. The PA device itself can be anything from a standard personal computer speaker with an internal amplifier to an industrial-strength amplifying system.

Figure 1: Instant PA connected to Astribank and loudspeaker with internal amplifier

For a description of the connection pins setup see Table 1, below

How it Works

Instant PA does not need a power supply - it uses the Astribank FXS feed for its operation. A LED (Light Emitting Diode) indicates "line active" status, simplifying installation and testing.When a call is placed to the FXS port extension to which the Instant PA is connected, the Instant PA immediately "answers the call" (i.e., goes to "off hook" position) and the caller can place his/her call through the IP system. The origin of the PA message in not important; it can be an analog phone, an IP phone, a call from an incoming line or even from a soft phone overseas. The PA system is automatically disconnected when the call terminates.

The small size and simple installation of the Instant PA unit makes it easy to install multiple

The small size and simple installation of the Instant PA unit makes it easy to install multiple local PA amplifiers in different locations. Even a low cost PX loudspeaker (with built-in amplifier) can be used as a small PA system.

Multiple Instant PA devices can be connected to multiple FXS ports and loudspeakers to provide multi-zone support.

Implementing the Instant PA

Each FXS line connected to the Instant PA must be defined as Kewl Start, as per Astribank's default setting. If for any reason the setup is different, see the "Kewl Start Setup Procedure" below for proper settings. This is important in order to enable automatic disconnection from the PA system when the call terminates.

Note: Instant PA should be located close to the PA amplifiers.

Table 1: Wiring Table

Kewl Start Setup Procedure

In the /etc/zaptel.conf file the channel must be defined as "fxoks". For example:

fxoks=1

In the /etc/asterisk/zapata.conf file the channel must be defined as fxo_ks.

For example:

signalling=fxo_ls

For more information about this application and or Xorcom products in general, please contact us.