Creating a Paging Matrix using the Telephone Hybrid

Will Fraser

Creating a Paging Matrix using the Telephone Hybrid

This design has a number of unique features including:

~ Telephone Hybrid for connecting to POTS or analog PBX
~ DTMF detection for zone selection
~ Tone feedback for operator prompt
~ Design Scalable to 64 + zones

In this design we will discuss creating a Telephone Paging Matrix that can be controlled with any POTS or analog PBX connected to Soundweb London Telephone Hybrid card. The included design is 32 zones but can easily be scaled up to 64 zones as needed.

This design is based around the BLU-800 so that Cobranet can be used to broadcast audio directly to the amplifiers across a network. If your project does not require Cobranet, a BLU-160 or even a BLU-100 with BLU-BOB’s as the analog outputs could be utilized instead.

The audio configuration is very straight forward. There are some standard dynamics processing for tuning the microphone for maximum intelligibility, and a gain point for mute and level control. A delay is used to trap any handset noise at the end of the page.
This feeds a Matrix Router that is controlled via Parameter Presets to route the page to the desired output. A single output Crossover is on each output to provide a gain & mute point as well as some High and Low pass filters commonly required in distributed audio systems.

A 12 band parametric equilizer is provided to allow frequency correction for each output. The multicast Cobranet bundles are used to send the signals directly to the amplifiers across an Ethernet network.

The key to this design is the Hybrid card and the Logic circuit. The circuit needs to accomplish several tasks; automatically answer an incoming call, provide a tones to the caller, detect a two digit DTMF number, route the Telephone Hybrid audio to the appropriate zone, automatically clear the router and reset the logic circuit at the end of the call.
The first action of the circuit is initiated by the Hybrid card going off hook when automatically answering a call. This pulses a Logic End linked to a mute button on the tone generator circuit. This tone provides a prompt for the caller to enter the three digit zone number. This is run through a Logic Not to invert the signal. This also removes the Reset [R] on all the Counter Triggers. This is done through a Logic Link between the Logic End and the Mute button in the Gain object. After the # key is pressed, another tone prompts the operator to begin their page.

At the beginning of the circuit are 11 Logic sources. These are linked to the DTMF detect outputs of the Telephone Input Card by dragging off the Design Tree onto the Logic Source object in the Logic Configuration window. The DTMF Detect values are found under the Telephone Input Card section of the design tree.

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