SX On-hold messaging switch

SX On-Hold Messaging Switch

Abstract

Most modern PBX systems have what is called an external audio port. This port is usually used to playback promotional marketing or music recordings to callers while they are on hold. These devices are usually called on-hold messaging devices. Sometimes the commercially available products are not always flexible enough to work in every situation.Under normal operation of the message on hold feature, all callers when placed on hold will hear the same recording regardless of which external line they are on.

The SX On-hold Messaging switch device adds a level of flexibility to any company that has a PBX and wants to add Message or music on hold features, they would be able to play different music or messages depending on which external telephone line a call is on; For example suppose in a particular company you have four departments using the same PBX system but with each having it's own set of outside lines. By using this device you can actually play music for one department's customers when they are placed on hold, promotional recordings for another department's customers, recordings of recent company news for another and company trading information for another.

SX On-Hold Messaging Switch Device Operation

A 2Khz audio tone is placed on the external audio port of the PBX system, and the telephone lines that are connected into the PBX are monitored for this tone.
Whenever a call is placed on hold, the PBX system connects whatever audio information is on the external audio port on the line, which in our case a 2Khz tone, to telephone line. When the microcontroller detects this tone, it activates two relays. The first relay seizes the external line and connects the on-hold device, while the second relay disconnects the line from the PBX, therefore the external party will not hear the tone while the on hold device is playing on the line. The external party then hears the Message on-hold information. When the party on the PBX side picks back up the call the PBX systems removes the tone that is on the external audio port from the line. The microcontroller detects the removal of the tone, and deactivates the two relays in reverse order, first it connects the telephone line back to the PBX then it removes the seizure circuit and the on-hold messaging device.

Line interface schematic
CPU schematic
Source Code
Future Plans

Troy Duncan
Cable and Wireless Jamaica.
tduncan2@hotmail.com

Questions: