Home audio systems are becoming more and more important to new homeowners. They have AM/FM receivers, CD players, satellite/cable, and even the Internet as sound sources located usually in the media room. Stereo sound is piped into almost every room in the house via in-wall or ceiling speakers. What is also required is volume control in every room, which means additional keypads on the walls. These additional keypads add to the switch wall clutter, but when the volume control is incorporated with the programmable logic controller (PLC), this switch wall clutter is eliminated.

The best way to control volume is to use digital volume control. Digital volume control attenuates stereo speaker signals in multiple steps. On the top step it directly connects the speaker to the amplifier. Some digital volume controllers include Powermatch™ circuitry allowing up to eight controllers to be connected to one receiver. Rather than use specialized audio keypads to control room sound levels, scene lighting keypads already connected to the PLC will incorporate the volume up, volume down and mute functions. This is accomplished with an external audio interface.

The audio interface (VCI 28) uses a two input serial signal to control volume up, volume down and mute individually on each of the digital volume controllers. The PLC delivers a signal pulse train on two of its relay outputs to the audio interface. The output pulses are set at 100msec intervals.

The PLC allows the homeowner to control not only the lighting and drapery systems, but also the audio volume levels in every room from one single keypad.

For information on the digital volume control interface; http://www.knollsystems.com/vci28.htm