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 Powermatchâ„¢ 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

System integration is becoming an important issue in the home automation scene. New homes have a number of systems: security, heating, lighting, drapery, audio, video, etc. Each system has its own controller and takes care of its own I/O (Inputs and Outputs). At present, the homeowner needs to learn how each system works and remember the different operational commands to control their electrical environment. This process can be simplified with the integration of a Programmable Logic Controller (PLC).

Most home systems are coming out with an RS232 communication interfaces, which enables two systems to talk to each other. PLC’s have communication ports that can be configured to talk all kinds of protocols. One of the most useful in home systems is the ASCII In/Out non-sequence protocol.

Each home system has their own unique command set of ASCII codes available for monitoring and operating their respective system. The PLC can read and write these codes and translate them to one common user interface, like a touch panel. The touch panel is typically setup as a graphic interface with buttons for each subsystem, thus giving the homeowner one overall control system to operate. The PLC acts on a supervisory level, communicating to all home systems via RS232 connections and passing info to and from touch panels located throughout the home.