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BUILD A VIRTUAL WIRELESS AUTOMATION SYSTEM

by Michael Chan

Start ý X-10 ý The Scheme ý The Interface ý The Construction ý Sources and PDF

In this cyber age, everyone knows what virtual reality means. All those computer animations and electronic games appear so alive that they give the illusion of reality. The concept of virtual wireless control in this article is similar.

The ease of control commands (a few keystrokes on the telephone keypad) and the absence of physical wiring installations renders this project scheme virtually wireless. It feels like wireless. But in reality, it isnýt. I simply exploited the existing wiring systems that are already installed in-house (namely the telephone network and the AC lines) in our working plan. In essence, the control signals are sent as DTMF codes through the telephone line, they are decoded by the Telecontroller and interpreted by the computer, which then broadcasts X-10 commands over the AC lines to operate corresponding appliances via the CM11A interface.

Before I go into the details of the scheme, a review of the fundamentals in DTMF and X-10 signals is in order.

DTMF DECODER

Modern telephone equipment employs unique electronic tone pairs, which are now standard in the field of telecommunications, to represent telephone dialing numbers in a system known as Dual Tone Multi-Frequency (DTMF). There are many IC chips on the market that capture DTMF signals and convert them into binary codes.

Mitelýs MT8870 DTMF decoder chip that is used in the Telecontroller is a complete DTMF receiver that accepts DTMF tone pairs and digitizes them into 4-bit codes. The chip works seamlessly with the computer. It validates incoming DTMF signals and passes them in bits to the computer via the parallel input port. A cross-reference table of DTMF dialing and 4-bit codes is given in Table 1.

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