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BUILD A VIRTUAL WIRELESS AUTOMATION SYSTEM

by Michael Chan

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

THE SCHEME

The overall home "wireless" automation project is illustrated in Photo 1. The Telecontroller, together with the CM11A interface, works neatly alongside the computer. The former enables the PC to talk to the phone line via the parallel port and the latter helps the computer communicate with the X-10 controlled devices through the serial port. After the Telecontroller answers the phone and validates the security codes in the form of DTMF signals, the PC instructs the CM11A interface to talk to the corresponding controlled devices.

Photo 1ıThis is the overall working scheme for the project.

Hereıs the scenario. Before I leave my office to head home, I want turn on my air conditioner to cool down the house to a comfortable level in the summer. When I get around my street corner, Iıd like to open the garage door, turn the porch light on if itıs dark, and disarm my home security. These could all be achieved with a few keystrokes on my mobile phone!

The beauty of the present scheme using X-10 modules is its high degree of expandability and flexibility. Any changes in the system configuration involve only minor software modifications. Practically no physical installations are necessary because the X-10 modules use existing AC lines in communication.

THE TELECONTROLLER CIRCUIT

The Telecontroller is a telephone interface to the PC. It interprets ringing and DTMF signals in the phone line and digitizes them into binary levels for the PC to read. The Telecontroller circuit shown in Figure 1 can be divided into three major partsıthe phone interface, the printer port connection, and the decoder circuit.

Figure 1ıHere you can see the Telecontroller circuit which is divided into three partsıthe phone interface, the printer port connection, and the decoder circuit. click here to enlarge

The phone interface is responsible for reporting incoming rings to the PC. Any ringing signals across the phone line will be rectified through diode D1 to operate the optocoupler (IC1). As a result, pin 4 of the IC1 will be pulled up high (5 V). The ratings and values of coupling C1, C2, and filtering C3 capacitors are critical. Values that are too high could result in damaging high currents, and values that are too low could make operation erratic. Upon verification, the PC answers the phone by connecting the loading resistor (R13) and the detector circuit across the phone lines with relay 1.

Transformer T1 is used to isolate the decoder circuit from the phone line. After the decoder chip detects a valid DTMF tone, its steering output (pin 16) will present a logic high and prompt the PC to read the latched 3-bit code from the decoder data register. (Owing to the limited number of input bits (only five), I could only tap three bits for the code detection while the other two input bits are for ringing and valid DTMF validation.)

Communication between the PC and the Telecontroller is done through the printer port connections. Two of the five input lines (10 and 11) are used for detecting the presence of ring and DTMF tones, respectively, and the remaining three (12, 13, and 32) are used to read DTMF codes. One of the output lines of the printer port (3) is used to answer the phone by turning on relay 1. Relay 2 in the controller circuit is an optional feature for single-device standalone control applications. The 5-V power supply for the detector circuit is regulated by the action of IC3 on a 9-V battery.

A parts list for the Telecontroller is available.

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