Garra Crema

AN236
X-10® Home Automation Using the PIC16F877A
Author: Jon Burroughs Microchip Technology Inc.

HARDWARE OVERVIEW
The home controller application described in this application note allows the user to program on and off times for up to sixteen devices, using a 2 x 16 liquid crystal display and five push buttons. A built-in light sensor can be used to turn on lights at dusk, and turn themoff at dawn. The home controller is designed to facilitate experimentation with home automation using the PIC16F877A. In addition to the PIC16F877A, the board will accept any other PICmicro MCU that shares the same pinout, such as the PIC18F452. Therefore, experimenters may expand on the application using the higher performance of the PIC18 family of parts without changing the hardware. With care,engineers and home control enthusiasts can experiment with home automation using the MPLAB® ICD and MPLAB® ICD 2 development tools or in-circuit emulator. However, proper circuit isolation precautions must be taken to avoid damage to your computer or development tools. See Figure 1 and the warning note! WARNING: VSS or ground on the application circuit is tied to neutral of the 120 VAC. To safelyconnect your development tools or computer to the home controller, you must power it through an isolation transformer and leave wall ground (the green wire in most cases) disconnected. Any test instruments (such as an oscilloscope) that you hook up to the application circuit, should be powered through the isolation transformer as well, with wall ground disconnected. In addition, the entire circuitshould be enclosed within a suitable case to prevent unintentional contact with the mains voltage!

INTRODUCTION
X-10 is a communication protocol designed for sending signals over 120 VAC wiring. X-10 uses 120 kHz bursts timed with the power line zero-crossings to represent digital information. Plug-in modules available from various vendors enable users to create home automation systems byusing the AC wiring already installed within a home. Readers who would like an overview of the X-10 signal format may refer to Appendix A. PICmicro® microcontrollers can easily be used in conjunction with X-10 technology to create home automation applications. The specific PICmicro microcontroller (MCU) used should be selected based on RAM, ROM, operating frequency, peripheral, and cost requirementsof the particular application. The PIC16F877A was selected for this application because of its versatility as a general purpose microcontroller, its FLASH program memory (for ease of development), data EEPROM, and ample I/O. This application note discusses the implementation of X-10 on a PICmicro MCU to create a home controller that can both send and receive X-10 signals. The reader may implementthe home controller as is, or adapt the circuits and firmware to other applications. A library of X-10 functions is provided to facilitate development of other X-10 applications using PICmicro MCUs (see Appendix E). Operating instructions for the home controller are included in Appendix B.

FIGURE 1:

TEST SETUP WHEN USING DEVELOPMENT TOOLS
X-10 Board X-10 Lamp Module Oscilloscope X-10 LampModule X-10 modules and any test instruments should be plugged into the isolation transformer. To maintain isolation, leave ground disconnected.

Isolation Transformer Computer, development tools, and the isolation transformer should be plugged into the wall outlet.

 2002 Microchip Technology Inc.

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HARDWARE DESCRIPTION
An overview of the home controllerapplication hardware is shown in Figure 2. The hardware functionality of X-10 circuitry can be divided into four functional blocks: • • • • Zero-crossing detector 120 kHz carrier detector 120 kHz signal generator Transformerless power supply There are several application functions that are not directly associated with the X-10 interface. User interface functions are accomplished with an LCD display and...