9.1 X-10

The X-10 technology was invented about 25 years ago by engineers with a Scotland company. Pico Electronics Ltd. of Glenrothes, Scot-land, was founded in the early 1970s for the growing electronic calculator market. Every time Pico began a new project, it was given an experiment number. Experiments 1 through 8 were increasingly more complex calculator Integrated Circuits (ICs). Experiment 9 was a project for a programmable record changer. This work was done for BSR (British Sound Reproduction). Experiment 10, therefore the name of X-10, was also requested by BSR to provide a wireless method of remote control for its equipment. It was determined that wireless over existing electrical wiring was better than other alternatives such as RF or Infrared. X 10 devices were first introduced to the U.S. market in early 1979 by a New York mail order electronics company. X-10 devices were also later available from Radio Shack (as Plug 'n' Power) and Sears. Today, many companies make X-10-based home automation devices, such as switch and lamp modules, available over Web sites and in electronics stores.

An X-10 switch module sends signals over existing electrical wiring to a lamp module. X-10 modules can be either adapters that plug into wall outlets or units that replace conventional manual devices. X-10 power line technology transmits binary data in 1-ms bursts of 120 kHz during these zero-voltage crossing points of the 60 Hz AC sine wave between positive or negative transitions. The zero-crossing point was considered as having the least noise and interference from other devices on the power line. For robustness, X-10 requires two zero crossings to transmit either a zero or one bit. Every bit requires a full 60-Hz cycle; therefore, the X-10 transmission rate is limited to only 60 bps. A complete X-10 command consists of two packets with a three-cycle gap between each packet. Each packet contains two identical messages of 11 bits (or 11 cycles) each. Therefore, a complete X-10 command consumes 47 cycles, which yields a transmission time of about 0.7833 seconds. Because signal bursts are operating in a relatively low frequency of 120 kHz, a capacitive coupling bridge between different phases of an in-house electrical wiring system might be necessary to minimize attenuations.

9.1.1 Operation Principles of X-10

During a particular transmission, an X-10 transmitter normally sends an address packet followed by a command packet. An X-10 address packet consists of a start code, a house code, a number code, the repeat of the same start code, house code, and number code sequence. An X-10 command packet has a similar structure except that the number code is replaced by a command code as shown in Figure 9.1. The number of 60-Hz sine-wave cycles is also indicated in Figure 9.1 above each corresponding code field on the left and a half of the packet on the right.

Figure 9.1. X-10 Packet Formats

A house code consists of 4 bits representing letters from A to P. A number code consists of 4 bits representing 1 through 16 followed by a 0 bit. An intended receiver is identified by the combination of the house code and the number code. For 16 house codes and 16 numbers, 256 receivers can be distinguished. A command code also consists of 4 bits, but it is followed by a 1 bit. A command includes the house code and a command code. The encoding of these different codes is summarized in Table 9.1.

The Hail Req is transmitted to see if there are other X-10 systems within listening range. This allows an installer to assign a different Housecode if a Hail Ack is received. Ext Code 1 is for data and control. The Ext Code 1 is followed by bytes that can represent analog data (after A to D conversion). There should be no gaps between the Ext Code 1 and the following data bytes, as well as no gaps between data bytes. The format and meaning of these data bytes can be defined based on particular applications. Ext Code 2 is for meter read and DSM. Ext Code 2 is also followed by data bytes with no gaps and is variable in length. Ext Code 3 has been assigned for security message, but its format has not yet been defined.

For all these house, number, and command codes, the 1 bit is a burst of 120 kHz on the first zero crossing followed by a silent zero crossing and the 0 bit is a silent zero crossing followed by a burst on the next zero crossing as shown in Figure 9.2. In particular, the 120-kHz burst lasts about 1 ms with a starting tolerance of 0.2 ms while a receiver opens its detection window for about 0.6 ms.

Figure 9.2. One and Zero Waveforms

Table 9.1. X-10 Code Table

House	Code	Number	Code	Command	Code
0110	A	01100	1	All Off	00001
1110	B	11100	2	All Lts On	00011
0010	C	00100	3	On	00101
1010	D	10100	4	Off	00111
0001	E	00010	5	Dim	01001
1001	F	10010	6	Bright	01011
0101	G	01010	7	All Lts Off	01101
1101	H	11010	8	Ext Code 1	01111
0111	I	01110	9	Hail Req	10001
1111	J	11110	10	Hail Ack	10011
0011	K	00110	11	Ext Code 3	10101
1011	L	10110	12	Unused	10111
0000	M	00000	13	Ext Code 2	11001
1000	N	10000	14	Status On	11011
0100	O	01000	15	Status Off	11101
1100	P	11000	16	Status Req	11111

The start code is defined a little differently and cannot be represented by either the 0 or 1 bit directly. It consists of bursts of 120 kHz on three adjacent zero crossings and followed by a silent zero crossing as shown in Figure 9.3.

Figure 9.3. The Start Code Wave Form

There should be at least three silent cycles, or 6 zero-crossing points, preceding a packet or in between any packets. Figure 9.4 shows an example of an address packet followed by a command packet with three cycles of separation. There are altogether 47 cycles of the 60-Hz sine wave starting from the start code of the address packet and ending with the command code of the command packet. These 47 cycles last about 0.7833 second. Some broadcasting commands, such as all lights off and all lights on, do not need a leading address packet and, consequently, require only 22 cycles to complete. These 22 cycles last about 0.3667 second.

Figure 9.4. An Example Packet Sequence

9.1.2 Implementations of X-10 Devices

To send packets, an X-10 transmitter needs to have zero crossing detection, packet formation, and bursts signal generation capabilities as well as user input and power supply functionalities as shown in Figure 9.5. Also shown in Figure 9.5, An X-10 receiver needs to have complementary zero crossing, bursts signal, and packet detection capabilities. An X-10 receiver also needs device address assignment, power supply, and external control functionalities. These external control functions can act as a simple or a variable output switch for a range of different electrical appliances.

Figure 9.5. X-10 Transceiver Architecture

An X-10 device can be implemented with a microcontroller, for these signal generation and detection capabilities, as well as a few discrete components, for power supply and external control functionalities. Figure 9.6 shows a schematic for a possible implementation of an X-10 lamp switch module. The power supply, V, is provided by the diode 1N4004, the Zener diode, and the 220-microfarad (µF) capacitor on the left side of the transformer. Bursts signals, after being amplitude limited by two 1N4148 diodes, are collected at the other side of the transformer by the microcontroller. Zero crossings can also be detected by the microcontroller through a connection to the power line via a limiting and rectifying network that consists of three 1N4148 diodes and two resistors at the lower-right corner of Figure 9.6. House and device codes are input to the microcontroller directly. The microcontroller sends a signal via pin 6 to the triac (BTA10) for the external lamp-switching function. Feedback about the status of the lamp switch is also provided to the microcontroller via pin 8. Some X-10 device manufacturers have used PIC16C5X microcontroller to provide cost-effective solutions.

Figure 9.6. An X-10 Switch Module Implementation Example

Transformers are used in X-10 transmitters and receivers to isolate the bursts signal from the regular power line voltage. On the other hand, microcontrollers operate on a regulated power supply of between 3 and 5 V. Therefore, bursts signal level from a microcontroller should be within a few volts. The bursts signal level on the in-house wiring can be a few times higher or lower depending on the transformer ratio.