BY MICHAEL SIMPSON
lines, but a brief overview may help you
to troubleshoot problems. X10 uses a
PLC technology, which stands for Power
Line Carrier. A 1 ms, 120 kHz burst is
transmitted near the zero crossing of
the 60 Hz AC signal. Two crossings are
required to form a single bit. To generate “1,” we need a burst at the first
crossing and none at the second, as
shown in Figure 2. Figure 2 also shows
the pattern is reversed for “0;” we need
a burst at the second crossing but not
the first. Things would get out of sync
very fast if we did not have some way of
starting the whole data packet. A
special start sequence is used. This
sequence is three 120 kHz bursts at
consecutive crossings followed by no
pulse, as shown in Figure 3.
After the start sequence, the next
nine bits represent the actual data
being transmitted. The first four bits
are the house code. The house codes
are represented by letters on the
actual devices to make it easier on the
consumer as in Table 1.
After the house code, the next
five bits represent the device code or
function to perform as shown in
Table 2. The last bit is actually used to
indicate that the device is to perform
a function if the bit is 1. The complete
message from start to finish is sent
twice for redundancy.
In reality, there are variations to the
above protocol such as sending extended data, but I won’t be getting into these
in this article. Let’s start to break down
the various RS-232 interfaces. Each has
its own protocol and will translate your
interface data into the
X10 protocol I just talked
about. It isn’t necessary
that you understand the
actual details of the X10
protocol, just that you
know how the House,
Devices, and Function
codes are laid out.
All the previous
examples show a single
pulse that is synchronized with the zero
crossing. In reality, the
■ FIGURE 3
X10 specification
calls for three
pulses to be transmitted to make
the X10 compatible with a three-phase distribution
system. The second pulse is sent
2.778 ms after the
zero crossing. The third pulse is sent
5.556 ms after the zero crossing.
• PalmPad Remote Control (HR12A)
FireCracker
(Model CM17A)
I recommend the CM18A kit if
you don’t already have a wireless
Let’s start by looking at the
FireCracker (Figure 4). Due to its price
and simplicity, and the fact that it has
been around for a long time, there are
many of these in use today. The
FireCracker is manufactured by X10
and can be purchased as an individual
module or as part of the CM18A
package. The cost for the CM17A will
run you $12 to $40, depending on
where you purchase it.
The CM18A package shown in
Figure 5 is priced in the range of $22
to $39 and consists of the following
modules:
• FireCracker
Module (CM17A)
• Transceiver
Module (TM751)
• Lamp Module
(LM465)
■ FIGURE 4
A 0110
B 1110
C 0010
D 1010
E 0001
F 1001
G 0101
H 1101
I 0111
J 1111
K 0011
L 1011
M 0000
N 1000
O 0100
P 1100
■ TABLE 1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
All Units Off
All Lights On
On
Off
Dim
Bright
All Lights Off
Extended Code
Hail Request
Hail Acknowledge
Preset Dim
Extended Data
Status On
Status Off
Status Request
■ TABLE 2
01100
11100
00100
10100
00010
10010
01010
11010
01110
11110
00110
10110
00000
10000
01000
11000
00001
00011
00101
00111
01001
01011
01101
01111
10001
10011
101-1
11001
11011
11101
11111
April 2007 33
