System integrity and home automation
What IS the problem ?
Whether it is the HVAC controller, the hardwired alarm system, the
home automation controller, or just one of the lamp modules,
sometime IT IS GOING TO FAIL.
Obviously, quality pays off by lowering the probability of failure.
However, even those devices which cost the most and are scrupulously
maintained still do fail. ( like at Kennedy Space Center ).
Regardless of the amount of money you put into your system, you
cannot have absolute reliability without an alert and caring human
included as an integral part of your system.
Whether that person is you or a paid guard, you cannot assume that
your system is functioning properly unless you periodically verify it
With the addition of a computer into the equation, we now have
another controller which can test the reasonableness of the other
systems and augment their behavior.
We can also very carefully craft a system which has 'holes' in its logic.
You can make things which you think are perfectly reasonable, but have
operational or logical problems. And the controller can 'hang' or fail.
The more complex a system you create, the more difficult it is to verify.
Think about how you want your system to behave, how you want to
expand it, and re-think it often.
What's the probability?
Although it would be possible to spend enough time calculating the
probability of failure of any complete system, it would be very costly.
There are too many variables.
Because the devices are usually inexpensive, most users just replace
them and never say anything. This makes it difficult for device
manufacturers to publish any MTBF figures.
The best thing that can be said about X-10 world is that they have sold
many millions of devices and that there is a large community of
advocates who use and install them. If they were really flakey, there
wouldn't be a market.
The probability is that you will find some devices which are dead on
arrival or die soon, and some which last for 10 years or more through
lightning and rain.
Generally, if a device performs for the (warranted) first year, it will
probably last for a very long time. If it's going to die, it will likely
do so early in its life.
How do you build a reasonably reliable system?
Buy quality devices.
Although almost all of the X-10 compliant devices are manufactured
in the same Chinese factory, there are differences in the production
specifications for each of the private labels.
These differences are generally not published, but it is known that
they involve such things as component quality and how well each
unit is tested.
In general, you should expect that brand names which are known to
be better quality will be better tested. Any 'bargain' devices you buy
probably are known to have come from 'weak' batches.
This does not mean that the better quality devices won't fail, nor that
a 'bargain' module won't work for 10 years. Buy the bargains if you must,
but buy several at a time. Odds are that some of them will be real keepers.
Use existing controllers for specific subsystems.
Many homes already have a HVAC system which is reliable and simple.
Many homes already have a standalone burglar system, and most of these have
some type of monitoring $ervice.
Although you can eliminate all of these functions with your home
automation system (XTension); by doing so you would be creating a
'single point of failure' in your system.
By orchestrating all of the above into a single system, you can
improve the probability that your system will survive Murphey's
ie: More devices = more potential failures, but if you are really interested
in integrity, you want to know when anything in the system fails.
Use the systems you have already. Monitor them and announce what you can
about any significant changes.
Don't be disturbed by too many alarms.
You certainly don't want the system to be annoying, but you surely
want the system to be "a little bit more critical than it needs to be",
rather than a little bit "less"... It follows that you are going to have
to put up with some 'false alarms'.
Pay attention to your system:
(Don't get caught by the "boy who cried 'Wolf!' " syndrome.)
Centralize the monitor function-(Work with the existing controls.)
The home automation system can provide the central control and
monitor function. With simple X-10 input/output devices you can
both sense behavior of those subsystems and issue simple commands
By integrating these subsystems into your home automation system,
you can watch and log their behavior and even interact with them.
Ok, How ?
A common output device from X-10 is the 'Universal Module'.
Connect two wires from the screwposts of this module to any system
which is triggered by a 'contact closure'. You can then send X-10
ON/OFF commands from (XTension) which are received by the Universal
Module and translated into a contact close/open. Your HVAC or alarm
system can then detect the change and react accordingly.
A common input (sensor) device is the 'PowerFlash' from X-10.
By connecting the input screwposts of the module to the low-voltage
output of your HVAC system, you will get a X-10 ON/OFF message
whenever the blower cycles (for example).
You might want multiple sensors if you have multiple zones etc.
The same can be done with the outputs of your alarm system. Most
systems will provide some simple signal which indicates that alarms
have occurred or that the system has been disabled.
You can expand your home burglar system by having the home
automation system monitor add-on sensors and conditionally send
commands from XTension to the alarm system to 'set panic mode' etc.
You can do the same with your HVAC system, adding duct
controls, booster fans and set-back controls.
Redundant home automation computers
If you have two or more computers, then you can have redundant
systems. You also need two X-10 controllers.
Set up one to assume that it is the master, and the other to assume
that it is the backup.
The backup always monitors the behavior of the master, and if the
master fails, the backup can take itself out of 'monitor' mode and take
over control of the system.
The backup would then try to restart the master, and on discovering
that the master is again in control, the backup would put itself again
into 'monitor' mode.
All of the above can be done easily with the Macintosh, AppleTalk,
Good thoughtful 'feedback'
You must incorporate 'feedback' into your system such that whenever
you issue commands, you should always 'see' some response, regardless
of the current state of the system.
For example, you're going to bed and the lights are already off. You
signal that you are going to sleep, and the system has failed or fails
to receive your signal.
If you don't see a lamp come on and go off, or something then how
do you know that you should go to sleep yet?
You can easily create scripts which always 'toggle' a lamp next to
you whenever you issue such commands.
You should always 'see' some response from every command that
you give to the system.
Avoid setting addresses of units such that they are controlled directly
Always have the computer control things, and you will always
have good acknowledgement of proper system health.
For example, set a lamp to A1. When you want to control the
lamp, you use address A2 (or P3, it doesn't matter). You provide
scripts which respond to commands for A2, by controlling the lamp
on A1. ( XTension lets you give reasonable names to these units )
Some elements of the system can continue to function through
'brown-outs', but ultimately on longer outages, the batteries will
Because brown-outs are more likely, the use of a battery is specially
Your home automation system can detect long term outages and can
perform any necessary scripts for notification, log the event, and then
shut down softly.
Use of a battery-backed powerbook is both a blessing and a pain.
Although some can suffer very long power outages, it is very difficult
to restart one after it has 'hung'.
If you use a laptop, make it the backup controller.
Thus if the master is not battery-backed, and is plugged in to a X-10
appliance module, the standby machine can turn off the master if
the power is on and the master is not responding to normal
If the standby detects that the master has 'hung', but the power is still on,
then it takes over control of the system and attempts to restart the master.
Once the master has assumed control, the standby resumes its monitor
If the standby detects a power fail, it assumes that the master has failed
also. It continues to monitor the status of the power.
When power is restored, the 'backup' immediately assumes control of the system
and then looks for the master to complete initialization. After which the backup
assumes its normal monitor role.
All of the above can be done easily with the Macintosh, AppleTalk,
Simplicity versus bother
No solution should create a problem greater than the problem it is
supposed to solve.
Don't create a system which is so complex that it becomes a bother to
The more complex the system, the more prone it is to failure. The
greatest chance for 'failure' is that the system is in-completely
Although you can create very complex and solid systems, it takes
thought and testing. Don't scrimp.
Frequent system checks by a caring human
You should have a procedure that you perform frequently which
verifies the proper behavior of all critical units.
Prompt maintenance of any failed device or program
Don't let the system deteriorate, it will become a liability.
If something can't be fixed promptly, it should be disabled so that it
doesn't become a confusion to the rest of the system.
Keep spares handy.
Really, you like the system, keep it up.
Buy better quality devices
Use multiple autonomous controllers
Use redundant home automation controllers
Check the system often
Incorporate feedback in your system
Be aware and tolerant of controller speeds and wireless
Maintain everything in top condition