My home automation system

Last updated 3/31/20


(This page is just kind of a starter.  Lots more details need to get filled in.  A better description is being started on my Project Notes pages here.)


The system that collects the data displayed on the front page of this web site has been under development since late 2008 (with no end in sight :-)  Its main purpose is to let me see how the house is doing when I'm not there – especially when we're on vacation.


Collection/control network

There are currently about 10 data collection/control nodes on an RS-485 network running all around the house (and out to the garage) at 57Kb over Cat5 cable.  Three pairs carry unregulated 9VDC to power the nodes; the other pair is the (half-duplex) data.  Everything is just wired in parallel.


The old nodes run PIC 16F628s; the majority are now Arduino based.  Some talk I2C to LM75 temperature sensors, some just sense data bits, as with the rain sensor and sump cycle sensor.  Some have output bits that can control stuff.  Ones that have wires that could get ground referenced (like water sensors on the basement floor) have opto-isolators between the external sensor and the local processor.  The one that reads the water meter has  a long and "interesting" history.  Some notes here.


The master/slave protocol on the wire is locally designed since it is not expected to talk to anything else.  (Sounds like famous last words.)  It's basically a sync byte, from addr, to addr, opcode, length, data, checksum.  The master polls each of the nodes (currently once/min) and the addressed node replies with its latest info.  Data – both length and meaning - is device dependent, so the master program has a decode callback for each device – identified uniquely by its address.  The protocol allows the master to send data to the slave nodes so it can use them to control external devices.


Currently four nodes use that control capability:  the router/modem power cycler, the sprinkler controller, the house water shutoff valve, and an inside/outside temperature/dew point display in the bedroom.  The first gives the computer a chance to try to fix loss of connection to the internet by power cycling the modem and main router, which occasionally gets confused.  Some details here.  The sprinkler controller lets the main computer control 8 channels of 24V valves that control watering of various parts of the landscaping.


Main collection program

Finally moved the main control perl program to a 5 watt pink Pogoplug from its earlier home on the main PC.  (Trying to host a mission critical application on a Windows machine is completely unworkable.  Don't get me started.)  It's responsible for polling the slaves, deciding when to give up on them, collects info for 5 minutes, then tries to send the latest to the web site.  It can send text messages to my phone for serious problems like sensor failures, extended power outages, water where it shouldn't be, etc.  Some details of the migration to the Pogo are here.


Control of the sprinkler system is driven by a perl module that reads a crontab-style control file.  On the list for years has been using the system's knowledge of rain and temperature and a new soil moisture sensor and maybe insolation to let it modulate the watering intelligently.  Someday.  That same cron-type system  now  also extracts special data from  the stdout logs, writes timestamps to make logs easier to read, etc.  Of course  the real system cron currently controls 9 other tasks, with lots of commented-out leftovers.


There is a little web server on the Pogo, and it would be nice if I could serve the main stats page from there as a backup to the web host.  No progress on that yet.  The web server (and sshd!) are visible on non-standard ports from the Internet.  I'm using a dynamic DNS mechanism for that.  It does host a day's worth of security cam pictures, tho.



The whole system – and especially its ability to sense and report power failures obviously doesn't work well if the computer or network/internet connection go down if power goes out.  The UPS is a big, old, ugly sine wave UPS/power conditioner retired from work.  The two 12V gel cells that used to live inside it have been replaced with two large marine deep-cycle batteries sitting next to the UPS.  It's ugly, but it keeps the computer and router and modem up for maybe 3 hours of power outage.


Unfortunately, the UPS doesn't have much intelligence.  It has a contact closure when it shuts down, but that's not a useful warning.  On the list is a battery voltage monitor that should let me shut the main PC and monitor (the biggest power hog) down gracefully while there's still lots of battery left to keep the Pogo, modem, and router up.  That monitor – which needs to be opto isolated from the network, since there's voltage relation between the battery terminals and the output AC – will talk to the PC over the 485 network.


Interestingly, the batteries are protected from lack of maintenance by – my backup sump pump!  That has a sensor and an alarm for "needs water" which beeps every couple of months.  As long as I have water and tools out to fill that one, I always fill the UPS batteries as well.

That sump pump backup is based on a Basement Watchdog 'Big Dog' system with which I have a love/hate relationship.  Its badly flawed charging system (which is a critical part of its job!) has caused me to buy unnecessary replacement deep cycle batteries as well as investing a huge amount of time and energy in monitoring the battery to protect myself.  It even has its own graph on the home page now!  I've come to believe my unit is just faulty and needs to be repaired (by driving 45 minutes to their shop).  The whole saga will be written up some day.


File transfer

The update data sent to the web site consist of one ascii line per sensor per sample.  The main perl program attempts an ftp of the latest updates every 5 minutes.  If it fails, the updates are remembered (in a file) and all will be sent when it next succeeds in connecting.


With both my previous and new hosting provider, there were occasional ftp failures which truncated the ever-growing file on the web host, losing all previous info.  That rarely happens any more, but the append-only file does grow to an unmanageable size, requiring manual intervention.  Over the years, I developed tools to warn me about that and make intelligently trimming the file fairly painless.



The main perl program currently can send me a SMS message by sending an email to my phone text address.  It alerts me if a sensor fails to respond 5 times in a row or if there's a power outage.  When the water sensors are in place, if they find undesired water that will certainly send an alert, too.  Note that this is dependent on my internet link being up!  I've vaguely considered a dial-out backup, but it isn't likely.


Ping stats to ISP

While it's not part of the 485 network, a separate perl program does a ping to the router at my ISP that my modem connects to every 5 seconds and keeps round trip time stats.  This is mostly to detect whether the internet connection is OK.  It could go to a few other stable sites outside my ISP to get a better view.  The stats from that bit of perl are also collected by the main program and sent to the web site so I can see how connectivity has been.  The collection program notices when it thinks connectivity is bad – currently 20 consecutive missed pings – and sets a flag that tells the main perl program to tell one of the 485 nodes to power cycle the modem and router.  There's some detail here.


Web site software

I found some php software that can produce graphs with auto scaling, etc.  Some more php reads the datafile and gets the data to feed the graphs.  The datafile analyzing software bucketizes the one-minute data into something that makes for smoother graphs.  It's a 'work in progress'.

It used to have some config options on the front page, but that let some damn Pakistani hackers in to trash the site.  After cleaning up that mess, I locked it down a lot more.  If I want the display different, I can ssh in and change it that way.


There's a watchdog that alerts me if things go wrong: the web host doesn't get an update for a while, file size is too big, graphs are stale, security cam pics are stale, etc.  After a few years' battle to keep my watchdog process running in the background (hosting providers don't like that) I finally found I could make it cron-based, and it's been stable for years now.  That watchdog can send email or - via email - text messages.

I just recently succeeded in using wget on the web host to get a nice ascii table of rainfall as recorded by the USGS at Salt Creek here in Elmhurst.  That data is taken every 5 minutes – just like mine.  It's integrated with the current rainfall info from my hardware as another line on the rainfall graph. It languished on the list for many years, but it's finally in place.


I would really like to change the back end to maybe a real database and do periodic data compression/purging of old data.  (I'll keep my one minute data for a while, but maybe reprocess to hourly (average + peak?) after 2 weeks or a month, and maybe daily after 6 months.  I still have the original one minute data on the PC at home.)  My new hosting provider (GoDaddy) supports mysql, so that makes it a little easier.  And maybe I can even get around the ftp failures/file truncations with transactions to the db!  The Round Robin Database tool looks pretty interesting, but I don't know if it will run on either the web host or the Pogo.

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