En route to a smart home with the Z-Wave protocol

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Article from Issue 184/2016
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Whether you want to control your lights or water your house plants remotely, home automation is making inroads into nerd households. Z-Wave technology offers devices for reliable control – a quick Perl script gets you started.

Now that inexpensive mini Linux platforms like the Raspberry Pi are readily available, I can think of dozens of home automation projects I'd love to be working on in the near future. For example, how could I use my cellphone – while out and about – to check whether my surfing wetsuit drying device is still doing its job, and how could I switch it off when all the moisture is out? Is the front door really closed and locked?

I just love to whip up applications like this, and I have explored similar topics in the past. Regular readers may recall the – now somewhat dated – articles on an Internet-controlled power switch [1] and a weather-controlled plant watering system [2].

At the end of the day, the procedure for these and similar applications is always the same: A sensor measures a value, such as brightness or moisture, and reports the values to a controller, which then trips an actuator – say, a relay – which in turn switches on a lamp or a pump. At this point, you may be faced with the problem that the control unit is quite a distance away, and you need a wireless approach to transmitting the signal to the actuator. Or do you really want to have the controlling computer in your plant pot?

Standards Confusion

A number of more or less standardized technologies deal with this topic [3]. After years of disappointment with the X10 method, which is popular in the United States but uses an unreliable method of communicating over power cables, I recently discovered Z-Wave technology, which is widespread in both the U.S. and Europe. In addition to using a totally reliable wireless handshake protocol, it is also fairly inexpensive.

To get started, I purchased a Z-Wave-certified mini-controller by the name of Z-Stick [4] from Aeon Labs for $35 (Figure 1), along with a Smart Energy Switch [5] for switching electrical consumers for $24 (Figure 2).

Figure 1: The Z-Stick controller by Aeon Labs for plugging into a PC USB port.
Figure 2: The Z-Wave Smart Energy Switch receives wireless signals and switches electrical consumers on and off.

The Z-Stick is a USB dongle that plugs in to a PC USB port. The PC then receives data from sensors and forwards signals to actuators wirelessly via the stick.

Installing on Ubuntu

The USB dongle more or less installed itself on Ubuntu 14.04, which immediately detected the Z-Stick and created a new device entry in /dev/ttyUSB0, as you can see from the syslog entry shown in Figure 3.

Figure 3: Ubuntu immediately detects the Z-Wave USB stick after plugging in.

Because the entry belongs to root, as well as the dialout group, and the permissions are crw-rw----, you should run any scripts wanting to access the device under an account belonging to the dialout group. If you are not worried about which user account switches the devices on and off, you can relax the access permissions by typing

sudo chmod a+rw /dev/ttyUSB0

instead.

Getting Started

For my first steps in the Z-Wave communication universe, I went for the zwave_s Perl script, which a company called Bigsister.ch offers on its website [6]. After installing a CPAN module for communication on the USB port using cpanm Device::SerialPort, the script worked perfectly. Figure 4 shows the zwave_s add command initializing the USB dongle. It then outputs a message telling the user to push a button on the device it is about to control – this was the energy switch in my case.

Figure 4: The zwave_s script initializes the energy switch and then takes care of switching it on and off.

I complied, and zwave_s assigned the energy switch the number 3, as you can see from the output. I then typed zwave_s switch 3 on, and the USB controller sent a wireless signal to the switch. As if by magic, the controller switched on the electrical consumer plugged in next door. The stick's range is claimed to be 100 feet, but you'll get less if it needs to penetrate solid walls. I then typed zwave_s switch 3 off to switch the consumers off again and the plugged-in desk lamp promptly turned off.

On GitHub, there is a Perl project named p5-ZWave-Controller, although it is struggling and has not been maintained for years – "abandonware" sort of sums this up. Instead, I quickly put together a new CPAN module named ZWave::Protocol and uploaded it just before this issue went to press. Listing 1 shows a practical application of the module that switches the Aeon energy switch on and off [7].

Listing 1

zwave-test

01 #!/usr/local/bin/perl -w
02 use strict;
03 use ZWave::Protocol;
04 use Log::Log4perl qw(:easy);
05
06 Log::Log4perl->easy_init($DEBUG);
07
08 my $zwave = ZWave::Protocol->new(
09   device => "/dev/ttyUSB0" );
10
11 $zwave->connect or
12   die "Failed to connect to " .
13      $zwave->device;
14
15 my $node_id = 3;
16
17 for my $state ( 255, 0 ) {
18
19   $zwave->payload_transmit(
20     0, 0x13,
21     $node_id, 0x03, 0x20, 0x01,
22     $state, 0x05 );
23
24    sleep 1;
25 }

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