The CurrentCost power monitor has become very popular amongst amateur home automators and those technically-savvy who want to keep an eye on how much electricity they are using (and ultimately how much they are going to have to pay in bills). A couple of months ago I purchased the CurrentCost device and a USB cable to connect it to a computer from eBay. Having just seen their eBay store, it looks like they’ve got a fantastic new model on the way, but this article is about the older version.

By itself the device works very well, providing an at-a-glance view of current power use and a history over several periods of time. There is a simple bar chart showing the relative amounts of power used in the previous day, split into day time, evening and night. However if you want a clearer understanding of how power use changes day-to-day or even over a decade, connecting the device to a computer will provide the ability to store every reading in a database and/or produce live graphs of usage.

Several people have written articles on how to do the logging, each using a slightly different method (and language) to do so. Most of them are for linux though, but any programmer should be able to port the ideas across to a different platform such as Windows or Mac OS. For my implementation, I followed this guide on jibble.org.

This is what my perl script turned out like:

#!/usr/bin/perl -w
# Reads data from a Current Cost device via serial port.

use strict;
use Device::SerialPort qw(  ARAM :STAT 0.07 );

my $PORT = "/dev/ttyUSB1";
my $ob = Device::SerialPort->new($PORT);

$ob->baudrate(9600);
$ob->write_settings;

open(SERIAL, "+>$PORT");
while (my $line = <SERIAL>) {
    if ($line =~ m!<ch1><watts>0*(\d+)</watts></ch1>.*<tmpr>([\d.]+)</tmpr>!) {
        my $watts = $1;
        my $temp = $2;
        print `/usr/bin/rrdtool update /var/scripts/currentcost/powertemp.rrd N:$watts:$temp`
    }
}

Note that because I’m connecting via a USB port, the serial port name is different. The baud is also 9600 rather than 2800. I have set this script to run at startup (detatched from the console) so that it is always running in the background.

I have also produced another simple script, which is run every minute as a cron job.  The script generates the graphs from the data stored in the RRD file, and uploads them to my web server via SSH.

#!/bin/sh

rrdtool graph /var/scripts/currentcost/power-10min.png --start end-10m --width 323 --end now --slope-mode --no-legend --vertical-label Watts --lower-limit 0 --alt-autoscale-max DEF:Power=/var/scripts/currentcost/powertemp.rrd:Power:AVERAGE LINE1:Power#0000FF:"Average" > /dev/null
rrdtool graph /var/scripts/currentcost/power-60min.png --start end-60m --width 323 --end now --slope-mode --no-legend --vertical-label Watts --lower-limit 0 --alt-autoscale-max DEF:Power=/var/scripts/currentcost/powertemp.rrd:Power:AVERAGE LINE1:Power#0000FF:"Average" > /dev/null
rrdtool graph /var/scripts/currentcost/power-day.png --start end-24h --width 323 --end now --slope-mode --no-legend --vertical-label Watts --lower-limit 0 --alt-autoscale-max DEF:Power=/var/scripts/currentcost/powertemp.rrd:Power:AVERAGE LINE1:Power#0000FF:"Average" > /dev/null
rrdtool graph /var/scripts/currentcost/power-week.png --start end-1weeks --width 323 --end now --slope-mode --no-legend --vertical-label Watts --lower-limit 0 --alt-autoscale-max DEF:Power=/var/scripts/currentcost/powertemp.rrd:Power:AVERAGE LINE1:Power#0000FF:"Average" > /dev/null
rrdtool graph /var/scripts/currentcost/power-month.png --start end-1months --width 323 --end now --slope-mode --no-legend --vertical-label Watts --lower-limit 0 --alt-autoscale-max DEF:Power=/var/scripts/currentcost/powertemp.rrd:Power:AVERAGE LINE1:Power#0000FF:"Average" > /dev/null
rrdtool graph /var/scripts/currentcost/power-year.png --start end-1years --width 323 --end now --slope-mode --no-legend --vertical-label Watts --lower-limit 0 --alt-autoscale-max DEF:Power=/var/scripts/currentcost/powertemp.rrd:Power:AVERAGE LINE1:Power#0000FF:"Average" > /dev/null

#Copy locally
cp /var/scripts/currentcost/*.png /var/www/currentcost/

#Upload to mars
/usr/bin/scp /var/scripts/currentcost/*.png root@192.168.2.3:/var/www/vhosts/currentcost.elemental.killswtch.net

You can see the result on the Power page of this site. The graphs at the moment are fairly basic. The Jibble article includes some extra data in the graphs, which I will probably add at some point. For the moment though it does the job very well.

The CC device is located downstairs, in the living room. Thanks to the serial output connector being an RJ45 socket, it was very easy to plug it into the exising CAT5 network (which I’m very glad I did) and run the signal to the cabinet in my room where it is then broken out through the RJ45 patch panel, through the RS232/USB cable and into the fileserver boron, which hosts the scripts.

Over a year after it began, the whole-house-audio project is complete. 4 rooms around the house can now be filled with the sound of any of (currently) 4 audio devices thanks to a mixture of hardware and software.

The project had a slightly rocky start, with a prototype not functioning at all and partly destroyed amplifier (which was thankfully fixable by replacing a couple of components). A software alternative was considered at one point, to avoid too much expensive hardware. The hardware solution proved to be less complex and more likely to work.

The living room, dining room, kitchen and master bedroom are host to a pair of speakers each, connected to matching 240W rack-mounted amplifiers housed in my home-made full-height 19″ rack cabinet. The cables that carry the audio signals to the speakers were installed along with 24 runs of CAT5 before moving into the house.

The audio is routed to the amplifiers via an 8×8 VAMS-0808 AV matrix switcher, which allows the 8 outputs to take their inputs from any of the 8 available sources. Only 4 of each are currently in use, so there’s plenty of room for expansion.

4 audio sources are connected via simple custom-altered CAT5 cables, which simply transmit line-level signals over the existing twisted pair infrastructure installed in the house. These sources are currently the DAB radio in the kitchen, the TV in the living room, the computer in the dining room (for playing CDs) and a second DAB radio in the master bedroom.

I’ve written the software to control it all using .Net (C# of course), running on mono on linux. There are four components to this:

1. To control the matrix switcher, I have written a library which communicates with the VAMS-0808 via an RS232 serial connection. The software can perform any of the operations that can be performed via the front panel of the device, apart from switching power on and off.
2. The amplifiers are connected to an APC AP9212 MasterSwitch Power Distribution Unit which was bought with this project in mind. Controlling this is slightly less straightforward and not quite as elegant. The library that I’ve written for this communicates through the telnet interface of the MasterSwitch to turn devices on and off.
3. Combining these two libraries is a simple web server which presents an equally simple XML-based web service. The service allows room inputs to be changed and switches the amplifiers on and off as necessary. This runs on a low-power disk-less computer running Ubuntu, hidden within the rack cabinet.
4. A touchscreen web interface acts as a front-end to the entire system. The simple menu system uses iUi for a clean touchscreen-friendly design. As with the web server this runs on a low-power machine, although this one has a small hard disk and runs Windows due to technical issues with the touchscreen.

There is currently just the one controller front-end, located in the dining room. To listen to the kitchen radio, for example, all that is necessary is to select the ‘Kitchen DAB Radio’ option from the main menu, then select which of the 4 rooms to play it through – or all of them if you are going to be wondering around most of the house.

Future extensions

Thanks to building the web interface with iUi, the system is compatible with the iPod Touch and iPhone, so they can instantly act as frontends for audio control. A second fixed controller may be added in the master bedroom in time, if there’s enough money available. Each front-end costs about £200 in hardware, depending on what bargains can be found on eBay.

The matrix switcher supports both audio and video. Only the audio channels are used at the moment, so there is the very real possibility of using the remaining 4 output zones to connect to TVs around the house and adding some AV sources. This way it’s instantly converted into a whole-house-AV system. The video signals can be carried over the twisted pair CAT5 cables like the audio, but will require a little more hardware to preserve quality. This hardware is relatively expensive, although savings can be made by building the equivalents by hand. Following the tradition of this project, that’s probably what I’ll do. I have done it before while I was at university and it works beautifully.

One thing that has been lacking since the first build of the rack is ventilation. With both sets of doors closed, the inside can get quite warm, especially when iron is turned on. Not any more though, having just completed the installation of 2 active ventilation zones, lighting and a low voltage power supply system complete with rack-mount control panel.

Air is drawn in at the bottom of the rack by 5 quiet 80mm 12v fans, positioned behind a perforated 2U panel inside the front panel of the base. The air is blown vertically into the cabinet from the bottom through a similar 1U perforated panel. Although the draught is barely noticeable, the difference it makes to temperatures at the front of the rack is significant.

With this ‘air curtain’ alone though, the back of the rack still gets very warm. To solve this I’ve installed a relatively huge 200mm ‘Big Boy’ fan into the newly-added top of the cabinet. This sucks out the warm air and dispenses it into the containing room. Together these fans keep the entire cabinet cool.

To power the fans I’ve used an old ATX power supply. In order to make replacement easy when the supply fails, no modifications have been made to it. Instead, I bought a 20-pin molex connector so that I could just plug the ATX connector straight into my system.

The PSU is connected to 4 switches that are mounted on a 1U blanking panel in the front of the rack. I wanted some fancy switches, so I splashed out on some nice chromed illuminated ones from China (via eBay). There’s one green DPDT switch, which switches the PSU on and off, and three blue SPDT switches which control power to the two fan systems and some lighting.

The lighting illuminates the front of the rack, and is there purely for decorative purposes. I had considered using cold-cathode tubes, but the seller that I got the switches from also sells strips of LEDs encased in a flexible transparent rubber-like substance. They are sold in various lengths, but I thought 96cm would be OK for what I wanted (at the time I bought it to experiment with, thinking that it could illuminate the wall behind my desk). This strip is now mounted on the left-hand front door.

The audio system that I’m building requires 2 low-power computers: 1 for the touchscreen controller (not using an iPod Touch for the moment) and 1 to act as a webserver and serial-console server.

Once again eBay has come to the rescue, and by searching for ‘geode’ – a low-power processor for Thin Clients & Small Form Factor (SFF) PCs – I found the 2 machines that I needed. These are the specs:

magnesium (the black one)

• 800 MHz Geode
• 256 MB RAM
• 6 GB CF drive
• Onboard graphics, audio, serial, parallel, USB & 10/100 ethernet

£70 + P&P

potassium (the grey one)

• 300 MHz Geode
• 256 MB RAM
• 6 GB 2.5″ IDE drive
• Onboard graphics, audio, serial x2, parallel, USB & 10/100 ethernet

£35 + P&P

Magnesium is used as the client machine, and potassium runs a custom-made webserver and the control software for the VAMS-0808 Matrix Switcher.

Both came pre-installed with Puppy Linux, a lightweight distribution designed for low-power machines such as these. It runs surprisingly quickly, but to make it easier for me to maintain I decided to install Ubuntu.

On such slow computers it took many hours to get Ubuntu installed on magnesium alone. I initially installed to the CF drive that came with the machine. However I found it to be quite slow, so I followed a guide for running Ubuntu via network boot and removed the CF disk. I did the same for potassium. Both booted off of the fileserver, boron.

Unfortunately during installation, I found that the slower of the machines has a tendancy to overheat causing the machine to hang. To get Ubuntu installed I had to remove the case. This has now been rectified by installing a blower to get at least some air circulating. This is the only fan in either of the machines. Magnesium gets quite hot but has never crashed because of it. It also sits in a cooler environment, and is much better engineered.

Sadly I’ve been forced to install Windows XP on magnesium purely because I couldn’t get the touchscreen to work under linux despite spending more than a day trying to. While it was detected, and it detected touches, the calibration was completely off and there was no way to configure it. Rather than waste any more time I decided to switch to Windows and everything has worked beautifuly since then. To accomplish this I’ve had to reinstall the CF disk since as far as I know XP Pro can’t do diskless booting.

Shots of these computers in use and more information on their roles to come soon.

• Digital terrestrial, received through a suitable TV antenna (DVB-T)
• Cable, in most cases through Virgin Media (DVB-C)
• Sky (DVB-S)
• Freesat (DVB-S/DVB-S2)

My MythTV installation is currently solely using a dual-tuner DVB-T receiver to record TV. However we are right on the edge of the closest transmitter’s reach with no usable overlap with any other transmitter, so at best our signal is spotty.

As spring progressed and the trees regained their leaves our signal has gotten weaker and weaker to the point that about 90% of recordings fail due to a lack of a signal lock or a very weak signal producing something that’s unwatchable.

The TVs in the house cope slightly better, but still suffer a lot from a broken signal. With digital being all-or-nothing compared to analogue’s degrees of static snow, it’s either you can watch something or you can’t… unless we change to the analogue tuners in the TVs, which we often have to.

We are being forced to consider alternatives, either to back up terrestrial or replace it completely.

I’m keen to keep to things which can be used legally with MythTV, which would rule out Sky and Virgin Media which essentially bind you to using their hardware. The benefits of those two services however is that they have a more complete selection of channels as well as the option to upgrade to significant bonus content, compared to the one remaining alternative – Freesat.

Freesat was launched recently by a collaboration between the BBC and ITV. Most of the transmissions are in Standard Definition (SD) with a small sprinkling of High Definition (HD) services. More channels are expected to sign up, but at the moment there’s all of the UK BBC and ITV channels plus Channel 4 but at the moment no Channel 5 (who seem to insist on transmitting encrypted signals). Also there are none of the UKTV-owned channels including Dave.

Freesat is transmitted unencrypted over DVB-S & DVB-S2, both of which can be received by a computer using an appropriate satellite receiver card. Naturally I’ve been keeping my eye out on eBay for such cards, and there are usually a few on at a time. I’ve not bought any just yet and I won’t until a decision is made for sure that we’re going for Freesat rather than the next alternative, cable.

DVB-S2 is used for carrying HD programmes. It is relatively new, so although there are PCI cards out there cable of receiving the transmissions, the software for Linux hasn’t caught up yet. MythTV is in the early stages of including support, and some basic drivers are available. The cards come with software for Windows, but that’s not much use for a distributed MythTV-based PVR. I’m hoping that at least I can get DVB-S working for recording and such, then upgrade to DVB-S2 when it’s reliable. In the meantime HDTV can be watched on a normal set-top box.

Before Freesat came on the scene, as already mentioned the next alternative was cable from Virgin. In my investigations it quickly became apparent that connecting a DVB-C card (a rare thing in the UK) to Virgin’s cable network was not a good idea since it would almost guarantee disconnection of all services including my 20 meg broadband.

To keep within the T&Cs of that means using the analogue output from the V or V+ box, connecting it to a capture card and then doing digital->analogue->digital conversion. The result of this would be relatively low-quality video and audio, at a limited resolution (SD only). An IR transmitter would need to be used to control channel changing, and since it uses the only externally-available tuner you couldn’t watch one channel on TV and let another record on the same box. It’s certainly not an elegant way of doing things.

If we were to go for Sky, a similar thing would probably have to happen, although with a little work it may be possible to get a PCI DVB-S card to work with it, provided it had support for a decoder card so that the signal could be decrypted.

In the likely event that we decide to go for Freesat, the cheapest solution would be to do a complete self-install. However the easiest solution would be to pay for installation of a single-room service. We will need a 4 room service however, so the plan is currently to pay for a single room installation at £80, then buy a quad LNB and run the 3 other cables ourselves. That way we don’t have to worry about getting the correct size dish, mounting and positioning it. Apparently there’s some satellite-grade coax around somewhere that should do the job.

There will probably be 2 tuners in a machine that will do the recording (possibly boron) and the other 2 runs will go to the living room and the master bedroom.

Naturally there will be photos and such if/when the project takes place.

Yesterday I completed and successfully tested the control software for the audio system. The software works with the matrix switcher and the APC MasterSwitch remote control PDU to allow the audio output devices around the house (TV, radio, CD player etc.) to route their sound to any of the 4 audio zones.

I’m now waiting on some more purchases from eBay to arrive before I can finish the system off. On the way is a small touch-screen monitor and a low-power mini ITX computer to connect it to. This will function as the controller and will probably sit in the dining room at the centre of the house. I’ve not gone for an iPod just yet, since a small mobile device has the possibility of getting lost or damaged more readily than a fixed controller. I’m looking out for a cheap 2nd hand one on eBay though.

Although I had got the software working yesterday, I foolishly installed some updates for Ubuntu and now the serial ports have disappeared again. Rather than battle to get the ports to show up and behave I’ve gone a little more eBay crazy and bought a second thin-client-like low power PC which will run the matrix control software and possibly the web server for the front-end control interface.

The other remaining tasks include creating some more cables and positioning and attaching the speakers for zone 4, the master bedroom.

Full details of the setup, with a video, will hopefully be posted in the next few weeks.

The speakers for zone 2, the dining room, have been installed without much of an issue. They sound pretty good after a test of zones 1, 2 & 3 using the DAB radio in the kitchen. The left-hand speaker helps to hide the cable route from the pantry to the dining room & kitchen.

There are 4 audio zones in the house, each requiring it’s own amplifier and pair of speakers. I’ve just purchased the last of the amplifiers, which completes the selection of hardware that’s necessary within the cabinet. I took the opportunity to rearrange the order of things in the rack a little to tidy things up.

A recent electricity bill has prompted me to investigate how much power is being used by each device in and around the cabinet in the hope of figuring out what can be replaced to reduce running costs. I’ve had a power monitor from Maplin for a while, but most of the time it’s been monitoring total power consumption of the rack.

Power

• UPS: ~50W non-charging

Networking

• 24 port 10/100 switch: 25W
• 4 port 10/100/1000 switch: 18W
• 5 port 10/100/1000 switch: 8W
• Router: 3W
• Modem: 3W

Computers

• Boron (fileserver): 150-190W
• Aluminium (desktop): 250-295W
• Barium (HTPC): 66-85W

The audio system components haven’t been measured yet because at the moment they aren’t ready to drive a load and measuring the idle consumption wouldn’t be very meaningful. The amplifiers will be switched off when not in use and won’t be used that much compared to the items listed above.

Based on the data above, I have replaced the 3 switches with 1 switch. I have been investigating replacing boron with a collection of NAS devices for storage and a low-power ITX-based machine for services such as DHCP and DNS. However this is currently quite an expensive option.

Aluminium is a gaming-spec PC so will always consume quite a bit of power, however I’ve got some software under development which should mean that I won’t need to keep it on to download the occaisional torrent – that job could be offloaded to boron or my hosted server.

Barium is only on when I want to watch a DVD, a video or recorded TV from MythTV. It was specced to be quiet and consume as little power as possible with a Core 2 Duo CPU, 1GB DDR2, a passively cooled HDCP-capable VGA/DVI graphics card and a quiet PSU.

I’m going to continue to look at reducing consumption not just in the rack but around the rest of the house.