The manufacture of batteries is a very energy intensive process often using many types of heavy metals, it makes total sense to use rechargeable batteries where possible and always recycle old batteries. When it comes to low power sensing nodes I’m as guilty as anyone else when it comes to just sticking in some cheap alkaline batteries, always believing that the performance of rechargeable batteries was much lower. This is not the case anymore.

If rechargeable batteries are used (which they should be) the self-discharge rate can be significant. The self-discharge rate of NiMH batteries is high: around 30% per month at room temperature. This problem can be almost eliminated by using low-self discharge NiMH cells such as Eneloop, they have a discharge rate of about 5% per year. If non-rechargeable alkaline batteries are used they have a self-discharge rate of less than 2% per year.

Rechargable batteries self-discharge graph from batterydata.com

If you care about the environment (which we all should do) we highly recommend the use of Sanyo Eneloop rechargeable AA’s in the emonTH and emonTx. They are a bit more expensive (about £2 each) but over their lifetime (they can be recharged 2100 times!) they will work out cheaper. The Eneloop cells are cadmium free and arrive fully charged and ready to use. Sanyo states that this charge is supplied by their solar PV system in Japan!

An excellent setup (as recommended by JCW of JeeLabs.org) is a spare set of Eneloop AA’s (Apple AA’s are rebranded Eneloops) permanently plugged in an Apple AA charger which he measured using 0W when the batteries are fully charged! This way you always have a set ready to go: http://jeelabs.org/2010/08/19/new-aa-battery-option/

Update: I’ve just discovered iGogreen’s Alkaline Rechargeable batteries which claim to hold their charge for 7 years and contain no heavy metals : Mercury, Cadmium, Lead or Nickel. They do fall down for high power draw applications but this is not an issue here, maybe a perfect match for long term low power nodes? They are also cheaper than Eneloops. The only draw back is they they need a special charger, iGo do a reasonably priced nice looking USB charger which will also charge standard NiMH

Update #2: The iGoGreen rechargable alkaline AA’s tended to leak acid after a couple of years. I would not recomend. They seem to have now been discontinued

After much re-arranging we've got the new date for the energy monitoring build weekend that we're hosting with Carbon Coop at MadLab in Manchester. Its now on the 16th and 17th of November.

Meetup page:
http://www.meetup.com/Eco-Home-Lab-Manchester/events/140046162/ 

As before there will be three main parts to the weekend:

Build an OpenEnergyMonitor system (Saturday 10AM - 6PM + Completion on Sunday if needed)



This is a chance to build a monitoring system with the support of others who have built systems before, Matt Fawcett and I will be on hand to help, we will walk through building the emontx energy monitoring sensor node and how to setup a raspberrypi basestation running emoncms.

With this you can explore and track changes in home electricity use over time via a web dashboard.



If you've already got an OpenEnergyMonitor system but need some help getting it to work your also welcome to attend this workshop, please bring your monitor along.

To complete the build you will need:

• Emontx 868Mhz
• Programmer - USB to serial UART
• Mini USB cable
• USB power adapter
• AC-AC Adapter - AC voltage sensor
• Raspberry Pi - model B
• RFM12Pi Raspberry Pi Expansion board kit 868Mhz
• Micro USB Cable
• USB Power supply for RaspberryPI
• Sandisk SD card for the Raspberrypi
• 1 mtr cat-5 cable

The total build price if you get everything from the OpenEnergyMonitor shop is £121.5 inc VAT.

If you already have a raspberry pi and spare USB Power supplies, micro and mini USB cables (they often come with newer mobile phones) you can do the whole build for £68.50.

There will be a limited number of these kits available on the day (at the same cost), to make sure you can build please order these beforehand.

Put a note in your order message that you need the kits for the weekend so that we can make sure you have them.

If you want to read-up on the build guides and learn more about the system before the event take a look here:

http://openenergymonitor.org/emon/guide

Show and tell
 
Were excited that Robin Emley will be joining us to demonstrate his Solar PV Diverter on the Saturday: 
http://openenergymonitor.org/emon/mk2

If youd like to come and show what you've been working on around open source monitoring and control please do, get in contact to let us know if you are coming.

Hackathon
There will be a table dedicated to just developing something new, hardware or software. For example editing or amending the monitor's online display dashboards or improving energy modelling tools such as OpenSAP.

Sign up on the meetup page
Please add your name to the meetup page if your coming so that we have an idea about numbers and let us know how much of the kit you want for the build as above.
http://www.meetup.com/Eco-Home-Lab-Manchester/events/140046162/

We look forward to seeing you there! please get in contact if you have any questions:

[email protected] or [email protected]

In the interest of open-source I thought I would share the backup setup we have running for the OpenEnergyMonitor website. I'm relatively new to sys-admin tasks and writing bash scripts so please suggest if you think if something could be implemented better.

Backing up our Drupal SQL databases which contain the user credentials and all the forum and text content of the website was relatively easy since the disk space they take up is relatively small. A nightly SQL dump then a scheduled secure FTP bash script running as a nightly cronjob on a Raspberry Pi with external hard drive to download the zipped SQL database does the trick. The FTP login credentials are stored away from prying eyes in .netrc file (with chmod 600), two sets of credentials are required and the relevant .netrc file is copied to the home folder when needed.

cp netrc/.netrc1 .netrc
today=$(date +"%d-%b-%Y")
ftp -vp -z secure $HOST << EOT
ascii
cd /LOCATION OF SQL DUMP ON SERVER
get $db_name-$today_backup.gz $LOCAL_BACKUP/$db_name-$today_backup.gz
bye
EOT
rm .netrc

 Backing up the files (images, documents etc) is a bit more of an issue since the ever increasing size of the content mean it's impractical and would unnecessary load the server and bandwidth to download a full snapshot every night.

I found wget has many customisable options. A nightly scheduled bash script running on a Raspberry Pi with an external hard drive with the following wget options looks at files have been created or modified since the last time the command was run and only downloads the changes. Once the initial download is done the command only takes less then a minute to execute and often only downloads a few Mb of data. The option '-N' tells wget only to download new or modified files

cp netrc/.netrc2 .netrc
wget -m -nv -N -l 0 -P $LOCAL_BACKUP ftp://$HOST/public_html/FILES_LOCATION -o $LOCAL_BACKUP/filelog=$today.txt
rm .netrc
# This is what the other options do:
# -l 0 infinite level of recursive (folder depth)
# -m mirror
# -N only download new files
# -o logfile
# -b run in the background
# -q turn off logs
# -nv non-verbose logs

This setup seems to be working well. It has a few weak points and limitations that I can think of:

• The wget files backup script only downloads new and modified files, it does not mirror the fact that a file could have been deleted on the server, the file would remain in the backup. 

• The wget script does not keep historical snapshots meaning that if something bad was to happen it would not be possible to rollback to a certain date in history. Update: I have since had recommend to me Rsnapshot which is a backup utility based on Rsync. Rsnapshot looks great and can work over FTPS. My friend Ryan Brooks wrote a good blog post on how to set up Rsnapshot over FTPS. 

• Currently the Raspberry Pi only has the one external 1TB hard drive used for backup, ideally this would be two hard drives in a raid array for double safety Backups are only done nightly, this is plenty good enough for us at the moment but might need to be improved in the future. 

I think it's amazing that a little £25 Raspberry Pi is powerful enough to handle backup for several websites. the Pi with an external 1TB hard drive connected through a USB hub consumes only 5.7W making it not too bad to leave on 24/7.

 One issue that I had initially with the Pi is that the external hard driver would move from /dev/sdb to /dev/sdc therefore loosing it's mount point. I think this was caused by the HDD momentarily losing power. Switching to using a Pimoroni PiHub to power the setup and mounting the drive by it's UUID instead of /dev/xxx reference in fstab fixed the problem: 

UUID=2921-FCE8 /home/pi/1TB vfat  user,umask=0000   0   0

I would be interested to hear if you think how the backup could be implemented more efficiently or more securely.

1) Install emoncms on your backup machine following the guide here: http://emoncms.org/site/docs/installlinux
Create an account and note down your mysql credentials.

2) Download the usefulscripts repository
https://github.com/emoncms/usefulscripts

There are two scripts available under usefulscripts/replication

• import_full.php
• import_inputs.php

3) Try importing your inputs first to test that it works: Open to edit import_inputs.php.
Set your mysql database name, username and password, the same credentials as for the settings.php step of the emoncms installation. Set the $server variable to the location of the raspberrypi or emoncms.org account you want to backup and set the $apikey to the write apikey of that account.

In terminal, goto the usefulscripts/replication directory. Run import_inputs.php:

    php import_inputs.php

If successful you should now see your input list and all input processing information backed up in your local emoncms account.

4) Backup all your feed data:

As for importing inputs open import_full.php and set the database credentials and remote emoncms account details.

Run the backup script with sudo

    sudo php import_full.php

That's it, it should now work through all your feeds whether mysql or timestore (no phptimeseries support yet) making a local backup. When you first run this script it can take a long time. When you run this script again it will only download the most recent data and so will complete much faster. I run this script once every few days to keep an up-to-date backup.

Raspberry Pi emonBase with RFM12Pi in Pibow Timber Case

If your not sure which way to go, its probably easiest to start with the Raspberry Pi oem_gateway forwarder to emoncms.org, you can re-configure it for local storage and backup via an external harddrive if you want later. If your more comfortable with Arduino code than the Raspberry Pi and linux then the NanodeRF (pre-assembled SMT) may be best for you.

Improving the thermal performance of buildings is an area where some of the largest energy and carbon savings can be made. Building energy use and carbon emissions can be reduced by as much as 60-80% through better insulation, draught proofing (improved thermal performance) and heating efficiency and controls. But how do you go about working out the performance of your house and what measures are best to undertake to reach this level of performance improvement? Improving building fabric is expensive, how do you work out which measures will be most cost-effective? and how do you make sure that your house actually achieves the target performance? how do you measure and check it?

These are the questions I’m currently grappling with for my own house and the openenergymonitor lab, these are also the questions we’re trying to develop improved processes for answering with our work with Carbon Coop.

Here’s a graphic from the Centre for Alternative Technology’s Zero Carbon Report illustrating the kind of performance improvements that are possible:

A few weeks ago I wrote a blog post about ethical and sustainable electronics.

In the post I mentioned a German project called Nager IT who have designed an optical USB mouse using low carbon materials and have gone to great lengths to source ethically produced components with a transparent supply chain and exploitation free manufacture.

We have decided to support the Nager IT project by becoming a UK reseller of their 'Faire Maus' or fair mouse. This mouse is as good as it gets at the moment in terms of ethical and sustainable electronics.

The mouse is a well-made three-button USB optical scroll wheel mouse made using low carbon materials, ethically produced components with a transparent supply chain and exploitation free manufacture.

The mouse is now available for purchase on a non profit basis (for us) in our shop: http://shop.openenergymonitor.com/fair-usb-optical-mouse/


The mice are assembled by hand in Germany and feel very well made, the texture of the wood plastic enclosure feels good in the hand and the sleek and rubbery USB cable runs smoothy over the table.

Every time I use the mouse it it reminds me that ethical and sustainable electronics is a goal which is worth pursuing.

Purchasing a fair mouse can be thought of like purchasing fair trade coffee; it might cost a little bit extra but you know that your doing good.
Checkout the great graphic Nager IT have produced illustrating their transparent supply chain behind this mouse.

Tweet-a-watt is a project from Ladyada / Adafruit to modify a Kill-A-Watt appliance power monitor to transmit the power data via Xbee to a computer (could be a Raspberry Pi) and post the value to twitter. Chris Whiting has modified the python code to post the data to emoncms



Chris Whiting writes: 

A Tweet-A-Watt is plugged into an outlet with a device plugged into it. A xbee is wired to the Kill-A-Watt electronics, which reads an analog voltage representing the power and current being used by the device plugged into the Kill-A-Watt. The xbee sends the data to a receiving xbee which is plugged into a computer using an USB FTDI TTL-232 cable.

I have a script called "wattcher.py" running on a Raspberry Pi which was originally developed by the folks at Adafruit. This script reads the data sent to the receiving xbee through the serial port. The script takes the raw data and processes the data to calculate the power being used. I modified the script to send the collected data to a web socket. The receiving web socket is the oem_gateway.py script that's running on my web server where Emoncms is currently installed.

Chris has kindly put his cod on GitHub for everyone to try: https://github.com/casestudies/tweetawatt

Since my last post introducing the emonTx V3  prototype design progress has been steady. The design has undergone several iterations and has now reached a stage of maturity.

The main features of the emonTx V3 have stayed the same:

• ATmega328 Arduino IDE compatible microcontroller
• RFM12B or Ciseco SRF 433/868/915Mhz RF wireless compatiable with RFM12Pi Raspberry Pi emoncms basestation
• 3 x Standard (23kW max) CT channels
• 1 x High sensitivity (4.5kW max) CT channel 
• Integrated AC-DC power supply to enable powering the unit from a single 9V AC adapter while also sampling the AC voltage to calculate Real Power and AC Vrms readings 
• Low power design with option to power from 3 x AA batteries for Apparent Power (current ony) measurement
• Enclosed in wall mountable extruded aluminium enclosure
• Terminal block connection for optical pulse sensor and DS18B20 temperature sensors
• Pre-assembled SMT electronics

emonTx V3 with 3 x AA battery's and 1 x CT (Apparent Power setup)

Fully assembled with antenna in wall-mount enclosure

I am currently in the process of obtaining assembly quotes from manufactures as well as performing lots of testing.

emonTx V3.1 PCB Design

emonTx V3.1 Schematic

The AC-DC circuit that was initially designed with the aid of simulation then bench tested is performing as expected.

Blue = output from 9V AC adapter Yellow = input to voltage regulator when unit is drawing 7.7mA  @ 3.3V, sudden dip is caused by RFM12B firing up to transmit four integer data packets (approx 24mA for 2.7ms)

If all goes well we're expecting to get the emonTx V3 into production in the next few of months.

Martin Roberts has developed a fantastic bit of firmware for the emonGLCD to enable it to be used as an RF scanner and signal strength meter on the 433 / 868 Mhz RF band.

 This makes the emonGLCD running this firmware a useful tool for debugging RF transmission and checking out signal strength. To run the firmware a small hardware modification is required to the emonGLCD to access the analogue signal strength output signal from the RFM12B.

Martin's sketch has been added to the emonGLCD github repo.

Full details including build-guide and discussion can be found on the original forum thread.