Nanode Applications Weekend and Gas Revisited - yet Again

As the Nanode project approaches the anniversary of its conception, and arguably just 4 months since birth, it was felt that it was time to get a few people together to talk about recent developments and applications.

The central London location of the Centre for Creative Collaborations (C4CC) was chosen as it is well equipped, easy to get to from Kings Cross and a good size - able to host between 30 or 40 delegates.

Saturday was well attended with about 30 present, and we covered a wide range of applications including energy monitoring, remote online bootloading of sketches, and recent developments with Pachube.

Glyn Hudson has done an excellent blog post about the event here - so there is no need to repeat in detail what he has covered.

The get-together brought many like minds into the forum, and it was not too long before we were discussing the use of open source hardware for wireless monitoring of electricity and gas consumption.

In the last few months Trystan Lea and Glyn Hudson of oem (openenergymonitor.org) have made huge progress on their open hardware energy monitoring system. They presented and demonstrated their open source energy monitoring system as an "end to end" solution - and this represents the first real, potentially commercial application for the Nanode as a web connectivity and data distribution device.

Glyn has developed a neat wireless sensor node, the EmonTx, based on Jeenodes and this is used as their electricity monitoring front end. The wireless packets are then sent to a Nanode fitted with a RFM12 transceiver board and thence up to the net.

Trystan has developed the server application including all the database, graphing and visualisation software. This application software is of exceptional quality and in my opinion exceeds that of some or most commercial energy monitoring packages. The point is however, it is open source, freely distributed and available for others to build upon.

So now we have the basis of a really good open source energy monitoring system - and its now time to start thinking about the "elephant in the room" - domestic gas consumption savings.

There are already a couple of commercial gas monitoring devices available - the Ewgegco does electricity, water and gas - hence the name, and the rather naff sounding Saveometer.

Conveniently Saveometer have provided this guide to compatible gas meters - so if you have one of these you are in luck.

The gas meter sensor uses a simple reed switch, activated by a small magnet fitted into the least significant dial. Reed switches create a fair bit of contact bounce, and tend not to work particularly well at very low currents (contacts need "wetting" current). So I have knocked up a very low power Hall sensor which I believe will be cheaper and more reliable in the long run.

Meeting ATEX requirements will be difficult, but I suspect that if I completely encapsulate the sensor in potting compound and meet the current and voltage limitations - then it will be fine from a technical point of view.

The EmonTx wireless sensor developed by openenergymonitor.org is based on the Jeenode circuit, but with additional analogue circuitry allowing the easy plugging in of current transformers, voltage sensors, pulse count sources and one wire temperature (or other) sensors.

As gas consumption and heating monitoring needs a pulse counter channel and temperature sensors, the EmonTx is readily adapted to this role. One proposal with EmonTx is to bring the four JeeNode ports out to external connectors - such that any sensor could be plugged into any port.

The use of a 4 pole 3.5mm jack connector would allow digital, anlogue, power and ground signal to be brought on each port. There are not many common sensors which could not be interfaced with this combination of signals, even if the sensor had its own tiny microcontroller onboard to create a serial data stream. This is the approach taken by Eric Ward with his "Half Bee" sensors which use an 8 pin PIC to provide a common emulated one wire interface for pulse counters, temperature sensors and 2 channel ADCs.

The 3.5mm jack is a compact connector and easily passed through walls, ceilings and flooring with an 9mm drilled hole.

Low cost, 5 metre pre-wired cable assemblies with a 4 pole 3.5mm jack are available here from Farnell.