Carl's Blog

Previously

So I left the last article with the following:

Well apart from the hardware I need, so issues need to be addressed which may or may not require extra hardware – as I’ve just thought of them.

• DateTime equivalent object for when I register a pulse
• Work out how long these will last on battery
• Can I set an interrupt to go off when a digital value hits a threshold? Or does this require analogue input? If I can it would massively save on battery as no polling! But, it may require fiddly per-house calibration, which the brute force method ignores
• Laser/3d Printed box and some form of mounting which will let me attach to anything. Probably going to be velcro

So I’ll go through what has been done since then via this criterea.

Hardware Changes

The DateTime object style thing was achieved through an RTC module (http://www.sparkfun.com/products/99) which communicated to the ‘duino using the I2C bus and takes 5V. A microSD card shield was also added to the hardware for saving events into a simple text file (http://www.sparkfun.com/products/9802).

Rather than use my hastily build photosensor, I used a load of RFXcom sensors as they are well built and have a housing designed for sticking to the meter (Which is by far the biggest engineering challenge of this project). A board layout for interfacing with the sensor units was created and the gEDA/gSchem schematic file can be found on the git hub project page.

Software Changes

Well, apart from the stuff which interfaces with the RTC module and the microSD card, not much has changed code wise. The way the RFXcom modules work was backwards to my prototype, so I measured the time it takes to discharge a capacitor rather than charge. An LED on a meter normally flashes for .1s, so the timout is set to 0.05s.

Battery Life

Using a multimeter showed the whole sensor drew 92mA. It isn’t ideal, but with a 6 AA battery pack which packs ~3000mAH which lasts a bout a day ( ) However,  that was with a ridiculously high powered infrared LED on the RFXcom board. Using just the photosensor (rather than the reflective) the power output was 42mA and that was with the SD card always powered. There is a lot of scope for battery life improvement on this project.

Source

The source can be found on my github page at https://github.com/carl-ellis/Arduino-Gas-Sensor .

September time is conference time it seems and I am currently at UbiComp2010. The UCSE2010 workshop convened yesterday which was very successful and discussion driven.

One of the main technical company sponsor was in the workshop, Autodesk, and gave an interesting talk on how they are opening their whole building’s Building Information Model(BIM) to the internet. I would point you to Digital 210 King for more information.

2 weeks ago I was at IPIN, which was hosted for the first time at ETH Zurick. Very successful conference, with lots of content (200+ talks!).

For all those interested, I am putting my slides on slideshare, those being my IPIN talk (30 min ish) and my UCSE talk (5 min). The UCSE presentation has had a slide removed for confidentiality reasons, so the short presentation is even shorter.

Please navigate to http://www.slideshare.net/CarlEllis to view.

C

Woo,

I am now an officially funded Ph.D student soon to be studying Localisation of mobile nodes in Wireless Sensor Networks.

I will now eat cake.