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After a few comments regarding my code to read data from a Sensirion SHT1x with a Raspberry Pi, I’ve got some updated code.

Please see my previous post for general information, but use the code here.

The list of changes are:

• Added Dewpoint calculation from Page 9 of Datasheet
• Updated Humidity calculation Coefficients to recommended (12 bit) figures from Page 8 of Datasheet
• Updated Temperature calculation Coefficients to recommended (3.3 Volt Interpolated) figures from Page 9 of Datasheet

Any references to the datasheet refer to the Version 5, Dec 2011 datasheet found on Sensirions website.

Also note that the bcm2835 GPIO library has been updated and is now version 1.8 – Get the updated version from http://www.open.com.au/mikem/bcm2835/.
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Note: An updated version of my code is available at http://www.john.geek.nz/2012/11/update-reading-data-from-a-sensirion-sht1x-with-a-raspberry-pi/

The Sensirion SHT1x range of sensors provide a rather convenient way to accurately measure Temperature and Relative Humidity.

They aren’t the cheapest sensors as they typically sell for around $40, but they seem very accurate. I obtained a Sensirion SHT11 a while back as a free sample. I’d managed to get it working with an AVR ATMEGA328P for a planned project to build an Incubator, but now I wanted to read data from it using the GPIO of a Raspberry Pi.

I decided to keep the SHT11 allocated to my Incubator and bought an SHT15 for my weather station. The sensors are very similar. The data sheet shows that the SHT11 has an accuracy of ±3% Relative Humidity and ±0.4° Centigrade while the SHT15 is slightly better at ±2%RH and ±0.3°C. The communication interface is identical so no problems changing sensors in the future.

Before you can use my code sample, you’ll need to get the latest BCM2835 Raspberry Pi GPIO Library from http://www.open.com.au/mikem/bcm2835/ and wire up the sensor to the Raspberry Pi GPIO port.
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OK, OK. I admit it.

I’ve been very slack updating my blog recently. I’ve had a few overseas trips with work and been inundated with other work.

I promise I’ll update my site soon!

I’m off to Kiwicon V this coming weekend.

If you’re interested in computer security and haven’t got a ticket, I suggest you make some very last minute plans to get to Wellington for the 5th and 6th November.

My brother recently got married and as per the rules of engagement, the lead up to the event included a Stag night.

For my Stag night, I was given a hard hat complete with a flashing LED light and plastic antlers.

I decided I wanted to make something special for my brother. Something minimalistic, but effective.

The result was this…..
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This is a GlobalSat DG-100

It’s an amazing piece of Kit, but the software that comes with it is absolutely rubbish.

You can download all of the routes (and delete them from the unit) in one simple command with gpsbabel.

gpsbabel -t -i dg-100,erase -o gpx /dev/ttyUSB0 outputfile2.gpx

You’ll still need to set up the times/distance for recording for the switch positions A,B & C. I have mine set to 1,5 and 10 seconds. Easiest way to set these up is on a windows machine with DG Manager.

To combine two images of the same size with ImageMagick, you simply do the following:

The following will overlay overlay.png on top of output.png

mogrify -draw "image SrcOver 0,0 0,0 'overlay.png'" output.png

While this one will overlay overlay.png on top of input.png and save it as output.png

convert input.png -draw "image SrcOver 0,0 0,0 'overlay.png'" output.png

You can download imagemagick from http://www.imagemagick.org/

Selective colour replacement is easy from the command line with imagemagick.

You can download imagemagick from http://www.imagemagick.org/

The following will replace all red (#FF0000) pixels with blue (#0000FF)

convert sourceimage.png -fill "#FF0000" -opaque "#0000FF" destimage.png

I’ve been doing some performance tests on WordPress to see how much of a difference the WordPress Super Cache plugin made.

It turns out that the plugin makes a huge difference. (more…)