Monday, January 19, 2015
Monday, January 05, 2015
Connecting Arduino to NRF24L01 Boards
The diagram below shows how the NRF boards were connected for initial testing.
With this set-up, it has been possible to communicate between the boards from different locations in the house.
Learnt so far
- Getting the radios to work was easy.
- The Leonardo is not quite as simple to use as the pro-mini. Mainly due to the build in USB has to be handled by the Arduino software in a different way.
- Choosing the Leonardo for the transmitter will allow me to use all 12 analogue inputs.
- Just because a NRF24L01 board has a plug for an aerial does not mean that it is the high power version!
Friday, November 08, 2013
This is just some idle speculation on my part, and should not be considered as having any authority whatsoever.
Android to support alternative to Java
For some time, I have thought it must sit a little awkward with Google having Java so firmly entrenched in Android. Of course Google bought Android, so the original decision to use Java was not theirs, but have they considered moving away from it?
That would be a huge task. A number of things would need to be put in place before that could be considered. The development tools would have to be able to use the new language, and the runtime engine will have to be flexible enough to use the ne language as well as support the existing Java written apps.
Google have recently previewed a new IDE called Android Studio. Would this be better suited to supporting different languages?
With the recent introduction of Android 4.4, there is now the option to use an alternative runtime to Dalvik. ART. It would make sense to me that this would be an ideal opportunity to include the possibility of having an alternative programming language to Java.
As I said before, this is just speculation, but I really do wonder if by the time Android 5.0 comes out, will we be able to use something other than Java to write applications for android phones SDK? I know that is possible now with the NDK but that does not count!
Saturday, October 19, 2013
I have a PDF book that is a good reference. It would be great to be able to have it available on my tablet computer, but the PDF reader apps that have been tried are rubbish at navigating. Being a reference book, it is often required to skip to a specific chapter. This is slow when the PDF does not contain a sensible linked index. The only index it does have is in alphabetical order!
My initial thought was to use something like pdftk to split the book into separate files for each chapter. Having these in a folder, and using a file manager to select the required chapter as needed. This would work, but seems untidy. A better solution was required.
What I really wanted was to change the original PDF as little as possible. So I decided to add a single page to the start of the file with a linked list of the chapters. To do this required a little PostScript.
Create a file called, say,
index.ps. And in the file add some PostScript commands to create the index. First we can set a title. The word "Index" is placed near the top of a 4.5 x 6.5 inch page.
/Times-BoldItalic findfont 20 scalefont setfont 100 430 moveto (Index) show
Next the text for the chapters needs to be added.
/Helvetica findfont 12 scalefont setfont 20 400 moveto (Chapter 1) show 20 380 moveto (Chapter 2) show ...
The first line sets the font size, and then the next lines position and set the text. This is repeated as much as required.
Now we need to make the text clickable. This was done using pdfmarks.
[/Page 4 /View [/XYZ null null null] /Rect [8 393 52 413] /Subtype /Link /ANN pdfmark [/Page 5 /View [/XYZ null null null] /Rect [8 373 52 393] /Subtype /Link /ANN pdfmark ... showpage
The coordinates for each rectangle needs to align with the relevant text above, and the page number adjusted to point to the correct page in the PDF document for that chapter. This part was a bit long winded, and I am sure could have been made better with some more fancy PostScript tricks, but at least this works.
The Index was intended to go at the front of the PDF file so that it was the first page seen when the document is opened. If this was placed there directly, I would have to adjust the page numbers above by one to account for the extra page taken by the index itself. This would work, but caused an issue with the existing index in the PDF. This would also then be out by one page. So it was decided to put the index as the last page in the PDF. This way it would still be easy to find without disturbing the rest of the document.
The code to combine my new index with the existing PDF looks like this:
gs -dBATCH -dNOPAUSE \ -sDEVICE=pdfwrite \ -dDEVICEWIDTHPOINTS=324 \ -dDEVICEHEIGHTPOINTS=468 \ -dAutoRotatePages=/None \ -sOutputFile=temp.pdf \ MyBook.pdf -f index.ps
This adds the Index to the back of the PDF MyBook, and puts the result into temp.pdf.
The final stage was discovered by accident. I found that if I used pdftk to manipulate the book, it would update the internal links to keep them pointing to the correct page. So I could use pdftk to move the index to the front of my PDF as I first intended, and also, the existing index would also still point to the correct pages and not be shifted by one due to my added page.
The command I used with pdftk is as follows:
pdftk A=temp.pdf cat A228 A1-227 \ output MyBook_Index.pdf
I now have a quick index card at the front of my PDF book that can be used to navigate to the required chapter.
Saturday, May 11, 2013
First, it needs to be said. Automatic tracing and dumping data into Openstreetmap is not a good idea. This page is something I have been playing with as an aid to manual edits.
This is a simple summary of the steps I used. If you need more information, then you probably should not be doing this.
- Source Data
- Grab some data for the area of interest from Ordnance Survey.
- The Gimp
- Find the tile required and open in The Gimp. The following steps should isolate the buildings.
- Select by colour, threshold set to 26, pick the centre of a building, avoiding the antialiased edges.
- Sharpen selection.
- Fill whole selection with black
- Invert Selection
- Fill whole selection with white.
- Save image in bmp format.
- Make sure that you have the latest potrace that does geojson. With the required tif image from the OS data, run to following command:
potrace -b geojson -L XXXXXX -B YYYYYY -O 1 -a 0 tile.bmp
Replace XXXXXX and YYYYYY with the appropriate offsets for the tile being worked on. The required data is in the package downloaded from OS.
- Quantum GIS
- Create a new project with CRS OSGB 1936 / British National Grid. EPSG:27700.
- Load a new vector layer, select the json file from potrace and make sure the CRS is as above. Make sure that the scale is making sense. It would be possible to load another layer of known good data as a check. Be sure to allow on the fly CRS transforms if the data you check against is not OSGB 1936.
- Save the layer as a shapefile. Use the same CRS as the layer for the shapefile.
- The shapefile can now be loaded into JOSM. The polygons should line up well with the OS OpenData StreetView background images. However, there will still be a lot of manual cleaning up required. Extra nodes need to be deleted and squaring up done.
I am not sure if this actually makes much improvement over simply clicking over the background imagery by hand. Maybe someone else can improve this process a bit more. This is really written as a reminder to myself incase I come back to this later.
Thursday, February 21, 2013
Curiosity got the better of me. Having seen a few YouTube demos of the new Ubuntu touch interface on the phone, I was excited to learn that the developer preview was going to be released for the Nexus 10. Not that I am a developer though.
First thing I needed to do was decide that there was nothing on my tablet that I needed. Once I was happy about that, I went ahead and followed the instructions. The only problem I had was after unlocking the boot-loader the tablet would not boot up. It was stuck at the boot animation. As I needed to be in Android to complete the next step, I had to reinstall Android first.
After that little hiccup, it all went fine. Then I was presented with the image above.
There is still allot that does not work. Most of what does work, works well. There are many rough edges, and a few little quirks that no doubt will be adjusted over the next few months. The one thing that did strike me was the lack of a back button. That was probably the most unintuitive aspect to the interface.
It seemed that allot of what was working were internet apps. Gmail, Maps, Twitter, Facebook etc. And they all thought they were running on an iPad.
So far it seems like a good effort. Not sure I fully grasp the point though. It seems to be trying to do what Android does, but differently. What I was hoping for was something more like the Ubuntu Desktop. For that I would need at least a terminal, ssh, vim, LaTeX, apt-get etc. If proper user access control is implemented, that could be a real advantage.
In the meantime, I will be running Android on my tablet, as I only have the one. It would be nice to have a spare that I could keep on Ubuntu so that the development can be tracked. In a few months time, it may be worth trying again.
It is going to be interesting to see where this goes.
Monday, October 29, 2012
I have played around with this before. Having recently set up Mapnik again to render Openstreetmap data. Currently it is using the standard Openstreetmap osm.xml file so should look like the mad used on the main website.
This animation is created by rendering each frame with Mapnik. The script is based on a hack of the standard generate_image.py script that comes with Mapnik. It simply loops, and for each loop a new bounds is calculated to provide the zoom effect.
The next step is to make an animation based on a GPX file. That will take a GPX file as input and provide a zooming animation that shows the start, and an overview of the whole GPX track.