One Laptop Per Child Project

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(Basically a good idea but the OLPC seems to be going nowhere: this page kept as archive)

The Free42 website:

Click here to go to the Calc-42S wiki page on the OLPC website.

The OLPC home page:

RPN Free42 Operation, ongoing writing project (PDF)

Free42 skins for the OLPC

A set of skin files consists of an image file and an interface file.  
The image file is a gif, a pixel map.  It fits the display pixel for pixel.  If it has too many pixels it will more than fill the display and will be unusable.  If it has too few pixels it will appear too small and will not be easy to use.
The interface file has a .layout extension, but is a text file.  It tells Free42 where all the buttons are, where the display goes, what part of the button area moves when the button is "pressed", where the display annunciators are in the image, how much of the image to display and how much of it to avoid displaying, and so on.
For the OLPC, these two skin files need to reside in the following directory on your OLPC:


Free42.xo, latest build (Jan 27: 515,198 bytes)

click here to download 205k byte TAR file containing skins and benchmark program

Using the Linux TAR archive containing skins and benchmark program:
1.  Using the OLPC terminal, place the tar file in home/olpc/.sugar/default/Free42/data.
2.  While in this directory, type the following command: tar -xf skin_plus_benchmark.tar
3.  Now type the following command: ls
4.  You should see (among other things) 5 files:
     2 gifs, OLPC_42S_vt and hz
     2 layouts, OLPC_42S_vt and hz
     and one raw, Free42_benchmark
5.  Go to OLPC main screen and start Free42: you should now be able to use 2 OLPC skins.
6.  To import the benchmark program you will have to copy it to a non-hidden directory somewhere, since the "Import Program" menu does not yet allow you to go into the hidden directory tree .sugar where the file currently resides.

Individual files contained in TAR file above
These can be used also in windows and Linux versions of Free42:

Benchmark program for Free42 (PDF, 14K)

OLPC_42S_vt.gif (90K) Vertical orientation, default skin

OLPC_42S_vt.layout (2,183 bytes) Vertical orientation, default skin

PDF version of vertical layout file (3.4K)

Copy text from PDF, paste to notepad, save as OLPC_42S_vt.layout.

OLPC_42S_hz.gif (96K) horizontal orientation, optional skin

OLPC_42S_hz.layout (2,163 bytes) horizontal orientation, optional skin

PDF version of horizontal layout file (3.4K)

Copy text from PDF, paste to notepad, save as OLPC_42S_hz.layout.

Photo: HP-42S calculator emulator running on OLPC (JPG, 427k)

Photo: HP-42S calculator emulator on OLPC, daylight mode (JPG, 350k)

The OLPC vertical skin image is shown below. 
Area to the left of the calculator places the left edge of the calculator 50 pixels away from the left edge of the screen.  Areas to the right of the calculator are not visible to the OLPC user.  Annunciators visible here are used by Free42 and appear in the display area of the calculator when they are needed.  The OLPC user "presses" one of the keys on the calculator by placing the cursor (pointer) over the key and left-clicking.  When this happens, Free42 slightly repositions the image of the key itself to provide visual feedback: "the key has been pressed".  The number keys on the OLPC keyboard may also be used to enter numbers in calculations.  Other functions are also available on the OLPC keyboard.


This is an archive page, kept active for OLPC