Friday, 19 September 2014

OLPA . Or a project long not done..

This hiatus has been a lot longer than I have hoped, but there's finally a new project at my desk. It's an OLPA (One Laptop/lunchbox Per Adult), named after the famous OLPC from some years back.

Ever since the OLPC project was announced I have wanted an homemade portable laptop/lunchbox type computer with OLPC like Screen, with black/white reflective reading for outdoors use. The same screen works as a regular color LCD when used indoors with the back light connected. Even thought this type of screen uses more power than E-paper,  it's  also is a lot faster to refresh so it's better suited to web surfing etc.

Currently I have tested the display, controller, Pi alongside wireless KB/Mouse and system is quite usable even though as fast as today's commercial laptops/tablets. Next part of the project will be making/purchasing suitable enclosure and installing these components to make basic system.

Picture of Reflective LCD screen
Reflective display + parts.
While deciding the enclosure there's also the aspect of making this portable computer system battery operating. I hope to get system running at least 3 to 5 hours on lithium battery, but 10 hours might be achievable without adding too much bulk or weight. Raspberry needs 5Volt feed and the screen+controller can run on almost anything between 5-24 Volts DC, so it would be quite easy to use one of those premade battery packs sold for laptop/phone users.

On future upgrades.. I allready have wifi -module that's supposed to be supported by Raspbian which I have not yet tested. Using wireless net will eat power, but on the other hand it eliminates the need for ethernet-cabling. Also alternative CPU board is under consideration. At the moment this system is based on Raspberry Pi, but Banana Pi looks like valid alternative since it offers overall better performance with less power use.

At the moment, there's not much point making any video of this. When(if?) I get this to packed and working ... perhaps.

Wednesday, 19 February 2014

A new scope.. Well... At least it's new for me.

Hi, this is an update of my long time project. I finally got myself an oscilloscope. Well, technically I have had a real old one for some years but finally I have a DSO. Rigol 1052, there at the left corner atop of my old Russian cathode ray tube scope.



And my electronics desk needs some cleanup, too.


Rigol 1052 is over 5 years old model, so it's nothing new nor fancy. But it works... mostly that is. I got a good discount on this one, since the long memory (1Meg) is partially broken. As you see at the picture, the second trace has nasty noise overlaid atop of probe calibration signal.  I took some time to test the scope and noticed that there must be something really odd at the digital part of the system. Analog front-end and AD converters work just fine and the problem appears only at one of two channels. (see picture)
Direct capture of Rigol screen.

When I got the scope, I even took some time/effort to open it up and look if there could be anything obviously wrong at the board. But as far I could see everything looked like it should be. So, I just closed it back up and keep it as it is. In theory there could be a cold joint or short right under Atmel FPGA, that causes bad data to be moved to external ram. But it's highly unlikely I could do anything to fix the board here. So it's better to use the scope as it is and not break it any further.


Not much to see here.



All in all, the good thing is that this error does not appear at all if the Rigol is set using short sample memory. So, even though this scope has some (non typical, I may add) issues, it's still quite usable for  the needs I have. And the price was right for me, so I can't (nor want) to complain.