Reading an SDHC card.

I've started working on the code to read a SDHC card. I've limited myself to ONLY reading SanDisk SDHC cards (4GB, 8GB, 16GB, 32GB) with FAT32 format. This should make the code shorter.

So far I am able to read the directory and the first sector of data from the first file. Luckily for this project I only need READ from the card. Writing files is much harder.

Bean

Sanity Check

Just as a sanity check I wanted to see how many characters I could put on a very small TV and still have the text be readable.

First I tried 32 characters per line, but that really is not enough and makes reading difficult. So I tried 64 characters, that was unreadably small on a 5 inch tube TV.

So I settled on 48 characters per line.

First I tried 24 lines, but the text was so close together that I couldn't find the start of the next line while reading. So I kept the text the same size, but put a 1/2 character space between each line. That looked good.

So I ended up with 16 lines of 48 characters. Then I make the line smoothly scroll up the screen. I still occasionally got lost finding the next line, so I put a gray bar across the screen after every three lines. Works perfectly. I never get lost now.

Oh, and the display is bitmapped. So it would be possible to show black & white graphics. The resolution is 384 x 192. That could in handy for science books and stuff.

Well, that wraps up the display part.

PropBasic Video Test Source Code

Bean

Welcome

I created this blog to discuss the development of a ultra low cost computer for developing nations. The name is taken from the saying "A rising tide lifts all boats". Hopefully a device can be created that will benefit everybody all over the world.

I'm talking about something that costs about $20. It will be completely open-source: Hardware, software and content.

A good portion of people in developing nations have access to a TV set (about 25% from what I read). So a TV will be the display device.

I am very familiar with the Parallax Propeller processor. So the Propeller will be the core CPU.

SD cards are really cheap and offer large amounts of storage (I'm thinking free books). So SD card will be the storage media.

Initially I'm thinking it will function like an eBook. And maybe some educational games so a 5 button (direction and ENTER/FIRE) will be on the device itself.

As for power, if the TV doesn't have power this device will not be usable anyway. So the power jack will be USB. I'm sure there are plenty of plug-in USB power adapter available all over the world.

A PS/2 keyboard connector and maybe a PS/2 mouse connector (I'm torn on the mouse).

Comments welcome. I'm I crazy ? I'm I off-base ?

More later...