Introduction
As an electronics hacker, I'm always on the lookout for something nice to hack
and re-purpose for other things. Recently, I found that an online electronics
store here in the Netherlands had a 'digital keychain photo-viewer' on sale. While
other people may think that E10,- is too steep for a gimmick that you buy once and
then never use, my first thoughts were that E10,- is not a lot of money for a
LiIon or LiPo-cell, an 128x128 color display, a microcontroller, some flash and
an USB-cable. So I bought two.
If you're not interested in the nitty-gritty technical details, you can go directly
to the results.
When they arrived, I did what every self-respecting tinkerer does: take it apart. As expected, the device contains a cute 100mAh lil' LiIon or LiPo-cell, an LCD and a PCB with on one side the flash (an MX26LV160 2MByte flash-chip) and on the other sidean glob-topped chip. These chips have the die directly glued to the PCB and are covered with epoxy. This is a real cheap way to make PCBs, but it means there are no markings to go by. The ID of the chip had to be obtained by another means.
On the software side, the device acts like an unwritable mass-storage device filled with crap. Peeking on the software on the supplied CD (which offcourse was OSX and Windows-only) by using a debugger showed it wasn't supposed to: the device is read and written by writing commands to a certain offset into the mass storage device, and reading results and writing data by using other offsets. The debugger also revealed that the firmware identifies the chip by looking for SITRONIX CORP. at the start of the device. Some browsing at the Sitronix site revealed that the chip could only be an ST2205U. Luckily, the user manual for that is available on the 'Net: it seems that this chip is an 65C02 on steroids! Nice to find technology that was developed 26 years ago acting as the core of a toy I just purchased as new.
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