Here’s a proposition for a Gadgeteer module (yes, I know 
)
Quick features :
- type “I” module
- 256K I2C eeprom
- selectable I2C address via dip-switches
- can be chained to other I2C Gadgeteer modules or standalone devices (LCD, other eeprom for example)
- exposed 3.3V, 5V, GND, SDA & SCL pins via non populated PTH headers or populated screw-terminals
- selectable I2C pull-up resistors via dip-switches
- routing of the Gadgeteer socket’s pins 3 & 6
Details :
For my project, I needed some storage capabilities. I could have used SDCard, which is what I’ve done so far, but it has some drawback : it needs some more
libraries, which eats up memory on the Panda boards.
Since I have an I2C LCD in the project, I thought it would be wiser to also use the I2C line for storage, hence the choice of I2C eeprom. This will save some precious
memory space, I think. And while I was at it, I thought I could build a Gadgeteer module for it but with non-Gadgeteer compatibility also in mind.
About the eeprom chip, I’ve chosen a DIP package because I personnaly have this one and some MSOP-8. But those are really small (3 mm, 0.118"). And
I don’t have the package in Eagle for them. Also, DIP format is far easier to solder and generally easily available.
Unlike many (all ?) existing type “I” modules, this one has 2 Gadgeteer headers so that other I2C modules can be chained. To me, only one header defeats the purpose
of I2C and is not a good idea.
Since this is I2C, I’ve also exposed the SDA/SCL lines to the non-Gadgeteer world by using PTH header and/or screw-terminals. This also permits the use of this module on non-Gadgeteer boards.
In the same spirit, the power/ground lines are of course also exposed. Again, PTH header or screw-terminal can be used.
The dip-switches permits the inclusion of pull-up resistors on the I2C lines. This can be very useful if using Gadgeteer software I2C for which pull-up are mandatory on
modules, which is of course almost never the case.
Also, since this is a type “I” module, it should also provide connectivity for pins 3 & 6. This module does not use them, so they will be routed between the two Gadgeteer
connectors. Here again, two dip-switches are used for this. In the “OFF” position, pins are not routed and are not available at the “out” connector. Obviously, in the "ON"
position, pins 3&6 will be available.
This can be very handy if you use a type “I” module that is using pin 3 (for example) and another one that is using pin 6 (in addition to I2C pins) : you put this eeprom module
between the 2 and put the switch “pin 3” to OFF and “pin 6” to ON.
What do you think ?
ps: I have one question for specialists : do I need ground planes, here ?