* I-Button reader (for ButtonImmobilizer)

* CourtesyLightController (dimming interior light after you leave..)

* RealTimeClock (nice to have real-time for datalogs)

* possibly other functions (???)

Can be bundled on a low power consumption board (that needs to be on all the time).

There is a good chance that RadioBoard (under desing now) will provide the hardware necessary for these function as well.

There must be some atmega just right for the job:

..... write your thoughts here ....

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Atmel has a small board called the butterfly. It has an LCD display and is inexpensive. It would be just the thing for a dashboard display to give time, WB02 display etc.

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Actually AtMega128 could be used (think semipopulated AfreshBoard)spending much time in sleepmode, if the other components are careful not to consume much current.

Suggestion: 8 MHz Atmega128L, driven at 4 MHz, mostly sleeping, making his own 3..5 V from the battery with SW-driven switching regulation.

You need a PNP (from VBatt), an NPN (driving the PNP), 2 base resistors, a BE resistor for PNP, an LC and a flyback diode for the switching regulator. Around 100Hz you have enough time to measure and switch the transistors.. Also a 5.1V Zener parallel with C in case you get the program wrong :-)

Note: The atmega ADC can be made to measure it's own supply voltage...

why not have the 5.1V Zener go to the base of a NPN and have the NPN Emitter going to reset. That way if you go over voltage the system is reset and the switching stops. So bad code would just loop.