hi,

I have done such prototype:



I was used AT89S8252 and Dallas/Maxim DS1921 1-Wire Thermochron iButton. It provides RTC + thermosensor with litium cell inside. Maybe it has not good time accuracy, but I use it in a car and it works good with all features I have implemented by program: time, calendar, temperature, alarm, timer and digital bright control.

Regards,
Oleg