Ed,

>    1) Each sensor has
>             - 1 temperature sensor
>             - 1 battery pack
>             - probably a diode?
>             - resistors?
>             - probably some microcontroller

A nW PIC (eg 12F675 because it has ADC) would be a good idea.
As you're wanting to run off battery, I'd SLEEP it, waking after a WDT
period (2.3s). Alternatively you could have the central logger wake the
sensor PICs, which would save power otherwise needed for WDT. If
the sensor PIC controls the sensor V+, consumption should be down in
the nA when no reading is being taken, making battery life very long

There are a few temperature sensors that would be suitable, eg the
good old LM35 or a one-wire Dallas. Have a look at their datasheets
for circuit suggestions

>    2) The central logger has:
>           - 1 PIC  (what type, I have the faintest idea,
>                     and if I should program it myself
>                     and whether it supports 3 or more
>                     sensors)

Any mid-sized PIC would do, an 18-pin 16F or 18F. Something a little
bigger (eg 16F873 or 18F2520) if you want to include an LCD. My
thought would be a two-wire connection to the remotes. Ground and a
wire that alternates as wake-up to the remote and for Manchester data
coming back

Any PIC(s) you don't have can be sampled free of charge

http://sample.microchip.com/

>           - USB or serial connector (female)
>           - something which can communicate to
>             the computer

Serial would be much much simpler. I don't know of any PIC that can
be a USB host, and USB is not worth the effort anyway when serial is
so easy. If you really have to have USB, then you'll need an interface
IC like the Vinculum

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