[NTLK] Power Adapter Developer's Guide

[Jake Bordens]

> Cool. I am quite unsure if there is any provision to protect the batteries. I read the documentation and 
> understood that the pin directly connects to the power system, no fuses or anything. So the question is, 
> is there charging electronics between the 7V line and the battery, or instead between the power pin and 
> the battery. Not sure how, but it should be possible to measure if there is a mosfet or any such thing 
> between the battery and the internal connector.

This is my concern.  "Unfused" makes you think it is a direct connection between the battery terminal and the "unfusedVin" pins on the internal connector. Checking with my meter, you don't get direct continuity, though you do get a short beep which usually indicates there are some capacitors between the battery terminal and the "unfusedVin" pins.  Perhaps there are mosfets in between..  I ordered some connectors so that I can build a voltage/current monitor and put it between the OEM power supply and the Newton to see how it behaves during charging.  Then I can compare the behavior of the internal port.

For the internal charger, my current circuit involves two diodes and the 1k resistor.  Really you need only one diode to prevent the battery voltage from triggering the sense pin. (I did verify that a 1k resistor between sense and unfusedVin while on battery does make the newton think there is an adapter installed, so a diode is necessary)  However, I'm using 2 diodes as to keep the voltage drop somewhat the same between the sense pin and the batteryVin pin.  I'm not sure what the Newton uses the voltage on the sense pin for, but the docs indicate it should be the same as the battery voltage.