[NTLK] Power Adapter Developer's Guide

[Jake Bordens]

Hi folks.  Are there any “real” electrical engineers out there that would be willing to chat with me on Slack about the N2 Power Adapter Guide?  (I’m just a hobbiest maker at best)

http://www.unna.org/unna/apple/documentation/n2platform/n2-padg.pdf

Specifically, I’m exploring the ability of some pins on this port to accept a charger input.  I’m exploring the idea of whether a board could be made that provides a USB-C port that can both provide a standard serial port as well as charge the Newton.   USB-C can provide 9v 3a, and that can be regulated down the 7.5v needed by the Newton.

I’ve played with it a little bit so far, but I don’t have a good way to test that this input is working properly and not in fact doing damage or overcharging the battery.  I had hoped when power was applied to this port, the newton would show “charging” in the battery meter, but it doesn’t see to do that.  Either it doesn’t work that way, or I’ve already damaged the port on my test newton ☺

Also they talk about using a 100k resistor to signal to the newton that there’s an charger present.  In a final design, I think you need more than just a resistor. Since unfusedPsVin provides battery voltage with no adapter is present, putting a 100k across to PsAdaptIn when no power is present seems wrong to me, as the battery voltage could trigger the PsAdaptIn signal when no adapter is present.  I think you need a diode at the minimum such that when the power supply is disconnected, no voltage appears back to the PsAdaptIn pin from unfusedPsVin.

It anyone has any idea on how this might work, how to test safely without destroying a Newton, let me know.