At the top is the isolated USB power switch to simulate unplugging and replugging the GSM modem. A relay is used to switch power, with the normally closed contacts used, so that power is not consumed by the relay (100 ma current draw) except in the short time the relay is actuated to remove power from the modem.
At the bottom is the basic sensor circuit. Two 10K NTC thermistors measure temperature, and with the accompanying 10 K resistors result in a variable voltage fed into AIN0 and AIN1 on the Beagleboard. A/C power presence is detected by the 'wall wart' on the left, feeding an isolator (the PS2501 quad opto isolator), which feeds AIN2 on the Beagleboard. It does not attempt to measure A/C voltage, but just determines if there is any. I was lazy when I designed it and had not figured out how to configure and read gpio bits yet, so I solved it by just measuring voltage.
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