In this chapter, we went through a quick description of basic electrical engineering concepts as a foundation for interfacing the BeagleBone with other things. We looked at the available signals and power on the expansion connectors, P8 and P9, on the BeagleBone. We also briefly looked at the pin mux used to select different functionalities on the expansion connector. For the expansion connector, we discussed several details that are critical for interfacing. The BeagleBone uses 3.3V for all the logic signals. The only signals that aren't 3.3V on the BeagleBone are the 1.8V analog to digital converter inputs. We then looked at using a transistor to interface to signals that aren't 3.3V and to drive higher current.

We also looked at a few specific things that can be interfaced using a transistor. For the LEDs, we looked into determining the resistor values using Ohm's law. For relays, we touched on hazards such as inductive kickback, which can be suppressed with a diode.

Then, we turned...