In this chapter, you learned how to use the GPIO pins as outputs to drive LEDs (GPIO inputs will be covered in Chapter 5, User Input, so stay tuned!). We used both the on-board LEDs, as well as external LEDs that we wired up ourselves. You learned about the current sourcing limitations of the BeagleBone's GPIO pins, as well as how to use an NPN transistor to source higher currents from them. You learned how to use Cloud9 to run Python programs that drive the LEDs, and how to run multiple programs simultaneously and automatically at startup.
In the next chapter, you will learn about pulse width modulation and the analog-to-digital converters.
