>While the ESP8266 is often used as a ‘dumb’ Serial-to-WiFi bridge, it’s a very powerful microcontroller on its own. In this chapter, we’ll look at the non-Wi-Fi specific functions of the ESP8266.</p>
   <h3>Digital I/O</h3>
   <p>Just like a normal Arduino, the ESP8266 has digital input/output pins (I/O or GPIO, General Purpose Input/Output pins). As the name implies, they can be used as digital inputs to read a digital voltage, or as digital outputs to output either 0V (sink current) or 3.3V (sour