GPIO pins are the most basic interface between a chip and the world. Configured as inputs they read whether a line is high or low, which is enough for a button, a reed switch, a motion detector’s output or an interrupt from another chip. As outputs they switch an LED, a relay driver or a transistor that powers a sensor only when needed. Most pins can also be reassigned to peripherals such as PWM, I2C or an ADC channel.
Their simplicity hides a few traps that matter in IoT designs. Pins source and sink only a few milliamps, so anything heavier needs a driver. Inputs left floating pick up noise unless a pull-up or pull-down resistor is set, and the state of GPIO during reset and deep sleep decides whether a connected load glitches on at the wrong moment.
Part of the IoT Glossary. Spotted an error or a missing term? Tell us.