pullup resistors. When the switch is closed, it creates a direct connection to ground or VCC, but when the switch is open, the rest of the circuit would be lef

pullup resistors. When the switch is closed, it creates a direct connection to ground or VCC, but when the switch is open, the rest of the circuit would be left floating (i.e., it would have an indeterminate voltage). For a switch that connects to ground, a pull-up resistor ensures a well-defined voltage (i.e. VCC, or logical high) across the remainder of the circuit when the switch is open. Conversely, for a switch that connects to VCC, a pull-down resistor ensures a well-defined ground voltage (i.e. logical low) when the switch is open. https://en.m.wikipedia.org/wiki/Pull-up_resistor https://en.m.wikipedia.org/wiki/Pull-up_resistor