Digital Input/Output DIO
A digital signal is a signal that exists in one of two states: high or low, open or closed, on or off. A digital input/output (DIO) device is hardware that sends or receives these digital signals. DIO devices are usually built around simple relays such as reed relays. These relays are normally open but close when power is sent to them. When the relay closes, it sends a signal that communicates a message or triggers another device.
Built around simple relays