Digital inputs and dry contacts

Overview

A digital input (DI) has two states. It is used to connect reed switches, water and electricity meters, and pushbuttons.

Digital inputs fall into two categories:

• Voltage-sensing input (wet contact): for example, a controller Ax input. It detects whether voltage is present. Connect one contact of the button, reed switch or meter to a voltage source such as Vout, and the other to the digital input.
• Dry-contact input: controller W1/W2 inputs and WB-MR relay-module inputs, for example, detect whether the input is connected to ground. Connect one contact to GND and the other to the input. Open-collector outputs can also be connected by joining the grounds and connecting the output to the input.

An input connected to ground is on; an input not connected to ground is off.

“Dry” contacts are not electrically connected to other circuits in the external system: relay contacts, reed switches and mechanical switches are examples. An open-collector output is not itself a dry contact because it is not galvanically isolated from the external device.

Digital inputs on Wiren Board controllers

The Ax (D1) universal I/O channels can be used as digital inputs with voltages up to 40 V. Their signals are displayed in the controller web interface or transmitted over MQTT.

For input operation, turn off Ax_OUT (D1_OUT) on the Devices page. No other settings are required.

See connecting open-collector outputs and the WBE2-DI-DR-3 manual.