“In this tutorial we will show you how to use a NodeMCU and a relay board that can be used to control things like solenoid valves.
We are going to use the readiness.io platform to observe a sensor (in this case a water level sensor) and if it is low, open our solenoid valve to let a tank fill up.
The board we have created is fairly generic and provides for two inputs - that could be from push buttons or level switches or some other type of switch. It also has two outputs that are connected to two relays. There is also a DC-DC power module that allows you to power the NodeMCU from an external power supply up to 25VDC and provides the output for the relay board.”