WeMos D1 3v module relay shield at work main.

One of my project’s most used components is undoubtedly the relay; its working is quite simple; you can find It as a module or only the relay.

You can find multi-voltage relay modules on AliExpress

The only problem you can have is that relay needs some power to be activated, so It’s preferable to use a transistor like 2n3904.

You can find 2n3904 transitor on AliExpress

Here is a simple breadboard connection schema; as you can see, I use a microcontroller pin to activate a transistor that gets 3.3v power from the relative pin, but if you can, It’s better to use an external 3.3v.

Here is the breadboard with this simple circuit.

Now I’m going to create the PCB, and I add a set of male pins to manage with a jumper to select a specified WeMos pin. The options are from D5 to D8 and D0.