Our little devices require a power. Mostly 5V DC. How to deliver it? The power grid is 230V so it is too much 🙂 and additionally, it is AC.
What can we do?
We can use a phone charger. It is easily affordable and does its job. But it looks bad and often we have power so close that it is a waste to use something with a long cord. We want to have a nice, small and compact device. What can we do?
To control 230V/110V devices we mostly use a relay module. What is a relay? We may describe it as a button but instead of a mechanical switch, we have an electric switch. Bluntly speaking it has 230V switchable by 5V. This describe any relay but what about a module?
The module gives us better protection, a control circuit and a device circuit has galvanic separation, often a led to show status and nice mount points. And such module can have more that one channel, it is a group of relays nicely mounted on a single board.