How to use a relay shield probably in the project?

As is know to all, if connect a LED to the digital output of Arduino, and make this pin output High or Low, the LED would be on/off. This is the first step to learn Arduino. But sometimes, we want to control some modules that works in high voltage/large current, for example, I want to control my lamp (works in voltage>100V) with the Arduino, it is not a good idea to connect the lamp to the Arduino digital output pin now.

Yes, the Arduino can only output voltage 5V max, and current 20mA max. It is much lower that the voltage that the lamp works with. We need a module to make it possible to control the high voltage/large current with Arduino. That is what a relay shield can do. The relay is an electrically operated switch, it acts like a soldier, accept low voltage signal commands for Arduino, and then control the high voltage gun on/off.

But it is theoretical, we need to notice something in actual usage. The Elecrow Relay Shield has the following points to ensure its usage. A reliable relays is the most important, and as the copper width and weight will Impacts the max current that can be flowed in the circuit, the width of the layout should meet the current requirements. Isolation within HIHG voltage and Low voltage circuit.

When the onboard 4 relays are all active, they need a max current of about 300mA, that is a large load for Arduino power circuit, especially when powered by USB. So, an extra power circuit is added in the elecrow relay shield, with a diode (D6) to protect the board when power reversed connected.

How to use a relay shield correctly? Cut off the power wire of your lamp; Connect on end to the COM1, and the other end to NO1; Ensure the manual control switch on the off side; Insert the relay shield on Arduino and power up. Now, you can control the lamp on/off by Arduino, digital out HIHG on D5 would makes the COM port connected with the NO1, that is , the lamp will be on; while output a logical LOW while makes the lamp off.

Beside a relay shield, there are also some other modules have many functions to make some project to better serve our life. For example, you can use a pressure sensor to make a system to test the air pressure or other pressure in your house. In a word, make full of some electronic modules to create some project to make your life more intelligent.