4 Channel Relay Board For Arduino 
One normally closed contact and one normally open contact 
Triode drive, increasing relay coil 
High impedance controller pin 
Pull-down circuit for the avoidance of malfunction 
Power supply indicator and Control indicator lamp 
Power supply and relay instructions, lit, the disconnect is off; 
The input signal, signal, common Terminal and start conducting; 
Useful for appliance control; 
DC or AC signal, control, you can control the 220V AC load; 
There is a normally open and one normally closed contact; 
The module is compliant with international safety standards, control, and load areas isolation trenches.