[Arduino]2 Relay Module

 不錯的文章:

Interface Two Channel Relay Module with Arduino
https://lastminuteengineers.com/two-channel-relay-module-arduino-tutorial/

relay spec:
http://j5d2v7d7.stackpathcdn.com/wp-content/uploads/2015/10/SRD-05VDC-SL-C-Datasheet.pdf