All electronic chips (in this example the optocouplers) have legs. These legs are numbered but the numbers are rarely written on the chip. To identify the leg numbers follow a simple procedure: looking at the chip you will see a small dot that indicates leg number one (1). Once you have located leg 1 it is easy to know the other leg numbers by counting up as you move to the adjacent legs and then around the chip to the other side.

Understand better the basic of electronics
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