Here are simple diagrams for various applications to help your understanding.

[PLC ]

• PLC application using  RS-485 communication card [Download]

[Embedded system]

• Embedded  system application by TTL communication  [Download]

[PC Control]

• PC connection by IR-USB01 PC USB interface [Download]
• PC connection by RS-485 communication card  [Download]

[Arduino]

• Arduino connection by RS-485 communication  [Download]
• Arduino connection by PWM communication  [Download]
• Arduino connection by IR-STS01 Arduino Servo Tester Shield [Download]

[Raspberry Pi]

• Raspberry Pi connection by IR-STS02 Raspberry Pi HAT(Hardware Attached on Top)   [Download]

[Radio Control]

• Radio Control application by PWM  [Download]