If it is a pulse signal, please note that the limit of 817 is below 4KHZ. If the control signal is 4KHZ, please do not use this module, it will not work properly. This relay module is 5V active low. Relay output maximum contact is AC250V 10A and DC30V 10A. Standard interface can be directly connected with microcontrollers. This kit is compatible for IDE, and STM32 Working status indicator lights are conducive for the use 4-channel relay interface board, which can be controlled directly by a wide range of microcontrollers such as AVR, PIC, ARM, PLC, etc. It is also to control various appliances and other equipments with large current. Widely used for all MCU control, industrial sector, PLC control, smart home control. Voltage Isolation Board Size:48x42x38mm Colour:blue/Green Material: PCB Relay Module Size: 76 x 56mm Package Contents: 1 x Relay Module 1 x 817 Optocoupler 4 Channel Voltage Isolation Board Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm. set2: 1 x Relay Module + 1 x 817 Optocoupler 4 Channel Voltage Isolation Board This module is used when the actual operation requires isolation control and voltage conversion. It can realize 3.3V or 5V to control the interface of 3.6--24V voltage level. After the control terminal is turned on, the controlled terminal will also be turned on. Photoelectric isolation has strong anti-interference ability. Can drive big behindPower triodes, MOS tubes, etc., where high voltage driving is required, can also directly drive low power 24V relays.