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. If it is a pulse signal, please note that the limit of 817 is below 4KHZ. If the control signal is greater than 4KHZ, please do not use this module, it will not work properly. Colour:Green Material:PCB Size:48x42x38mm Package Contents: 2 x 817 Optocoupler 4 Channel Voltage Isolation Board. Only the above package content, other products are not included. Note: Light reflection 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.