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 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 4KHZ, please do not use this module, it 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.