2 PCS Electronic Accessories:1 x 817 Optocoupler 4 Channel Voltage Isolation Board & 1 x Resistor 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. 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 Resistor Board: This is the "resistor replacement box", a low cost alternative solution, you can set flexible and fast resistor between 1R and 9999999R, 1R step precision. For educational experiments, electronic engineering design or test clipping are great applications. Design based on the resistor series theorem. 1/2 watt tolerance +/- 1% SMD resistors. High quality FR4 fiberglass PCB. Maximum operating voltage: 200V size: 90 x 35 x 10mm 817 Optocoupler 4 Channel Voltage Isolation Board: Size:48x42x38mm Package Contents: 1 x 817 Optocoupler 4 Channel Voltage Isolation Board 1 x Resistor Board