2 PCS Electronic Accessories: 1 x 817 Optocoupler 4 Channel Voltage Isolation Board & 1 x Battery Undervoltage Control 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. Material:PCB attery Undervoltage Control Board: Type: Electronic products Model Number: 12V Charging Controller Protection Board Application: Computer Operating Temperature: -40-+85 Supply Voltage: 12V Electronic products: For Arduino STM Colour:Blue Size:40x29mm 817 Optocoupler 4 Channel Voltage Isolation Board: Colour:Green Size:48x42x38mm Package Contents: 1 x 817 Optocoupler 4 Channel Voltage Isolation Board 1 x Battery Undervoltage Control Board