学习ext+direct的tree源码，功能完全，代码完整，对初学者有用-The tree learning ext+ direct source, fully functional, code complete, useful for beginners

Gallium Arsenide Diode Infrared Source Optically Coupled to a Silicon npn Phototransistor
High Direct-Current Transfer Ratio
Base Lead Provided for Conventional Transistor Biasing
High-Voltage Electrical Isolation . . . 1.5-kV, or