Commonly used current -based circuit NE555. It is an integrated circuit with a wide range of purposes, such as forming timer circuits, comparator circuits, delayed switch circuits, etc. TDA2822, an integrated circuit. This is a low -voltage and voltage adaptation range with wide power audio amplifier circuit. Use stereo sounds, handheld -holding loudspeers and other occasions. Four luck calculated amplifiers LM324. Contains 4 sets of the same independent computing amplifier circuit. It can form a comparative circuit, frequency division circuit, and front amplifier circuit. Logical digital circuit CD4017. It is a decimal decoder integrated circuit, which is used for decoding, counting, time, etc. in digital logic circuits.