Basic timing circuit composed of 555

(1) Introduction to the circuit principle:
As shown in 3-4, it is a basic circuit composed of 555. If a trigger pulse as shown in Figure
3-4 is added to the ② pin of the 555 , its @ pin will output for a certain period of time. The interval pulses , with an interval T≈RC, are amplified by VT1 and drive the relevant circuit, such as the light-emitting diode LED in Figure 3-4.   (2) Component parameter selection . The selection of components is shown in Figure 3-4. There are no special requirements. (3) The basic timing circuit     composed of 555 is as shown in the figure