4h timing circuit composed of 556

(1) Introduction to circuit principle As shown in Figure 3-9, it is a 4h timing circuit composed of a 556 pair base circuit. By connecting the N8281 frequency divider network to the 556 dual time base circuit , a considerable time delay can be obtained without using large capacitors. The first time base circuit of 556 works as an oscillator with a period of l/f. The output of the oscillator is connected to the N divider network to produce a signal output with a period of N/f, which is used to trigger the other half time base circuit. Connecting the frequency divider to the input terminal ⑧ of the second time base circuit determines the total amount of delay generated by the frequency divider. The delay time is 30min, with 4 levels including th, 2h, and 4h. If additional N8281 frequency dividers are connected in series , the total delay can be increased to days or even weeks.     (2) Component parameter selection. The component selection period is shown in Figure 3-9. There are no special requirements. (3) The 4h timing circuit     composed of 556 is shown in Figure 3-9.