Single button 555 bistable switch circuit

The common 555 time base integrated circuit is used as a bistable switch, which has the advantages of simple circuit, reliable action, and large output current. It can directly drive relay loads and control the on and off of the load with a light touch key. 　　See Figure 1 for the circuit

When the circuit is just powered on, the presence of C1 causes IC (555) pin 6 to obtain a positive pulse, and its pin 3 outputs a low level. At this time, there is no voltage on C2. Press the touch button S once, the "0" level on C2 acts on the ② pin of the IC, and the ③ pin flips to high level, charging C2 through R3. After S is released, C2 is charged to Vcc, while the ② and ⑥ pins of the IC are biased to 1/2Vcc by R1 and R2, and the high level state of ③ pin remains unchanged. Press S again, the voltage on C2 makes the voltage of IC pin ⑥ greater than 2/3Vcc, and pin ③ flips to low level again. After S is released, the voltage on C2 is discharged through R3 and IC pin ③. The voltage of pins ② and ⑥ is still 1/2Vcc, and the low level state of pin ③ can remain unchanged. It can be seen that every time S is pressed, the high and low levels of IC pin ③ change. This bistable switch can normally realize the high and low level conversion of IC pin ③ as long as the key pressing time does not exceed 1 second each time. But if you hold down S, the high and low levels of IC pin ③ will continue to change.