Single-button bistable electronic switch made using NE555

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 realize the on-off control of the load with a light touch key.

When the circuit is just powered on, the presence of C1 causes IC (555) pin ⑥ to obtain a positive pulse, and its ③ pin 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 voltages of pins ② and ⑥ are still 1/2Vcc, and the low level 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 time of each key press does not exceed 1 second. But if you hold down S, the high and low levels of IC pin ③ will continue to change.