Single-button 555 bistable switch design

Using the common 555 time-based integrated circuit as a bistable switch has the advantages of simple circuit, reliable operation and large output current. It can directly drive relay-type loads and realize the on and off control of the load with a light touch key.

The circuit is shown in Figure 1 (click to download the schematic diagram). When the circuit is just powered on, the presence of C1 makes the IC (555) pin ⑥ obtain a positive pulse, and its pin ③ outputs a low level. At this time, there is no voltage on C2. Press the light touch key S, and the "0" level on C2 acts on the IC's pin ②, and the pin ③ flips to a high level, charging C2 through R3. After S is released, C2 is charged to Vcc, and the IC's pins ② and ⑥ are biased to 1/2Vcc by R1 and R2, and the high level state of pin ③ remains unchanged. Press S again, the voltage on C2 makes the IC pin ⑥ voltage greater than 2/3Vcc, and pin ③ flips to a low level again. After S is released, the voltage on C2 is discharged through R3 and IC pin ③, and the voltage of pins ② and ⑥ is still 1/2Vcc, and the low level state of pin ③ can be maintained unchanged. It can be seen that each time S is pressed, the high and low levels of IC pin ③ change once.
As long as the time of each key press does not exceed 1 second, this bistable switch can normally realize the high and low level change of IC pin ③. However, if S is pressed and held, the high and low levels of IC pin ③ will continue to change.