The self-locking tact switch is a kind of passive components and cannot be used alone. It can only be used with active components to form a set of control system, and its function can be brought into full play. The working principle of the normally open tact switch: press the switch button to turn on the switch when it is working, and the switch is off when the button is released, and its internal structure is realized by the force of the metal shrapnel. The principle of normally closed tact switch: Press the switch button to turn off the switch while working, and the switch is turned on when you release your hand.

How does the self-locking tact switch work？

(1) When the power is turned on, when C9 is charging, the base and emitter of transistor Q1 are connected to the positive electrode of the battery power supply, Q1 is turned off, and the base of transistor Q2 is turned on to ground and Q2 is also cut off, so the circuit is cut off. , VCC 0V.

(2) When the touch switch is pressed, C9 discharges and C10 charges. Since the capacitor voltage of C9 does not change immediately, the base voltage of Q2 immediately becomes the capacitor voltage of C9. In other words, Q2 quickly saturates and ignites, while C9 discharges through R18. Set the collector voltage of Q2 to a saturation voltage of 0.3V. At this time, the voltage of the capacitor C9 is also 0.3V, and the voltage of the capacitor C10 is also 0.7V. The battery power is distributed in series through R16 and R17, where Q1 is saturated and turned on, so the circuit is turned on. When turned on, VCC is approximately the battery supply voltage.

(3) When the touch switch is pressed again, C9 is 0.3V and C10 is 0.7V, so C9 is charged and C10 is discharged, so the node of Q2 is reverse biased and the battery is on time. It charges C9 to R18 and is based on Q1. The pole voltage increases, Q1 turns off, the circuit turns off, and VCC becomes 0V.