Obviously there are purely mechanical self-locking switches, why use so-called touch switches?

         My understanding is to avoid the "jitter" of purely mechanical switches. In the past, when doing digital circuit counter experiments, a mechanical touch switch was used to input pulses. The counter should be increased by one by pressing the switch, but by pressing the switch, the counter would have increased by dozens. , Several hundred, this is the "jitter" of traditional mechanical switches. This is one of them. It is also possible to consider that the contact resistance of the mechanical switch becomes larger after using the mechanical switch for a long time, which will affect the power supply of the circuit. After switching to the one-button switch, the weak current flows through the mechanical switch, and some contact resistance does not affect the circuit function. Can greatly extend the repair period of the product.
         Single key switch principle:
         The positive feedback coefficient is greater than the negative feedback coefficient, so that the circuit will not be unstable even if the switch is not pressed. Only when the switch is released and the voltage on the capacitor changes to a certain value and then the switch is pressed, the circuit will flip. The structures of Figure 1 and Figure 2 have certain power consumption. Figure 3 is the most suitable battery-powered device. The static power consumption of the CMOS circuit is basically zero.