单键电子开关制作
原理图如下所示，基本原理是当按下按钮S1时。
555的引脚6,引脚2处于半高电平。当引脚3输出高电平时电容C1充电变成高电平，引脚3输出低电平时电容C1放电变成低电平。当按下按钮时引脚3,6的输入电压，电容C1的电压及输出引脚3的电平都会跟着变化。输出高电平时电容两端电压充到5V；当按下按钮时输出低，电容C1放电，电压为0V。当我们再按下按钮时又会输出高电平。三极管T1是用来驱动继电器的，当输出高电平时T1导通继电器接通。二极管在这里起保护作用。
Schematic for this circuit can be seen below. The circuit toggles a relay when button S1 is pressed. Operation of this circuit is simple. Pins 6 and 2 of 555 timer are at half power voltage. When output pin 3 is high then capacitor C1 is charged and when it's low capacitor is discharged. When button is pressed capacitor voltage appears on pin 6 and 2 and output pin 3 changes state as well as capacitor voltage changes. So when output is high capacitor has +5V. When we press the button pin 3 goes low and capacitor goes 0V, when we press button again output goes high again, so we have toggle functionality. When output is high transistor T1 is conducting current and relay is latched, when low relay is released. Diode D1 is used to protect transistor from back voltage generated when relay goes off.
A disadvantage of this circuit is that when we connect power to the circuit relay is engaged. A solution to this can be found on the second reference website below.
图 单键电子开关电路图(点击看原图)
