The power switch circuit is composed of double-D flip-flop CD4013 and resistance container. As shown in the figure, ICA and R1, C constitute a monostable trigger. (the monostable circuit has only one stable state, and it will return to the original stable state after a period of time.) ICB is composed of bistable flip flop (bistable circuit has two stable states, which will be maintained after flip flop. It has memory effect and is generally used as memory or counter).

CP is pulse input, R is reset off, s is set, q is output. When m is pressed, the rising edge of CP1 comes. Because D1 is always 1, Q1 is 1, which changes from low level to high level. At this time, Q1 charges C1 through R1. When the voltage on C1 reaches the reset end level of trigger, Q1 changes from high level to low level, and the conversion time is 0.7r1 * C. Since Q1 is connected with CP2, a pulse is generated at CP2, and since D is not connected with Q, Q will flip once for each pulse generated, so as to achieve the purpose of switching.

CD4013 switch application circuit

CMOS integrated CD4013 contact switch

The CMOS integrated circuit CD4013 has two D converters, which are connected into a monostable circuit and a bistable circuit respectively. The function of the monostable circuit is to shape the pulse width of the touch signal to ensure that each touch action is reliable. The bistable circuit is used to drive the transistor Q1 on or off, and then control the relay.

Here is the basic picture: it can be powered by 5V

CD4013 switch application circuit

M is the touch electrode. Touch m with your finger to make the voltage drop of the AC Leakage from human body on R4. The positive half cycle signal enters the third pin of IC1, that is, the CP end of the monostable circuit, which reverses the monostable circuit into instantaneous state. The output end Q, that is, pin 1, jumps from the original low potential to high potential. This high potential charges C2 through R1, which makes the potential of pin 4, that is, R1 end rise, when it rises to reset The monostable circuit is reset and 1 pin is restored to low potential. So every time I touch the electrode m, one pin will output a positive pulse with a fixed width. The positive pulse will be directly added to the CP terminal of the 11 pin bistable circuit, which reverses the bistable circuit once, and the potential of the output Q, which is 13 pin, will be changed once. When pin 13 is at high potential, the base of Q1 gets forward current through R2 and turns on, which makes the relay act and then controls it by its contact. It can be seen that every time the electrode m is touched, the relay can be “on” or “off”.

Component selection and production, CD4013 double D flip-flop digital integrated circuit, it uses 14 pin dual in-line plastic packaging. Q1 can use cs9013 or 2sc945 low power NPN transistor. The pin diagram and truth table of CD4013 are attached below:

CD4013 switch application circuit

CD4013 switch application circuit

matters needing attention:

I have found some problems in the actual production. I want to explain a few points to you

1. Try to get 5V power supply by reducing the voltage of the power supply through the transformer: when using the battery power supply, sometimes it can not be triggered, because when using the battery power supply, the circuit itself has no actual connection with the earth, resulting in that the AC Leakage from the human body to the earth is not connected with the earth of the circuit, so the voltage entering the touch point also decreases. In the practical application, it is found that the effect will be better if the metal objects are touched by hand.

2. The input resistance to ground R4 (2m) will also affect the sensitivity. If it is not sensitive enough, the 2m resistance can be increased, such as 2.7m.


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