About the working principle of single touch mode light switch

Working principle of single touch mode light switch

The touch mode light switch introduced here only uses one touch electrode to turn the lights on and off. Like the touch mode light switch, it uses a two-wire system with phase wires entering the switch, which can directly replace ordinary switches without changing the original indoor wiring.

working principle

The touch switch circuit is as shown in the figure. The right part of the dotted line in the figure is the ordinary power supply wiring, and the left part is the touch light switch circuit. The main loop of the switch is composed of VDl-VD4 and VS. The integrated block A and other components form the control loop of the switch. R51, VD5 and C3 form a simple resistor step-down voltage stabilizing circuit, which outputs about 12V DC power for the control loop and other power. LED is a low-light indicator, used to indicate the position of the touch switch at night, which is convenient for use. If low-light indication is not required, use wires to short-circuit the positive and negative pin solder joints of the LED. Integrated circuit A is a double-D flip-flop, which is connected into a monostable circuit and a bistable circuit. The function of the monostable circuit is to perform pulse broadening and shaping of the touch signal to ensure that each touch action is reliable. The bistable circuit is used to drive the thyristor VS on or off. M is the touch electrode piece. If you touch M with your finger, the voltage drop of the alternating current leaked from the human body on the resistor R2 will enter pin 3 of A, which is the CP terminal of the monostable circuit, causing the monostable circuit to flip into a transient state. , its output terminal Q, or pin 1, jumps from the original low level to a high level. This high level charges Cl through R3, causing the potential of pin 4, or terminal R, to rise. When it rises to the reset level, the monostable state The circuit is reset and pin 1 returns to low level. Therefore, every time the electrode pad M is touched, pin 1 outputs a positive pulse with a fixed width. This positive pulse will be directly added to pin 11, which is the CP terminal of the bistable circuit, causing the bistable circuit to flip once, and the level of its output terminal Q, or pin 13, will change once. When pin 13 is at high level, the gate of VS receives a positive trigger current through R4 and is turned on, that is, the electronic switch is closed and the lamp lights up. At this time, the voltage across capacitor C3 will drop to about 3V, and the light-emitting tube LED will go out, but A can still work normally. When pin 13 outputs low level, VS loses the trigger current. When the alternating current crosses zero, it turns off and the light goes out. At this time, the voltage at both ends of C3 can return to 12V, and the LED lights up for weak light indication. It can be seen that every time the electrode sheet M is touched, the action of "turning on" or "turning off" the light can be achieved. Component selection and production A uses a CD4013 double D flip-flop digital integrated circuit, which is packaged in a 14-pin dual in-line plastic package. VS uses small plastic packaged unidirectional thyristors such as MCRl00-8 2N6565 type. VD1-4 uses silicon rectifier diodes such as 1N4004-1N4007, and VD5 uses 12V, 1/2W Zener diodes, such as 2CW60 type. LEDs can be red light-emitting diodes.

It is best to use RJ-1W metal film resistors for R5, and RTX-l/8W carbon film resistors for the rest of the resistors. CT4 type monolithic capacitors can be used for C1 and C2, and CDll-16V type electrolytic capacitors can be used for C3. The switch housing is made of 86 series switch panels. In order to ensure the absolute safety of the user, a 2M high-impedance resistor can be connected in series between the touch electrode piece and the resistor R1. This switch is connected to the lighting circuit. The connection method is the same as that of an ordinary switch. , as shown in the figure, the phase line enters the switch. If the position of the phase neutral line is reversed, the circuit will not work properly. There is no need to debug the circuit after it is installed, it will work normally after power is supplied. Touch M once and the light will be on; touch - again and the light will go out.