This circuit can detect the illumination inside the refrigerator. The circuit is as shown in the figure. It is composed of 555.
555 and R2, R3, Cl form a forced multivibrator, and the forced reset end 4 is connected to the c pole of the photosensitive tube 3DU5. Under the bright illumination, the 3DU5 is turned on with low resistance, so that the 4 feet of the 555 are Low level, forced reset, the oscillator does not oscillate, the speaker does not sound, when there is no light, 3DU5 is cut off and high resistance, 4 feet is high, 555 oscillator starts, its oscillation frequency is f=1.44 ∕(R2+2R3)Cl, using the principle that the lamp is bright and vibrating can not support the grip, it can detect whether the illumination lamp in the refrigerator is extinguished after closing the door.
Silicone Rubber Keypads Membrane Switches
A Silicone Rubber Keypads Membrane Switch uses compression-molded silicone rubber with conductive carbon pills or with non-conductive rubber actuators. The compression molding process creates an angled web around a keypad center. When a keypad is pressed, the webbing collapses or deforms to produce a tactile response. When the pressure on the keypad is released, the webbing returns the keypad to its original position with positive feedback. The closure of the switch circuit occurs when the conductive pill or printed conductive ink makes contact to a PCB when the web has been deformed.
Silicone Rubber Keypads Membrane Switches,4 Buttons Membrane Switch,Production Equipment Membrane Switch,Digital Control Membrane Switch
Dongguan Nanhuang Industry Co., Ltd , https://www.soushine-nanhuang.com