Design of an acoustic reporting circuit based on dual time base circuit design with too long opening time
When the door opening time of the refrigerator is too long, the circuit will automatically issue a report sound to remind the owner to close the door in time. The circuit is composed of a dual time base circuit 556 as its core, and its circuit is as shown.
The SB in the figure is a door linkage switch, and the door is automatically closed. When the illumination is lit, the circuit is also powered. The AC power is stepped down by C1 and R1. After the full-bridge rectifier QU is rectified and C2 filtered, the voltage is regulated to +9V, which is used as the supply voltage of VT1, IC1 and VT3.
VT4 is a photodiode, which forms a photoelectric switch with VT1, R3 and R4. The door is open and the light H is bright. VT4 is low-resistance (tens of KΩ) after being exposed to light, VT1 is positively biased and saturated, and its voltage between ce is lower than 0.4V, making the trigger end of IC1-a (1/2556) low, IC1 -a is set, the high level of the 5 pin output turns VT2 into saturation, and the low potential of the collector (about 0.3V) forces IC1-b to be in the reset state.
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