As shown in the figure is a music-type refrigerator door reminder circuit. The circuit is composed of a buck rectifying and stabilizing circuit, a delay circuit, a music integrated circuit CIC2851E, a speaker and so on. The step-down rectifier and voltage-stabilizing circuit provides a DC voltage of about 3V for the entire circuit.
When the refrigerator door is opened, the switch AN is turned on, and the capacitor C3 is charged through R3. As the charging progresses, the base potential of BG1 rises. After a delay of about 20 minutes, the voltage on C3 turns BG1 on and BG2 ends. Correspondingly trigger the work of CIC2851E, the music signal output by BG3 is amplified, and the speaker Y is driven to send out the melody of "bell chimes ..." to remind the host to close the door quickly. If the door of the refrigerator is not closed, the music will keep coming. The length of the delay can be selected according to the time to access the food, generally between 5 to 15 seconds. This circuit takes 20 seconds.
The circuit requires that the voltage across the DW is about 3V. If it is too high, the integrated circuit is easily damaged. Resistor R6 is used to adjust the speed of music rhythm, and its value range is 20kΩ≤R6≤120kΩ.
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