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The closing door reminder circuit (1)

2014-11-06 10:19  
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The closing door reminder circuit (1)
See as in Figure 13-1, the circuit consists of a trigger relay circuit and an integrated music circuit. When the fridge door is open, the touch switch (K) is linked to the power supply, as the voltage on the terminal of C1 can not be changed suddenly, on the trigger terminal 2-pin of 555, there is a positive peak voltage(>2/3VDD) trigger which can reset the circuit, and the 3-pin is in low LEV, so VT1 is blocked. The capacitor of C1 charges with R1 and RP1, when the voltage on the 6-pin is 1/3 VDD lower than trigger voltage, 555 will be posited and the 3-lead is in high LEV, then VT1 is conducting and IC2 gets power and make sounds to remind the master of opening the door. Figure 13-1 The closing door reminder circuit (1)