THREE_MINUTE_TIMER

Published:2009/7/8 3:02:00 Author:May | From:SeekIC

When S1 is off, C1 charges to within 0.5 V of the battery voltage through diode D1 and resistor R4. When S1 is closed, the anode of the PUT rises to the positive supply voltage. The PUT does not conduct, because battery voltage appears in series with the charge stored on C1, which raises the gate of the PUT to a level positive with respect to the anode. The timer relies on the discharge of capacitor C1 through resistors R1, R2, R3,and R4. Once C1 is at zero volts, the PUT will turn on battery voltage to the Sonalert and cause it to sound.



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