Circuit Diagram:
When switch S1 is pressed momentarily, transistor T1 conducts to bring reset pin 4 of 555 to logic ‘high’. As a result, IC1 is activated and the alarm starts to sound. Simultaneously, the LED inside opto-coupler glows and the phototransistor conducts. As a result, trigger transistor T1 gets base bias via phototransistor and resistor R6. The alarm sounds continuously until reset switch S2 is pressed. When switch S2 is pressed, transistor T1 is switched ‘off’ to bring pin 4 of IC1 to logic ‘low’ and the alarm is disabled.
Source : Circuits-Projects
No comments:
Post a Comment