School Bell Alarm

Description

School Bell Alarm Kits have a momentary switch. When the clerk presses it, the school bell rang according to the value of resistance and capacitance. This clock(timing) can be adjusted by changing the value of capacitor and resistance.

In the Kit Bell Alarm, we can change this ‘on’ time by changing the values of resistors and/or capacitors depending upon your requirement. The Microswitch (S1) is adjusted so that when the pen pressed the momentary switch. This press of the switch sends a logic low to the trigger pin2 of the LM555 IC which generates an active high output on pin 3. The IC is used in a mono-stable state. The value of the time for a high pulse on each trigger in the input is dependent on the value of the resistor and the capacitor. The output from the LM555 drives the ULN2803 IC (it acts as a current amplifier to meet the current requirement to drive the relay).

This Current Amplifier Circuit is an inverted IC means when the input is low output is high and vice versa. This IC LM555 drive the relay to activate the light which is a DC buzzer. The relay acts as an electromagnetic switch to switch the high voltage to activate the DC buzzer and activate the DC supply across the buzzer.