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Make a Refrigerator Door Alarm using 555 Timer IC and LDR - KT874

Make a Refrigerator Door Alarm using 555 Timer IC and LDR - KT874

SKU:KT874

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HARDWARE REQUIRED

PIN DESCRIPTION

555 TIMER IC

Pin

Name

Purpose

1

GND

Ground reference voltage, low level (0 V)

2

TRIG

The OUT pin goes high and a timing interval starts when this input falls below 1/2 of CTRL voltage (which is typically 1/3 Vcc, CTRL being 2/3 Vcc by default if CTRL is left open). In other words, OUT is high as long as the trigger low. Output of the timer totally depends upon the amplitude of the external trigger voltage applied to this pin.

3

OUT

This output is driven to approximately 1.7 V below +Vcc, or to GND.

4

RESET

A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides threshold.

5

CTRL

Provides “control” access to the internal voltage divider (by default, 2/3 Vcc).

6

THR

The timing (OUT high) interval ends when the voltage at threshold is greater than that at CTRL (2/3 Vcc if CTRL is open).

7

DIS

Open collector output which may discharge a capacitor between intervals. In phase with output.

8

Vcc

Positive supply voltage, which is usually between 3 and 15 V depending on the variation.

CAPACITOR

The Shorter Terminal is negative and the longer Terminal is Positive

CIRCUIT DIAGRAM

  • Both 555 ICS are connected to the breadboard.
  • 1st 555 ic connection:-
  • Pin 1st is connected to the GND.
  • Diode negative leg is connected to the pin 2 and pin 2 connected to the pin 6.
  • Diode positive leg is connected to the LDR and LDR 2nd led is GND.
  • Diode positive leg is connected to 10k ohm resistor and resistor 2nd leg is connected to the positive supply.
  • Pin 3 is connected to the 150k ohm resistor and 150k ohm resistor second leg is connected to the 470k ohm resistor and 470 k ohm resistor the second leg is connected to the pin 2.
  • Pin 4 is connected to the positive supply.
  • Pin 6 to connected electrolytic capacitor positive leg and negative leg is GND
  • Pin 8 connected to the positive supply.
  • Pin 3 is connected to the 2nd 555 ic pin 4.
  • 2nd 555 ic connection:-
  • Pin 1st is connected to the GND.
  • Pin 2nd is connected to the pin 6 and pin 2nd is connected 470k ohm resistor and resistor 2nd leg is connected to the pin 3.
  • Pin 2nd to connected ceramic capacitor and capacitor 2nd leg is GND.
  • Pin 3 to connected 100-ohm resistor and resistor 2nd leg is connected to the buzzer positive leg and buzzer 2nd leg is GND.
  • Pin 8 is connected to the positive supply.
  • Breadboard positive to positive and negative to negative connected.

WORKING

When the fridge door is open for a long time then we using fridge door alarm circuit. we open the Door of refrigerator, LDR senses it and start the countdown using 555 Timer ic for 30 seconds, and after a preset time, the buzzers starts beeping as an alarm signal.