Top Electrical Mini Project on Fridge Door Alarm Circuit
- Jun 16, 2015
- 2 min read
Electrical mini projects are as important as the other big projects. Both the types of the projects are intended to sharpen up methodological approaches of the electronics engineering students, no matter to which university and which country they belong. This mini project on fridge door alarm circuit is typically designed for the final year students.
Using a 3V battery supply this fridge door alarm should be made in a small box. Then it should be placed inside the fridge close to the lamp or near to the opening. The photo resistor R2 with the door closed presents the greater resistance (>200K). In consequence it clamps IC1 by holding C1 completely charged R1 and D1 transversely.
The photo resistor lessens its resistance (<2K) stopping C1 charging current as soon as a ray of light enters from the opening, or the fridge lamp illuminates. For that reason IC1, starts oscillating at a very low frequency wired as a non-stable multivibrator, and its output pin (#3) goes high after an interlude of about 24 sec, enabling IC2.
Wired as a non-stable multivibrator this chip also compels the Piezo sounder from time to time, at about 5 times per second. For about 17 sec. this alarm is activated, and then is stopped up for the similar stretch of time. This cycle go over until the fridge door is closed again.
Few annotations for the fridge door alarm:
Shifting C1 and/or R3 standards delay time can be assorted.
Shifting C2 and/or R4 standards beeper recurrence rate can be assorted.
Current drawing of Stand-by: 150µA.
At the time of defrosting put the circuit next to the lamp. To evade circuit harm as a result of extreme moisture, take it away.
Try not to put this device in the freezer.
Fridge door alarm circuit diagram:
Components Values:
R1 = 10K 1/4W Resistor R2 = Photoresistor (any type) R3 = 2M2 1/4W Resistor R4 = 1M 1/4W Resistor C1= 10µF 25V Electrolytic Capacitor C2 = 100nF 63V Polyester Capacitor D1 = 1N4148 75V 150mA Diode IC1, IC2 = 7555 or TS555CN CMos Timer ICs BZ1 = Piezo sounder (incorporating 3KHz oscillator) B1 = 3V Battery (2 x 1.5V AA, AAA or smaller type Cells in series)
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