Imagine yourself putting your favorite food, beverages or something you want to eat in the refrigerator. Then you go to your bed and try to have some sleep, but somebody in your house go into the refrigerator and saw it then took it and eat it all. Sounds bad right. But, if you 'wish' you have an alarm which will tell you somebody has opened the refrigerator then this post is the right thing for you.

How does the Refrigerator Door Alarm works? The circuit, enclosed in a small box, should be placed in the fridge near the lamp (if any) or close to the opening. With the door closed, the interior of the fridge is in dark, the photo resistor R2 presents a high resistance (>200K) thus clamping IC1 by holding C1 fully charged across R1 and D1. When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance (<2K) stopping C1 charging current. Therefore IC1, wired as an a stable multivibrator, starts oscillating at a very low frequency and after a period of about 24 sec. its output pin (#3) goes high, enabling IC2. This chip is also wired as a stable multivibrator, driving the Piezo sounder intermittently at about 5 times per second. The alarm is activated for about 17 sec. then stopped for the same time period and the cycle repeats until the fridge door closes.

Problem encountered:

The piezo sounder did not work. The layout was short circuited.

Solution

The layout must be designed properly to avoid problems in the attachments of the components.

SCHEMATIC /LAYOUT /ACTUAL CIRCUIT