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Sneaking in the Fridge?



Sounds are coming from the kitchen late at night. One morning a slice of pie is mysteriously missing. What's going on? Who's sneaking into the fridge? Build this simple alarm circuit to catch the midnight snacker in the act! When the refrigerator door is closed, the alarm is quiet. When the refrigerator door is open, the inside light switches on and activates the alarm, which emits a shrill tone. Even if the tone fails to wake you, it just might cause the fridge invader to quickly close the door and return to bed.

Sneaking in the Fridge?

step 1How it works...

The circuit for the fridge alarm is shown in Fig. 1. It's a basic light-activated switch that activates a piezo tone generator. When cadmium sulfide photoresistor R1 is dar…

step 2Parts You Will Need...

The following parts were used to make a prototype circuit on a solderless breadboard. Jameco part numbers are shown in parentheses. Q1-- 2N2222A NPN transistor ([http:ww…

step 3Prepare the Board and Install the Components...

The circuit was assembled on a solderless breadboard and tested. When the circuit was operating properly, the components were transferred to a perforated prototype board (J…

step 4Solder the Connections...

After the components are installed, turn the board over and solder the component leads together according to the circuit diagram in Fig 1. Or refer to Fig. 4 and follow th…

step 5Test the Circuit...

Connect a fresh 9-volt battery to the connector clip. The PZ may or may not emit a tone. Use a small screwdriver to adjust R2 until PZ emits a tone. Place a finger over th…

step 6Going Further...

This circuit has other applications. For example, it's a great daylight alarm clock. Add a pushbutton switch between the positive battery connection and the circuit, and i…

Via Instructables, Published: 2009.05.30


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http://www.instructables.com/id/Sneaking-in-the-Fridge/