We suggest you make a small utility that will prevent installation, perhaps, to throw the contents of your refrigerator or your freezer in the trash. Indeed, at this time of great heat, leave the door open for such a device generally ends in disaster. Our implementation easily be housed in a small plastic box (the size of a matchbox) and battery-emit a beep when the door is opened. This is to avoid any oversight or poor closure.
This little montage made by any beginner, save perhaps the contents of your freezer
The operating principle of our design is very simple: open the door of a refrigerator causing the illumination of a systematic bulb, a photocell detects the light, and will order the start of an oscillator responsible for generating a voltage alternative. A speaker of small size will issue the alarm.
Note that all freezers are not equipped with a lighting device. However, ambient light will provide sufficient lighting for the cell to activate the device - the only case where it would be totally ineffective or that you would come to loot the contents of the freezer at night without turning on the light ... If that does not really correspond to a normal use of the camera!
Turning to the study of our assembly. His heart, the oscillator will be conducted using an integrated circuit of the type NE 555 (which we now familiar). We find him at the resistors and capacitor responsible for setting the frequency of oscillation. To control its startup, we will use the pin number 4. A transistor will amplify the voltage fluctuations resulting from changes in light intensity received by the photodetector sensitive to give them sufficient amplitude. The latter is directly connected to the tab number 4 of the integrated circuit, to ensure its startup or shutdown. The connection between the integrated circuit and the speaker shall be effected by means of a chemical capacitor. The latter's role is to remove the DC component of signal issued by the oscillator and, consequently, greatly reduce the power consumption of the assembly; important point when using batteries as a power source.
The wiring of this circuit, given the low number of components it requires for its realization is extremely simple. This will involve a realization that beginners can safely tackle. However, care should be taken to cut all conductive strips of the plate wiring in the integrated circuit, and the locations mentioned on the diagram.
Similarly, we seek to achieve a pinout of the transistor and integrated circuit, and polarity of chemical capacitors. Once wiring is complete, the stack will be implemented. In ambient light the issue of the beep will be immediate. By hiding the cell, or running into a dark room, it will stop. After doing a little test, you can install it, and this, in any place in the refrigerator or freezer. All
housing may be used for its skin. If it is opaque it will then make a hole in front of the cell. Similarly we puncture before the speaker. For
Finally note that most ordinary batteries do not work properly inside a temperature of -18 ° C. Alkaline batteries seem to be less affected by cold, and their duration is much greater.
electronic component
R2 = 220 Ohm (red, red, brown, gold)
R3 = 220 Ohm (red, red , brown, gold)
R4 = 220 Ohm (red, red, brown, gold)
R5 = 22 kilohms (red, red, orange, gold)
C1 = 1 microfarad microfarad
C2 = 47 = Ic
NE 555
T1 2N = 3905
LDR = LDR photoresistor
= HP speaker diameter 50 mm
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