Quite easy and inexpensive to equip a domestic refrigerator alarm "door open" push on loosely covered with doors. For this device, you will need only 2-3 type photodiode FD-320 or the like, connected in series:
The detector is mounted on a removable canopy interior light of the refrigerator chamber, turn on automatically when you open the door. Photodiodes are glued with glue "Moment" on the inside of the shade at the location of the light bulbs. The connection of photodiodes consistent. The power pins fluster thin mounting wire and fixed on the ceiling with glue gun. From "musical greeting card" retrieves disk (hour) battery, it is now not needed, it is the role of the photodiodes. At free contacts fluster wires from the photodiodes, respectively, plus and minus.
Musical card also is fixed with glue on the surface of the canopy. The finished ceiling (see Fig. 2) is mounted in place, now when opening the refrigerator door simultaneously with the lighting of lamp illumination will hear a pleasant melody. As the refrigerator is opened for a short time, the same sounds and the device. If the refrigerator door is covered with a loose, the sound continues.
The monotonous sound soon get bored, as the sound of the alarm clock in the morning, so as an alternative of sound you can use a digital recorder on a single chip, it is necessary only to change the schema and find the power source, but the reward will be the sound of Your favourite phrase.
Author: I. V. Ankudinov: aiv55 [dog] mail.ru; Publication: www.cxem.net