Refrigerator alarm. Scheme, description

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Refrigerator alarm. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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The proposed light and sound signaling device is designed to control the position of the door of the refrigerating chamber and the temperature in it. About the left open door of the refrigerator and about too high a temperature in it, he gives light and sound signals. The operation of the signaling device is based on the fact that the light of the incandescent lamp in the refrigerating chamber, which turns on when the door is open, falls on the photocell, the voltage on which in this situation increases. To control the temperature inside the refrigerating chamber, a sensor is installed, its readings are periodically compared with a threshold equal to +15 °С.

Refrigerator alarm
Fig. 1

The diagram of the signaling device is shown in fig. 1. The MK PIC12F675 (DD1) used in it has a built-in ten-bit ADC module. Working according to the program presented in the table, the MK monitors the voltage on the BL1 photocell, the readings of the temperature sensor VK1 and outputs control signals to the microcontroller port to control the two-color LED HL1 and the sound emitter HA1. The microcontroller is configured to work with an internal clock generator with a frequency of 4 MHz, the program uses the TMR1 timer. The line of the third bit of the MK port serves as an analog input of the ADC. As a photocell BL1, a conventional red LED AL307BM is used. Chip DA1 - supply voltage stabilizer.

In standby mode, the green crystal of the HL1 LED is constantly on. When the refrigerator door is open, the green crystal goes out, but red flashes at a frequency of 1 Hz. If after 45 seconds the door is not closed, then the sound signal will turn on for 15 seconds. If the door remains open, after 45 seconds the signal will be repeated, and so on three times, after which the LED will continue to flash red, but the sound signal will no longer sound.

Refrigerator alarm

If the temperature in the refrigerator compartment exceeds 15 °C with the door closed, the red crystal of the LED will glow continuously. Three times with a period of one minute, a series of three short (1 s each) sound pulses will be repeated. After that, the LED will remain on, but there will be no more beeps.

In the event that both the door is open and the temperature has exceeded 15°C, a three-minute sequence of alarms about the open door of the refrigerator compartment will be given first, and only after that the alarms about the increased temperature will sound.

Refrigerator alarm
Fig. 2

The signaling device is made on a board made of one-sided foil-coated getinaks (Fig. 2), placed in a plastic case. Both resistors are size 0805 surface mount. They are soldered on the side of the printed conductors. The L-59EGC LED can be replaced with another two-color LED with common crystal cathodes, for example, the domestic ALS331A.

It is recommended to make the temperature sensor and the photocell remote, as they must be placed inside the refrigerating chamber. The length of the wires between them and the signaling device board can reach several meters. Since the refrigerator compartment light is a heat source, the temperature sensor should be installed away from it. The photocell, on the other hand, is placed closer to the lamp and directed with a sensitive surface directly at it.

Given the wide variety of types of household refrigerators, each with its own design features, the place for the signaling device should be chosen based on specific conditions. The HL1 LED and the HA1 sound emitter can also be removed from the board to a place convenient for observation and providing good audibility of signals. The signaling device is powered from a 9 ... 12 V DC source. This may be a suitable power adapter connected directly to the 220 V circuits inside the refrigerator.

The microcontroller program of the signaling device can be downloaded hence.

Author: V. Surov, Gorno-Altaisk; Publication: radioradar.net

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