The use of mechanical thermostat in refrigerators presents more and more disadvantages, such as temperature drift, large error, no shutdown, no starting up, and so on, resulting in a large number of customer complaints and after-sales maintenance. From a low cost point of view, a computer controller based on single chip microcomputer is introduced to replace the mechanical temperature controller.
The main hardware components and various functions of the controller are mainly introduced. Finally, the comparison between mechanical refrigerator and computer refrigerator is made in the control part. Traditional mechanical refrigerators need to manually adjust the gear of the mechanical controller to adjust the temperature of the refrigerator according to the temperature condition, so the temperature can not be accurately perceived; mechanical refrigerators need the temperature to rise to a certain difference before the controller can start again, the temperature fluctuation is relatively large, which has adverse effects on food storage and energy consumption.
In recent years, with the continuous improvement of people’s material life level, the demand for refrigerators is getting higher and higher. The disadvantages of mechanical refrigerator, such as large temperature error, no shutdown, hard to start up, little function and low grade, are becoming more and more difficult to accept. Based on this, every big refrigerator factory develops computer temperature control refrigerator, uses the electronic temperature sensing head to perceive the internal temperature of the refrigerator, and can accurately measure the temperature. By controlling the opening and stopping of the compressor by computer, the temperature is kept at an accurate value, so that the temperature control is accurate and the function is more and more. It meets the needs of some high-end users, but the high cost hinders people’s desire to purchase, and the mechanical fridge still occupies most of the market. The following is a low cost computer controller, which is applied in a direct cold single cycle refrigerator with ingenious electrical design and beautiful appearance design.
The effect is very good. * Switching power supply part: adopt strong and weak electric safety isolation design, output 12V/0.15A.
Because the output power is small, thermostatic element the original excitation mode is adopted, and the OB2226CP switch chip is used to drive the device. The device has fewer components, less standby power consumption, and the output 12V is stable and reliable.
At the entrance of the power supply, it is necessary to add a fuse to carry out overcurrent protection, to carry out surge protection for varistors, and to exchange filters with X2 safety capacitors.
These three components are directly related to the safety and electromagnetic compatibility of the controller, so it is essential and necessary to obtain the safety certification of the sales country. * MCU and peripheral circuit: MCU uses ST STM8S003F, 16 I/O ports, 8K flash ROM, 1K RAM. Using the internal oscillation of the chip, the external crystal oscillation is omitted. RC reset circuit and single-line interface module (SWIM) are used to debug and write programs. The peripheral circuit is very simple. * Input and output circuit: Input signal has three temperature sensors (refrigerated air sensor, evaporation sensor and environment sensor), two key signals and a door switch signal; Output control signals include: AC load compressor and incandescent lighting, seven LED indicator lights, and one buzzer.
Compressors are controlled directly by relays; incandescent lamps are controlled by thyristors because they require adjustable power for lighting and low temperature compensation. * Key and indicator circuit: 7 LEDs adopt 2X4 matrix circuit, two keys are hung on two COM lines of matrix circuit at one end, multiplexed with matrix circuit in time sharing, and one I/O port is used to receive key signal at the other end. In this way, 7 I/O ports are used to solve 9 signals that need to be processed.
Temperature gear is indicated by five LED lights, and intelligent mode and quick-freezing mode are indicated by two LED lights respectively. Refrigeration room temperature can be set to 2, 4, 5, 6, 8 C. Press the refrigeration key, you can adjust the temperature of the refrigeration room.
Every time you press it, the setting temperature will be switched to the next temperature, which can be set circularly. Refrigeration in refrigeration room is controlled by air temperature sensor and defrosting temperature sensor in refrigeration room. When the temperature of air temperature sensor (Tr) is higher than the start-up temperature (Trk) and the temperature of defrosting temperature sensor (Trd) is higher than 5 C, the refrigeration stops when Tr is lower than the stop temperature (Trt). The temperature of the refrigeration chamber is automatically matched by the refrigeration system to maintain the low temperature state specified in the national standard. Press the “mode” button, select the intelligent mode, the intelligent indicator lights up; enter the intelligent mode. Press the “mode” button, select the quick-freezing mode, the quick-freezing indicator lights up; enter the quick-freezing mode. In this mode, the starting and stopping points of the press are set according to the lowest refrigeration temperature. Lamp compensation, asynchronous with press. After 54 hours of operation, the system automatically exits and returns to the mode before the quick-freezing mode is set. Buzzer control: open door music prompt sound. Keyboard prompt sound: The buzzer whistles when the key is pressed. Door open alarm: When the refrigerated door opens, if the user forgets to close the door, the alarm will start 90 seconds later. The alarm will ring five times every 30 seconds (0.5 seconds a cycle), and then repeat the cycle until the door is closed. At the same time meet: Tr 5 minutes), the press power off. * In the case of non-first power-on, the following conditions can be met simultaneously: Tr (> Trk and Trd (> 5 C); the compressor stops working for more than 5 minutes; in the case of first power-on, the compressor will be energized after 3 seconds of power-on. Lighting control: Refrigerator door lights on, the door lights off. Exit condition: If the temperature of the environmental sensor is higher than 17 C, or the temperature of the sensor of the refrigerated evaporator is higher than 17 C, the lamp compensation will stop working. The refrigeratory automatically operates in the set mode before power failure when it is powered on again after power failure. The data to be memorized include the setting temperature and operation mode of the refrigeratory. When the temperature inductor is open or short circuit, it is called fault state. In the fault state, quit intelligent and quick-freezing, and its corresponding LED flash alarm.
When the environmental temperature sensor fails, it should be treated according to Th=25 C, and the quick-freezing and intelligent indicator flash alarm. When the temperature sensor in the refrigeration space is out of order, the flash alarm of the indicator lamp at 2 and 4. Compressor is operated for 20 minutes and closed for 20 minutes. When the refrigeration defrosting temperature sensor fails, the flash alarm of the indicator lamp at 5 and 6.
Compressor is controlled by refrigeration temperature sensor, defrosting temperature sensor does not participate in the control. The compressor is allowed to start after 3 seconds of power-on; the normal shutdown time of the compressor should be more than 5 Min each time. From the above cost comparison, the cost of a computer refrigerator is only 8.64 yuan higher than that of a mechanical refrigerator. Conclusion: the function and cost comparison of the computer thermostat introduced above can only increase the amount of less than 10 yuan, and realize the above functions of the mechanical refrigerator which can not be realized at all. This makes the grade of the refrigerator a great step, which greatly improves the price performance ratio of the refrigerator, and achieves considerable economic and social benefits.