Design of fan temperature control system based on single chip microcomputer

0. Introduction
Fans are general-purpose machines, which are widely used in various sectors of the national economy. Fans are widely used in ventilation, dust removal and cooling of factories, mines, vehicles, buildings, household appliances, etc.; drying and selection of grains; wind tunnel wind source and inflation and propulsion of hovercraft, etc. In addition, in some places with special requirements for ambient temperature, the temperature change is required to be below 1°C, which requires a fan temperature control system that can determine the rotation and stop of the fan according to the external ambient temperature.
The fan micro-temperature control system designed in this paper can achieve a temperature detection accuracy of 0.01°C, and the upper and lower temperature limits can be manually set, and it has an automatic sound and light alarm function.

1. Design requirements
This system uses a PT1000 temperature sensor to detect ambient temperature (temperature detection accuracy 0.01°C), controls the fan cooling according to ambient temperature changes, and has functions such as manual setting of temperature upper and lower limits, sound and light alarms, etc. The schematic diagram of its control panel is shown in Figure 1.

The specific technical requirements and functional descriptions are as follows:
(1) When the ambient temperature is within the set temperature range, the green LED is on and the fan does not work;
(2) When the ambient temperature is close to the set temperature upper limit (within 5°C), the yellow LED is on, the fan works at low speed, and the buzzer emits three 500Hz alarm sounds;
(3) When the ambient temperature is higher than the set temperature upper limit, the red LED is on, the fan works at full speed, and the buzzer sounds for a long time.
(4) The dual fans are used to work in time-sharing mode for easy maintenance.

2. Design of fan temperature control system based on single chip
microcomputer 2.1 System hardware design
2.1.1 System hardware composition
According to the design requirements, we adopt a modular design scheme for the fan control system, and divide the entire fan temperature control system into nine functional modules, namely: power module, fan control module, main control circuit module, display circuit module, key module, alarm module, temperature detection module, EEPROM module, serial communication module, etc. The relationship between each functional module is shown in Figure 2.

2.1.2 Introduction to each functional module of the system
(1) Power supply module
System power supply: external 12V/2A DC power supplyDigital power supply: 51 single-chip microcomputer, AD conversion chip, optocoupler. Use 1 7805 three-terminal voltage regulator. Analog power supply: The fan is directly connected to the 12V power supply, and the PT1000 sensor is powered by 1 7805 three-terminal voltage regulator. Device requirements: 1 12V/2A DC power supply, 2 7805 three-terminal voltage regulators, 1 power indicator light, and 1 power switch.
(2) Fan control module (fan control adopts master-slave mode) This module uses 1 single-chip microcomputer IO port to output PWM signals, and controls the fan's stop and speed through optocouplers and MC1413 drive circuits. The fan is powered directly by 12V power supply. The circuit diagram is shown in Figure 3.

Device requirements: 2 0.8A fans, 1 MC1413 driver control chip, 2 6N137 optocouplers. [page]

0. Introduction
Fans are general-purpose machines, which are widely used in various sectors of the national economy. Fans are widely used in ventilation, dust removal and cooling of factories, mines, vehicles, buildings, household appliances, etc.; drying and selection of grains; wind tunnel wind source and inflation and propulsion of hovercraft, etc. In addition, in some places with special requirements for ambient temperature, the temperature change is required to be below 1°C, which requires a fan temperature control system that can determine the rotation and stop of the fan according to the external ambient temperature.
The fan micro-temperature control system designed in this paper can achieve a temperature detection accuracy of 0.01°C, and the upper and lower temperature limits can be manually set, and it has an automatic sound and light alarm function.

1. Design requirements
This system uses a PT1000 temperature sensor to detect ambient temperature (temperature detection accuracy 0.01°C), controls the fan cooling according to ambient temperature changes, and has functions such as manual setting of temperature upper and lower limits, sound and light alarms, etc. The schematic diagram of its control panel is shown in Figure 1.

The specific technical requirements and functional descriptions are as follows:
(1) When the ambient temperature is within the set temperature range, the green LED is on and the fan does not work;
(2) When the ambient temperature is close to the set temperature upper limit (within 5°C), the yellow LED is on, the fan works at low speed, and the buzzer emits three 500Hz alarm sounds;
(3) When the ambient temperature is higher than the set temperature upper limit, the red LED is on, the fan works at full speed, and the buzzer sounds for a long time.
(4) The dual fans are used to work in time-sharing mode for easy maintenance.

2. Design of fan temperature control system based on single chip
microcomputer 2.1 System hardware design
2.1.1 System hardware composition
According to the design requirements, we adopt a modular design scheme for the fan control system, and divide the entire fan temperature control system into nine functional modules, namely: power module, fan control module, main control circuit module, display circuit module, key module, alarm module, temperature detection module, EEPROM module, serial communication module, etc. The relationship between each functional module is shown in Figure 2.

2.1.2 Introduction to each functional module of the system
(1) Power supply module
System power supply: external 12V/2A DC power supplyDigital power supply: 51 single-chip microcomputer, AD conversion chip, optocoupler. Use 1 7805 three-terminal voltage regulator. Analog power supply: The fan is directly connected to the 12V power supply, and the PT1000 sensor is powered by 1 7805 three-terminal voltage regulator. Device requirements: 1 12V/2A DC power supply, 2 7805 three-terminal voltage regulators, 1 power indicator light, and 1 power switch.
(2) Fan control module (fan control adopts master-slave mode) This module uses 1 single-chip microcomputer IO port to output PWM signals, and controls the fan's stop and speed through optocouplers and MC1413 drive circuits. The fan is powered directly by 12V power supply. The circuit diagram is shown in Figure 3.

Device requirements: 2 0.8A fans, 1 MC1413 driver control chip, 2 6N137 optocouplers.

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Taking the fan control module as an example, the system software design source program is given:

3. Conclusion
This paper designs a fan temperature control system based on a single-chip microcomputer. It can collect data through a temperature sensor according to slight changes in ambient temperature and control the fan's action after signal processing. The control system adopts a modular design, has high reliability and is easy to maintain. It has been verified by experiments that it can achieve the intended function.