Convenient and practical computer automatic temperature controller

This computer temperature automatic controller can automatically adjust the speed and start and stop of related fans according to the temperature, and display the temperature of each place in turn, saving energy and reducing noise, easy to use, and does not occupy system resources.

1. Working Principle

The working principle of this device is shown in the figure below. IC2 is the main control chip AT89S51, IC4 is the 8-bit successive approximation A/D conversion chip ADC0809, RT1~RT4 are thermistors for measuring the temperature of CPU, power supply, chassis, and graphics card, respectively, and FAN1~FAN4 are fans for controlling the temperature of CPU, power supply, chassis, and graphics card, respectively. Taking CPu temperature control as an example, when the temperature rises, the resistance of RT1 decreases, and the voltage at point A increases. The changed voltage enters the input channel IN0 of ADC0809 as the analog quantity to be converted, and is converted into a temperature value after AD conversion and table lookup and displayed on the digital tube. The leftmost digit displays "1" (1 represents CPU, 2 represents power supply, 3 represents chassis, and 4 represents graphics card), the second digit on the left is not displayed, and the last two digits display the actual temperature value of the CPU. The display range is 0~70℃. When the temperature is lower than the set lower limit of temperature, the microcontroller sends a control instruction through the serial port and is shifted and output through 74LS164. V5 and V9 are cut off, and the fan FAN1 stops rotating.

When the temperature is higher than the lower limit but lower than the upper limit, V5 is saturated, V9 is cut off, and the 12V power supply is reduced by VD1 to 9V and added to both ends of FAN1, so that FAN1 runs at a low speed. When the temperature is higher than the set upper limit, V5 and V9 are saturated, and the 12V voltage is all added to FAN1, and FAN1 runs at full speed to cool the CPU. The temperature control of other places is the same. When working normally, the digital tube displays the current temperature value of 4 channels in turn, and the display time of each channel is 8 seconds. In the figure, AN1~AN3 are buttons for temperature setting. When setting, press AN1. The first digit on the left of the digital tube displays "1", the second digit displays "H", and the last two digits display the current upper limit temperature setting value of the CPU. Press AN2 to set the tens digit of the upper limit value, and press AN3 to set the ones digit of the upper limit value. After setting, press AN1 again, the CPU upper limit temperature setting value is written into 24C02 for permanent storage. At the same time, the digital tube displays "1L" and the current lower limit temperature setting value of the CPU. After setting the lower limit value in the same way, press AN1 for the third time, the CPU lower limit temperature setting value is written into 24C02, and the digital tube displays "2H" and the current upper limit temperature setting value of the power supply. In the same way, set the upper and lower limits of the power supply, chassis, and graphics card temperatures in turn, and then press AN1. The digital tube will display the current temperature values ​​of each location again.

2. Software Design

The program in this paper adopts modular programming. Considering the nonlinear change of thermistor resistance with temperature, the temperature value calculation is realized by table lookup, and A/D conversion is programmed by waiting. The addresses of the four channel registers are 7FFOH~7FF3H. The whole program consists of the main program, temperature judgment program, upper and lower limit setting program, A/D conversion program, table lookup program, binary-to-decimal conversion program, display program, key scanning program, key waiting release program, serial port sending program, 24C02 reading and writing program, etc. The main RAM allocation in the chip is as follows: 28H stores the key code, 29H stores the ANl key sequence, 34H and 35H are decimal conversion temporary storage units, 40H~43H are display buffers, 49H is the 12C addressing byte write storage unit, 4BH is the addressing byte read storage unit, 4DH stores the number of transmitted bytes, 4EH is the data sub-address storage unit, 50H~57H respectively store the upper and lower limit setting values ​​of the temperature of the CPU, power supply, chassis, and graphics card. 5AH is the fan operation status temporary storage unit.

3. Installation and debugging

Since the device uses a serial EEPROM memory 24C02 to save data, the set value can be saved for a long time. It can run without re-entering data each time it is turned on, which greatly enhances the practicality of the device. When it is run for the first time after being made, the fan may not rotate at all. This is because the 24C02 used is a blank chip. You only need to set the upper and lower limits of the temperature of each channel according to the above method. The power supply of this device is 12V and 5V, which can be directly taken from the redundant plug of the host power supply. RT1, RT2, and RT4 can be fixed to the bottom of the groove of each heat sink with thermal conductive glue. Since the thermistor is under the fan, in order to make it truly reflect the temperature of the heat sink, it is best to apply a thicker layer of universal glue or hot melt glue on its surface after fixing it with thermal conductive glue. RT3 can be fixed in a suitable place in the upper middle part of the chassis. In actual use, it is generally more appropriate to set the lower limit value to about 25℃ and the upper limit value to about 40℃. Since the control instructions are serially output, this device has a lot of room for expansion. For example, hard disk fans and display fans can be added as needed. In this case, only a slight change in the software is needed. Of course, this device can also be used in other places where temperature control is required.