I have recently made a temperature controlled DC fan whose speed increases with the rise in temperature and decrease as the temperature falls ! It has got a lot of practical usage as it does not require to manually operated and it turns off as the temperature falls below a certain threshold ! and the temperatures on which you want to change the speed or turn off the fan are completely user defined !!
The components required are:
1.AT89S51/AT89S52
2.ADC0804
3.LM35
4.L293D
The components required are:
1.AT89S51/AT89S52
2.ADC0804
3.LM35
4.L293D
LM 35:
Temperature sensor whose output voltage varies with the change in the temperature. The output voltage increases by 10mV for 1 degree rise in temperature.
ADC 0804:
It is an analogue to digital converter who converts the provided analogue signal into corresponding digital signal. It uses the provided reference voltage to provide digital output from analogue input.