- independent control of two fans
- maintaining a constant temperature controlled device
- fan speed is dependent on temperature
- power: 12 DC
scheme (rice. 1) It consists of two identical functional blocks, the heart of which is the chip – operational amplifier IC1 - LM358N. It enhances the voltage, taken from the temperature sensor output LM35, established by a series of connected resistors R4 and PR1 (R8 and PR2). transistor BD139 (T1, T2) connected to the output of the operational amplifier, which it has the emitter voltage, equal to the voltage at the output of the operational amplifier. At power up all of the components have a temperature, equal to ambient temperature, and the output voltage of the operational amplifier IC1 will be approximately 6 AT. This value is not enough to run the fans. Therefore, immediately after turning on the power supply for a while the fan receives full voltage, allowing it to run safely.
Assembly and adjustment
Printed circuit board device shown in Figure. 2. Setting circuit is very simple and boils down to setting up the fan activation temperature by mounting potentiometers. The easiest way – heat the sensor to a predetermined temperature, and then using a potentiometer to adjust the fan switching point.