This project made by Ahmad Al-Shalabi and Bassma Karbouj .

The purpose of this project is creating a cooling system by controlling in a DC fan in a simple way without using Microcontrollers or Arduino but by using electronic components that it's very simple and available.

This fan works when temperature reach into pre-specified threshold.

The DC fan controlling achieved by a Thermistor and which is a type of resistor whose resistance is dependent on temperature. there is two type of thermistor that is NTC " Negative Temperature Coefficient" , PTC " Positive Temperature Coefficient " :

With NTC, resistance Decreases with temperature increase .

With PTC, resistance Increases with temperature increase .

Step 1: What's You Need ?

Dc Fan (5V).
Thermistor NTC 5K ohm (1).
LM358 Operational Amplifier (1).
LM555 Timer (1).
BC337 NPN Transistor (2).
1N4007 Diode (1).
Resistors { 10k (2) , 4.7k (2) , 470 (3) , 5k } ohm.
Variable Resistors { 100k , 500k } ohm.
Capacitors { 0.1 , 200 } MicroFarad.
LEDs.
Wires.
Battery (5V).
Test Board.

Step 2: The Circuit:

LM358 contains two operators amplifiers which we use it as a comparative.

We use the Transistors as switch.

Description :

When the Temperature increase ,the voltage drop at both ends of the thermistor will decrease , which leads to light the first led “The green Led” pointing to increasing temperature.

When the temperature continues increasing to the second threshold , the second led will light and the fan works as long as the temperature is higher than the second threshold .

When the temperature return to the allowable level " the first threshold" the fan will still work for a specific period time by the 555 IC.

The temperature thresholds and the period of fan working after return temperature to the allowable level can be modification by using two variable resistance.