Description |
This project it´s based on a PIC18F25K20, with the purpose of control
a FAN with PWM (Pulse with Modulation). It offers a variable speed
control, low acoustic noise, reliability, long lifetime, low power
consumption, protection features. The MCU get the temperature from
the sensor (D18B20), and after will do a conversion Celsius degrees
and then it´s generated a PWM on PORTC.2 with 6 different levels.
PWM | TEMPERATURE |
15% | <= 49° |
30% | 50° |
40% | 51° |
50% | 52° |
75% | 53° |
100% | >54° |
After the signal goes to Q1 (BC338) in order to control the duty cycle
in the fan. I had to use two transistors to have an Ic on Q2 to be
enough to activate the fan. Because the MCU only generate a maxim
of 3.6V on which output, and 15% of 3.6V is 0.5V to polarize Q1 we
need 0.7V.
How to calculate the Q1 and Q2:
You will be able to control the FAN between 5V and +/-12V.The BC338
have a current load of 800mA that is value of a fan can have, you can
use two or more fans as long the current load isn´t more than 800mA.
The output of MCU connect to the Q1 and Q2 it works like a switch,
the D3 it´s for protection from the magnetic field in the inductors
from the FAN, without the D3 when you turn off the system the
current will be discharge to the Q2 and could damage it.
Connectors | |
| J1 | Expansions PORTS |
| Source | 12V |
| Sensor | D18B20 |
| FAN | Connect the FAN |
| ICSP | To program with PICKIT2 |
Photo of the prototype on perfboard
Schematic |
PCB |
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