DIY Temperature Controlled Auto Fan V1.0

Sunday, August 16, 2009

This is the first DIY project undertake to control my saltwater aquarium’s temperature, maintaining it at around 27 degree C.

Since the room temperature is about 30 degree C, by using two DC fans, blowing on the surface of the water, is able to bring down the temperature of about 2-3 degree. Therefore there’s no need to use the much more expensive approach such as using an aquarium chiller.

However to avoid the water temperature from getting too cold during the night, a simple temperature controller is used so that the fans can be turn off when the tank temperature fall less then 27 degree C

The control circuit works on a simple 741 Opamp and a 50K Ohm thermistor and a temperature sensor. The fans are controlled by a relay that will latch on from the opamp output via a transistor,

Here’s how the project looks like,




Here are the components used










The temperature probe, made of a 50K thermistor










The DC fans, two 3 inches 12VDC fans. Commonly used in PC casing








The PCB. Stripboard type









The enclosure






The final Assembly

The PCB

The Fans with holder

The complete set, inclusive of 12VDC adapter

The Calibration.

The calibration is fairly simple, I placed the probe into a warm water together with a calibrated digital thermometer. When the warm water temperature drop to 27 degree C, I turn the trimmer pot until the circuit turns on the fans. Repeat this process until and find tune the trimmer pot if the fans does not run when temperature drops below 27 degree C.