PIC-based Thermostat

Summer is here for those of us in the northern hemisphere and heat becomes a problem again. Fear not for here is a project for you to build your own room temperature controller.

This device uses two sensors to monitor temperature at two locations, inside and outside for example and depending on the measurements, it controls two external devices like cooling fans for example. Relays are used to turn on or off these external devices. You can chose to trigger the relays when the outside temperature becomes too high or when inside temperature becomes too low.

The microcontroller used is a PIC16F873 and controls all functions of the device. Port B drives the 7 segment LEDs, Port C is used for device designation, Port A controls the Relays.

The temperature sensors are LM35DZ. These sensors can measure from 0 degrees to 100 degrees Celsius and outputs 10mV per Celsius degree. However the 0V level is given at 2 degrees Celsius and since the project doesn’t use a symmetric (+/-)  power supply it’s lowest temperature that can be measured will be the 2 degrees Celsius. The sensor’s output after being amplified by LM358 Opamp is sent to PIC’s analog input.

The 7 segment LED display will show the inside temperature, the outside temperature and the preset temperature. The preset value is the threshold that will trigger the external devices. While this project is designed to maintain the room temperature around a certain value, the principle can be used in many projects like in one of those incubators where u can control a fan and a resistive heating element.

In the end i must say this is a very well documented project and everything is explained in great detail. The information is very well structured and besides complete schematic and code everything is very well explained step by step, including the actual building process. Happy soldering.

PIC-based Thermostat: [Link]