PIC-based Central Heating Programmer

Central heating systems has been a good solution for many homes and even offices for quite some time now. If you own such a system I’m sure you would like to be able to control it remotely from your bed or even from a computer. This project presents such a controller. It has a 5/2 days programmer, that is 5 week days, 2 weekend days or for entire week.

The control panel allows you to turn on and off heat and hot water independently. It has 10 program entries that you can save and you have the possibility to manually override the program. Basically it is composed of two modules: the relay module that is placed at the boiler, which also has the 9 pin D connector for serial connection and the programmer panel which is connected to the relay module by a UTP cable.

The programmer panel has a 216 LCD display and five switches to select the desired program or manually control the central heating. PIC16F628A microcontroller was used in this project as the system’s brain. Dallas DS1307 was used for time management and for saving time settings in its memory. It is powered by a backup battery so it will not lose the memory data when mains power is taken. Max202 IC takes care of the serial communication.

Because of the UTP wire lenght the rellay output of the PIC can not drive the rellays directly, so a driver is used from Quasar Electronics. It is also a good idea to use protection diodes on those outputs to take care of spikes.

LCD will show the current operation mode for central heating and hot water, the on/ off state and the time. Switch 1 and 2 turns the system on/off , switches 3 and 4 are used for manual control and switch 5 is used for programmer setup. A detailed explanation of the programmer’s operation is presented in the link with all schematics and construction procedures as well as the software for the microcontroller.

PIC-based Central Heating Controller: [Link]