Thermostat itself isn’t very complex device. All it has to do is to take temperature readings using some sort of sensor and depending on threshold value switch on or off power switch. Basically you don’t need any indicators to work it properly. Ktulu wanted a bit more than simple thermostat. As a basic set up he has chosen a PIC16F74 microcontroller which takes temperature readings using DS1820 1-wire temperature sensor.
He had Siemens M55 color LCD around and decided to use it as indicator. Using graphical LCD he added selectable 1 hour or 10 hour graph. It is convenient to see how temperature were changing during time. Small menu system with couple push-buttons enables to change some parameters like threshold temperature values. Also thermostat is equipped with LDR resistor which senses night time and adjusts preset temperature to other preset value. The thermostat were originally used to regulate boiler according to room temperature. Together with inner boiler regulator it helps saving energy.