LED Temperature Display Integrated with Digital Thermostat

The project illustrates an advanced digital thermostat that employs the PIC18F1320 microcontroller wherein three multiplexed LED displays were allowed to be driven while easily reading the temperature from a digital sensor.

In fully powered mode, the microcontroller mode communicates with a 1-wire digital temperature sensor. The temperature display resolution is not affected by the choice of sensor. The three high efficiency LED single digit common cathode type display segments are driven by the controller. The current is limited within the 25mA per pin drive through series 510Ohm resistors. The average current is effectively reduced with the multiplexing action. The two pins normally used for connecting a crystal are freed up using the on-chip oscillator making the pins used as ports.

For configuration, two tactile pushbuttons are used. The config mode can be entered using the SET/DOWN button while reducing thermostat temperature. The config values or temperature is increased with UP button. A short press of the UP button displays the minimum and maximum temperatures logged since power-on. A 12V DC supply is used to power the circuit while the microcontroller and display is supplied by the low power 78L05 5V regulator.

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