A digital desk clock with temperature display feature by Electro-Labs:
The brain of the circuit is a Microchip PIC18F252 microcontroller. It acquires precise time information from DS1307 real time clock via I2C interface and displays it on four digit 38 mm seven-segment display with the help of MAX7219CNG display driver. The temperature data is read by the on-chip ADC module of the microcontroller from LM335 temperature sensor which outputs 10mV per kelvin degree linearly. The temperature data is also displayed periodically.
The PIC microcontroller and the peripheral ICs mentioned above needs 5V regulated supply to operate. The step-down converter in the power section of the circuit, LM2574N-5.0, converts 12VDC input voltage to 5VDC and lets to draw 500mA without any significant heating problem.
There are two LEDs on the board indicates power and functional status and the buttons let the user adjust the time and display the temperature manually.