The NXP PCF8583 IC is a clock/calendar circuit based on a 2048-bit static CMOS RAM organized as 256 words by 8 bits. Addresses and data are transferred serially via the two-line bidirectional I2C-bus.

The output voltage is 10mV/ºC . The output voltage is converted by the AD convertor of the AT Mega8. The temperature is displayed on an LCD module. In this example the thermometer has a range of 0ºC to 40ºC and a resolution of 0.5ºC. If you want to have a readout in Fahrenheit you can use the LM34.

 

Circuit Schematic

In the circuit the LM35 is connected to the ADC port of the ATMega8. The ATMega8 uses a crystal as an oscillator for the clock pulses. At PORTD of the ATM8 an 20x4 LCD display is hooked to display the temparature in a discrete value and in a analog bar.

LCD Thermometer LM35_sch.jpg

Software

The software for this project is written in BASCOM AVR. The BASCOM AVR compiler has build in commands for reading out the ADC port of a AVR microcontroller. The result is displayed on a LCD module in a discrete value of the temperature and in a bar-graph. The AT Mega8 has a A/D converter which can give an output of 210 = 1024 discrete values. When a 5V supply is used you have a resolution of 5000mV/1024 = 4.8mV. Because the LM35 has a output of 10mV/C the resolution of the thermometer is 10mV/4.8mV ~ 0.5ºC . The LCD module has 20 columns. In the scale of 0ºC to 40ºC every column represents 2ºC . You can download the BASCOM progam below.