Temperature Logger hardware schematic

In this project we use a PC for GUI display and the homemade data converter board using the AVR microcontroller. The circuit is built with the ATmega8. The chip has the onchip 10-bit resolution A/D Converter. Temperature sensor are connected to the 6 channels ADC input. You can connect up to 8 sensors with the ATmega8 TQFP package. Schematic for the ADC board is shown in Figure 1. The board consists of the ATmega8, the temperature sensor (LM335), and the serial interface. The on chip firmware controls reading the ADC converter, receives commands from PC and sends the reading to PC. The microcontroller is running with 8MHz crystal oscillator, if we use the internal RC oscillator, the external crystal may be omitted. The ATmega8 DIP version has 6 channels analog input. If you need up to 8 ADC input, you can use ATmega8 in TQFP package, or you can use another AVR microcontroller with the on-chip ADC.

We use LM335 temperature sensor. It can measure the temperature using two wires remotely. The chip produces an output signal that is proportional to the Celcius temperature scale. The trimmer POT is used to calibrate the correct output voltage at known temperature, for example 2.98V @ 25° C.



source :http://www.kmitl.ac.th