Temperature sensors are widely used in electronic equipments to display the temperature. You can see the digital clock displaying the room temperature value. It is due to the temperature sensor embedded in it. Generally, temperature value is analog. It is converted to digital value and then it is displayed. This article describes the same converting analog value to a digital value.
Digital Temperature Sensor Circuit Principle:
The main principle of this circuit is to display the digital temperature value. Here, ATmega8 microcontroller is used. The ATmega8 has inbuilt analog to digital converter with six multiplexed channels. This reduces interfacing of external analog to digital converter IC. The analog temperature value is directly applied to input ADC channels of microcontroller. Successive approximation method is used for Analog to digital conversion internally.
Digital Temperature Sensor Circuit Design:
The digital temperature circuit consists of ATmega8 microcontroller, LM35 temperature sensor, 7 segment display. The temperature sensor Lm35 is connected to one of the ADC channels of microcontroller.
ATmega8 has six ADC channels at Port C. PC0-PC5 pins of Atmega8 act as ADC channels. This shows that one can interface six analog values. But only one conversion is done at a time depending on the priority of the input channels. The resolution of ADC is 10 bit. Remember that for conversion Vref and Avcc are externally connected as shown in circuit.
Generally, all the port pins of ATmega8 microcontroller act as normal input /output pins until their special functions are declared. ADC registers inside the controller have to be declared in order make Port C to act as ADC channel.
Lm35 temperature sensor has three terminals. Placing the flat surface towards you first pin is Vcc, Second pin is Output and the third pin is Ground. Output pin of temperature sensor is connected to the first ADC channel i.e. PC0 pin of microcontroller.
Seven segment display has eight pins and one common pin. Leaving Dp, connect all the seven pins to port B. Connect A to PB0, B to PB1,_____, G to PB6. Seven segment display used here is common cathode display. Current limiting resistors were used between controller and the display.
For more detail: Digital Temperature Sensor Circuit