post details Interfacing-LM35-Temperature-Sensors-8051-Microcontrollers | Interface-lm-35-89S51-89S52-Microcontrollers
Interfacing LM35 Temperature Sensor 8051 Microcontrollers

Atmel, NXP, Philips, 8051, 8052, 89C51, 89C52, 89S51, 89s52, 89C1051, 89C1051, 89C2051, AT89C4051, AT89S8252,l AT89C1051, AT89C2051, AT89C4051,P89C51RB+, P89C51RC+, P89C51RD+, P89C51RB2Hxx, P89C51RC2Hxx, P89C51RD2Hxx, P89C660, P89C662, P89C664, P89C668, P89C669, P89C51RA2xx, P89C51RB2xx, P89C51RC2xx, P89C51RD2xx, P89C60X2, P89C61X2,P89LV51RB2, P89LV51RC2, P89LV51RD2, P89V51RB2, P89V51RC2, P89V51RD2, P89V660, P89V662, P89V664.
 LM35 Temperature Sensor Introduction and FundamentalsThe LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not require any external calibration or trimming to provide typical accuracies of C at room temperature and C over a full -55 to +150C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35's low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 A from its supply, it has very low self-heating, less than 0.1C in still air. The LM35 is rated to operate over a -55 to +150C temperature range. A digital thermometer can be easily created by using LM35 temperature sensor and can be interfaced any microcontrollers.
   LM35 Temperature Sensor Introduction and Fundamentals  
The LM 35 IC generates a 10mV variation to its output voltage for every degree Celsius change in temperature. The Output of the temperature sensor is analog in nature so we need an analog to digital converter for converting the analog input to its equivalent binary output. The ADC 0804 is the analog to digital converter IC used in the project. 0804 is a single channel converter which converts the analog input up to a range of 5V to an equivalent 8-bit binary output.

Calibrated directly in Celsius (Centigrade)
Features of LM35 Temperature Sensors - 8051 Microcontrollers
Linear + 10.0 mV/C scale factor
0.5C accuracy guarantee able (at +25C)
Rated for full -55 to +150C range
Suitable for remote applications
Low cost due to wafer-level trimming
Operates from 4 to 30 volts
Less than 60 A current drain
Low self-heating, 0.08C in still air
Nonlinearity only C typical
Low impedance output, 0.1 Ohm for 1 mA load

This Digital Thermometer Design can be integrated by using the 8051 microcontroller and analog to digital converter IC ADC 804 and interfaced with any microcontroller AT8051, AT8052, AT89C51, AT89C52, AT89S51, AT89s52 and the output can be displayed on any output device may be computer monitor or any LCD display. The sensor used for this design is the LM35 which output an analogue voltage per centigrade Celsius. A circuit amplification is done between the LM35 and the microcontroller.
Interfacing LM25 Temperature Sensor With 8051 Microcontroller
The ADC804 is an analog to digital converter whic is used to convert analog signals to digital so that any microcontroller can sense the signal and works accordingly. Resolution of this IC is 8 bits and works with +5V. If input voltage 5V then converted digital output is FF.
Pin description of ADC805 :
CS : Chip Select:
It is an active low input used to activate the ADC804 IC. To activate ADC804, this pin must be low.
About ADC 804 Analog To Digital Converter
RD : Read:
It is an active low input used to get the converted data out of the ADC chip. The ADC converts the analog input to its binary equivalent and holds in an internal register. When a CS = 0 and high-to-low pulse is applied to the RD pin, then 8-bit digital output is available at the D0-D7 data pins.
WR : Write:
This is an active low input used to inform the ADC to start the conversion process. ADC starts converting analog input to digital, when CS = 0 and a low-to-high pulse is applied to WR pin. The amount it takes to convert varies depending on the CLK IN and CLK R values. When the data conversion is complete, the INTR pin is forced low by the ADC804.

Here ADC 0804 is connected to port1 of 8051. WR and INTR of ADC is connected to P3.4 and P3.5 respectively. Analog input is applied to pin 6 of ADC. Here WR is the start of conversion and INTR is the end of conversion.
Interfacing Circuit ADC 804 Analog To Digital Converter with 8051 Microcontroller