- INTRODUCTION:
- Celsius scale thermometer displays the ambient temperature through a LCD display. It consists of two sections. One is that which senses the temperature. This is a temperature sensor LM 35. The other section converts the temperature value into a suitable number in Celsius scale which is done by the ADC0804.
- A digital thermometer can be
easily made by interfacing a temperature sensor to the micro controller
AT89C51. The temperature sensor used in the project is LM35. 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 8051 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.
- The step size is defined by the
voltage applied at the Vref/2 pin of the ADC I. For example, if
the voltage at VRef/2 pin is set to 1.28V then ADC has a step size of 10 mv.
So if the input voltage is 1V the equivalent binary output of ADC will be
100 or 0110 0100 in binary.
- The 8 bit binary output of the
ADC is incremented by one for every 10 mv rise of input
voltage. Different step size can be selected by changing the voltage
input to the Vref/2 pin.
- The step size of the ADC
is calibrated using a preset to match the actual temperature. Once the ADC
is calibrated it will give the correct output further. The binary
output of ADC is fed parallel to a port of the micro controller .The micro
controller reads the input through ADC and displays the corresponding
decimal value on LCD indicating the temperature.
BLOCK DIAGRAM:
DOWNLOAD: SOURCE CODE
1 comments:
nice.
uplode now projects.
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