30-01-2013, 09:11 AM
Temperature Mounting System by using microcontroller 89c51
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Introduction
The Aim of our project “Temperature Mounting System by using microcontroller 89c51” to measure the temperature with the help of temperature sensor and display it on the LCD. So it is a open loop system. By slightly modifying the program we can used the same project for controlling the temperature i.e. same program is used as thermostat.
Lot of embedded systems micro controllers needs to take analog input. Most of the sensors & transducers such as temperature, humidity, pressure, are analog. For interfacing these sensors to micro controllers we require to convert the analog output of these sensors to digital so that the controller can read it. Some micro controllers have built in Analog to Digital Converter (ADC) so there is no need of external ADC. But in 8051 microcontroller does not consist of on chip ADC. In our project we interface ADC 0808 to the microcontroller with the help port 1 lines of 8051 and to that ADC we connect the temp sensor LM 35 with the help signal conditioning circuit constructed by using Op-Amp 741. The measured temperature is continuously displayed on the LCD display.
Functional description:
The sensor has a sensitivity of 10mV / oC. The output of LM35 is amplified using a Op-Amp 741 . The op-amp is designed as voltage follower .The circuitry measures temperatures with a resolution of up to 1.0 degree Celsius. The output voltage is converted to temperature by a simple conversion factor.
Features
1. Easy interface to all microcontrollers.
2. Operates ratio metrically or with 5 VDC or analog span adjusted voltage reference.
3. No zero or full-scale adjust required.
4. 8-channel multiplexer with address logic.
5. 0V to 5V input range with single 5V power supply.
6. Outputs meet TTL voltage level specifications.
7. 28-pin molded chip carrier package
Block diagram of ADC0808:
Conversion Method Used
Following are the most used conversion methods:
i. Digital-Ramp ADC
ii. Successive Approximation ADC
iii. Flash ADC
Successive approximation ADC is suitable for the proposed application. It is much faster than the digital ramp ADC because it uses digital logic to converge on the value closest to the input voltage. A comparator and a DAC (Digital to Analog Converter) are used in the process.
General algorithm for ADC interfacing contains the following steps
1. Ensure the stability of analog input, applied to the ADC
2. Issue start of conversion SOC pulse to ADC
3. Read end of conversion EOC signal to mark the end of conversion process
Introduction Liquid Crystal Display:
A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. Each pixel consists of a column of liquid crystal molecules suspended between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. Without the liquid crystals between them, light passing through one would be blocked by the other. The liquid crystal twists the polarization of light entering one filter to allow it to pass through the other. Many microcontroller devices use 'smart LCD' displays to output visual information. LCD displays designed around Hitachi's LCD HD44780 module, are in expensive, easy to use, and it is even possible to produce a readout using the 8x80pixels of the display. They have a standard ASCII set of characters and mathematical symbols. For an 8-bit data bus, the display requires a +5V supply plus 11 I/O lines. For a 4-bitdata bus it only requires the supply lines plus seven extra lines. When the LCD display is not enabled, data lines are tri-state and they do not interfere with the operation of the microcontroller.