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This project has been mainly divided and implemented in the following phases:
1. Temperature Sensor
Starting with the implementation of this project, the aim of the project has been kept very clear. As the foremost requirement this project is to input the temperature of the specie environment to our designed system by some inputting device, so we need a temperature sensing device to measure the temperature readings. The specie environment can have different temperature conditions. For this purpose various temperature sensors can be used depending on our requirement. As we are designing a system which can up stand not only the normal room temperature conditions but can also measure work in extreme temperature conditions. So we need temperature sensor which has a wide range of temperature sensing abilities.
Requirements For Temperature Sensor:
- Integrated temperature sensor
- Output linear proportional to sensor readings
- Celsius (centigrade) temperature measurement.
- Low cost.
- Wide Operating range.
- Low output impedance.
- High sensitivity
- Inherent calibration
- Linear Output.
The first step in the implementation of project is use of LM 35 temperature sensor. It meets all the requirements for the system design. LM 35 reads the temperature of the specie environment and provides an output voltage at its output terminal calibrated according to Celsius temperature. The output of LM35 is an analog voltage as it can attain any continues value according to the temperature of environment. So now we need to convert this analog value to digital value.
2. Analogue To Digital Conversion
As the temperature sensor gives us an analog value, so for implementing the digital thermometer we need to go from analog world to digital world. This is the most important phase of this project. For this purpose we are required to place an analog to digital converter IC in our system. The system we are designing have 3 digit display, so we need the appropriate IC not only for analog to digital conversion but also for controlling the 3 digit display. As for a single output digit, using digital temperature logic fundamental concepts, we need 7 binary voltages. So for controlling these voltages we need at least 4 outputs from our ADC to feed a binary converter.
Requirements For ADC:
- Should accept an analog input from LM 35.
- Generate current according to input voltage.
- Convert analog voltage to 4 digital levels.
- Gain adjustability
- Sensitivity adjustment.
- Fast response.
- Generate control signal for 3 digit output.
- Low power dissipation
- Not synchronous dependent
CA3162E (ANALOG TO DIGITAL CONVERTER)
So the next step in our project was to use CA3162E A/D Converter IC. This A/D converter provides 3 digit multiplexed output. So using a BCD to seven segments IC we can control and display a digital output according to the input of this ADC. CA3162E meets all the requirements of as mentioned above and fully satisfy the need fot it to be implemented in our project.
3. BCD To Seven Segment Decoder
As up till now in our project we passed through two major phases of our system designing, but still we have not got such output which could be fed to the digital display LCD. The digital output to be displayed though LED's need seven binary outputs which control the complete display of a single digit. As the output of A/D converter is a four digit BCD, so for next step of our project we need a BCD to seven Decoder.
Requirements For Decoder:
- Constant current Segment output.
- TTL compatible Logic levels
- Low power dissipation.
- Fast conversion rate.
This phase of our project finalizes the operation on the input voltage initially got through temperature sensors. In this step we added the CA3161E BCD to seven segment decoder, so that we can fed that seven binary outputs to the digital display device. This IC meet our requirements as mentioned above for BCD to seven segment converter.
4. Digital Display
In the last phase of our project we need to display the readings we got through all the phases of our system. For this purpose we need 3 digital displays. As we have got seven segment voltages from decoder, and 3 control signals from A/D converter IC. So the last phase needs only 3 digital identifiers.
As we had 4 inputs from ADC, so using a seven segment converter IC the 4 digit BCD is converted to seven segments digit, through which we can run LED's, which will change according to the different temperature readings measured by the temperature sensor.
So all the phases of our system for digital thermometer are combined and shown in the figure below: