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Electronic Thermometer For Beverage Temperature

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ABSTRACT

This paper presents the design of an electronic thermometer for beverage temperatures. The thermometer displays the temperature of the beverage. In this work, the results are based on temperature using a temperature sensor to sense the beverage temperature. The received information from the sensor is analogue so it is converted to digital by the ADC and finally displayed on a seven-segment display. A 5V DC power supply was designed to power the circuit. The testing and simulation of the circuit design was done in Proteus 8 Professional.

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0 INTRODUCTION

1 BACKGROUND

Definitions

Beverage is a drink other than water, examples: tea, milk, juice, beer etc.

Thermometer an instrument for measuring and indicating temperature.

Digital thermometer is a resistive thermal device that predict temperature as a function of electrical resistance. In the past thermometers were made of mercury/alcohol, when either liquid senses heat it expands and fills the tube.

Even though the thermometer was effective, the reading had parallax error from different users thus the need for electronic thermometer that displays the sensed temperature. Most electronic thermometers use micro controllers and Arduino. Microcontrollers need to be programmed so that the information from the sensor can be displayed.

This project focuses on electronic thermometer using analog signal, the analog signal is further converted to a digital signal to display it on the seven-segment display.

2 MOTIVATION

Everywhere there is consumption of beverages, babies take milk, adults take tea etc but they never know the temperature of their beverages. In a case of babies, a mother needs to know if the milk is hot to avoid burning the kids’ tongue. This has become an irritating issue to individuals.

3 PROBLEM STATEMENT

Consuming up to around 50 degree Celsius cannot cause any harm. Anything hotter than that can cause harm to tissues in the mouth. The same applies to cold beverages down to 3 degree Celsius. Therefore, there is a need for a device that can indicate the temperature before taking a beverage.

4 MAIN OBJECTIVE

To design an electronic thermometer for beverage temperatures

1 OBJECTIVES

Find out the temperature sensor with higher range

Find out the ADC that can drive a seven-segment display and use it for the design for displaying

0 LITERATURE REVIEW

Temperature Sensors for Beverage

Tools and devices are typically chosen due to their accuracy, compatibility with their operating conditions, durability. When it comes beverages there are the added concerns of the need to meet sanitation standards. This is to prevent harmful contamination of beverages in order to avoid illness.

It is important to check temperature of beverages as a small variation can mean difference between a safe product or contaminated one or it may mean the beverage is likely to damage mouth tissues. Below is an example of temperature sensor that some factories use for sensing beverage temperature.

In this project, LM35 was used because it is good for experimental purposes also, it safe to be used in beverages as it can be insulated. Furthermore, it has temperature range of -50° and 150°, it does not require external calibration.

Electronic Thermometer using CA3162, CA3161 and LM35

In this circuit the voltage proportional to the sensed temperature enters the CA3162 (ADC), the ADC does its converting function of converting analogue to BCD digit. The converted data is then transmitted to the seven-segment decoder. For this function a CA3161 is used and the information is displayed on a seven-segment display.

In this paper, TC7107 was used. This an ADC with an internal circuitry for a seven-segment decoder so it converts analogue to BCD digit and drives a seven-segment display. Reason being the lesser the components the lesser the complexity of the circuit.

0 MATERIALS

The electronic thermometer for beverage temperature comprises of 3 main subsystems: the power supply unit, the sensor unit and the ADC unit (TC7107). The output is displayed on a seven-segment display.

POWER SUPPLY

The power supply system supplies a 5V DC power to other units, which is stepped down with a transformer. The power supply includes a full wave rectifier which convers AC to DC and a capacitor to smoothen the output from the rectifier. The voltage regulator was included in order to supply the regulated DC voltage to the other main units.

SENSING UNIT

This section includes a temperature sensor (LM35). A temperature sensor is a device that is temperature sensitive, and it responds to temperature changes. The LM35 senses the beverag00temperature and converts it to electrical signal. The LM35 has a large range, that should be enough for various temperatures of beverages. In this circuit the LM35 senses the temperature and it is displayed on a seven-segment display.

ADC UNIT

The TC7107A (40 PINS) is a high-performance ADC. The IC has internal circuitry for seven segment display decoders. The display stability of the IC is high.

0 DESIGN AND IMPLEMENTATION

Power supply: all components operate at 5V DC, hence the need to step down the power supply voltage from the mains (240V AC) to a reasonably voltage that will be converted to DC (rectified) and further filter to remove unwanted pulsation. The 240V was stepped down to 12V AC (with a peak-peak voltage a 17V, 20:1) as shown in the circuit below, and the 17V was further regulated to 5V.

CALCULATIONS

N_P V_s=N_s V_p

V_RMS=V_s=240/12=12V

V_P=12√2≈17V

Assuming a ripple voltage of 20%;

dv=20/100×17=3.4V

df=1/2f=1/(2×50)=0.01

C_1=0.01/3.4=2.94mF

A preferred value of 470µF was however used to for filtering of the assumed ripples as the value is much lower than the calculated one hence it will filter more than expected.

SENSING UNIT

The output voltage of the LM35 sensor (V_out)

V_out=(T°c)/100

ADC UNIT: The voltage (due to temperature change) to be measured is converted into a digital equivalent by the ADC inside the IC and then this digital equivalent is decoded to the seven-segment format and then displayed. (An integrating ADC is a type that converts an unknown input voltage into a digital representation through the use of an integrator.)

The resistor R4 and C4 are used to set the frequency of IC’s internal clock. The frequency is per section

f/3=1/2πRC=1/(2π*100kΩ*100pF)≈16kHz

f=48kHz

Capacitor C3 neutralizes the fluctuations in the internal reference voltage and increases the stability of the display.

0 RESULTS AND DISCUSSION

The process taking place inside our ADC (TC7107) can be stated as follows:

Voltage (proportional to temperature) to be measured is integrated to obtain a ramp at the output of the integrator.

Then a known reference voltage of opposite polarity is applied to the input of the integrator and allowed to ramp until the output of integrator becomes zero. The time taken for the negative slope to reach zero is measured in terms of the IC’s clock cycle and it will be proportional to the voltage being measured.

Table 5.0: showing functions of TC7107 pins

Pin Number

(40-Pin PDIP)

Normal Symbol Description

2 D1 Activates the D section of the units display.

3 C1 Activates the C section of the units display.

4 B1 Activates the B section of the units display.

5 A1 Activates the A section of the units display.

6 F1 Activates the F section of the units display.

7 G1 Activates the G section of the units display.

8 E1 Activates the E section of the units display.

9 D2 Activates the D section of the tens display.

10 C2 Activates the C section of the tens display.

11 B2 Activates the B section of the tens display.

12 A2 Activates the A section of the tens display.

13 F2 Activates the F section of the tens display.

14 E2 Activates the E section of the tens display.

15 D3 Activates the D section of the hundreds display.

16 B3 Activates the B section of the hundreds display.

17 F3 Activates the F section of the hundreds display.

18 E3 Activates the E section of the hundreds display.

21 GND Digital Ground

22 G3 Activates the G section of the hundreds display.

23 A3 Activates the A section of the hundreds display.

24 C3 Activates the C section of the hundreds display.

25 G2 Activates the G section of the tens display.

26 V- Negative power supply voltage.

27 VINT Integrator output. Connection point for integration capacitor.

28 VBUFF Integration resistor connection. The integrator and buffer can supply 20 µA drive currents with negligible linearity errors. R is used to remain in the output stage linear drive region.

29 CAZ The size of the auto-zero capacitor influences system noise.

30 VIN- The analogue LOW input is connected to this pin.

31 VIN+ The analogue HIGH input signal is connected to this pin.

32 ANALOG

COMMON This pin is primarily used to set the Analog Common mode voltage for battery

operation or in systems where the input signal is referenced to the power supply. It

also acts as a reference voltage source.

34 CREF+ A 0.1 µF capacitor is used in most applications. If a large Common mode voltage

exists (for example, the VIN- pin is not at analogue common), and a 200-mV scale is

used, a 1 µF capacitor is recommended and will hold the rollover error to 0.5 count.

35 VREF- Ground.

36 VREF+ The analogue input required to generate a full-scale output

40 OSC1 Pins 40, 39, 38 make up the oscillator section. For a 48 kHz clock (3 readings per

section), connect Pin 40 to the junction of a 100kΩ resistor and a 100-pF capacitor.

The 100kΩ resistor is tied to Pin 39 and the 100-pF capacitor is tied to Pin 38.

0 CONCLUSION

The aim of this project is to design and simulate an Electronic Thermometer for Beverage Temperature. The system uses LM35 as the temperature sensor and TC710 (ADC) that drives the 7-segment display. The output varies with the sensed temperature. This is exceptionally helpful to everyone consumes beverages and would like to know the temperature of what they are consuming. It can be used in homes, coffee shops. The design was done with Proteus and Multism software.

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