CHAPTER 1 INTRODUCTION

A digital thermometer is used to measure the atmospheric temperature.EThe digital -

thermometer can measure temperatures up to 150°C with an accuracy of ±1°C.1 The

temperature is read on a 1V full scale-deflection (FSD) moving-coil voltmeter or digital

voltmeter.

Operational amplifier IC 741 (IC3) provides a constant flow of current through the

base-emitter junction of npn transistor BC108 (T1). The voltage across the base-emitter

junction of the transistor is proportional to its temperature. The transistor used this way

makes a low-cost sensor. You can use silicon diode instead of transistor. The small variation

in voltage across the base-emitter junction is amplified by second operational amplifier

(IC4), before the temperature is displayed on the meter. Preset VR1 is used to set the zero-

reading on the meter and preset VR2 is used to set the range of temperature measurement.

Operational amplifiers IC3 and IC4 operate off regulated ±5V power supply, which is

derived from 3-terminal positive voltage regulator IC 7805 (IC1) and negative low-dropout

regulator IC 7660 (IC2). The entire circuit works off a 9V battery. Assemble the circuit on a

general-purpose PCB and enclose in a small plastic box. Calibrate the thermometer using

presets VR1 and VR2. After calibration, keep the box in the vicinity of the object whose

temperature is to be measured.

Operational amplifier IC 741 (IC3) provides a constant flow of current through the

base-emitter junction of NPN transistor BC108 (T1). The voltage across the base-emitter

junction of the transistor is proportional to its temperature. The transistor used this way

makes a low-cost sensor. we can use silicon diode instead of transistor. The small variation

in voltage across the base-emitter junction is amplified by second operational amplifier

(IC4), before the temperature is displayed on the meter. Preset VR1 is used to set the zero-

reading on the meter and preset VR2 is used to set the range of temperature measurement.

Operational amplifiers IC3 and IC4 operate off regulated +_5V power supply, which is

derived from 3-terminal positive voltage regulator IC 7805 (IC1) and negative low-dropout

regulator IC 7660 (IC2). The entire circuit works off a 9V battery.

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Assemble the circuit on a general-purpose PCB and enclose in a small plastic box.

Calibrate the thermometer using presets VR1 and VR2. After calibration, keep the box in

the vicinity of the object whose temperature is to be measured. 

1.1 Circuit Diagram:-

Figure 1.1:- Project Circuit Diagram

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1.2 Component list:-

Component Value Quantity

Resistance

R1 100 ohm 1

R2,R3 10 K ohm 1,1

VR1 100K ohm 1

VR2 500k 1

Capacitors

C1 220nf 1

C2,C3 10µf 1,11

C4 1µf 1

IC’S

IC1,IC2 741 2

IC 3 7660 1

IC 4 7805 1

Table 1.1:- Table of Components Required

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CHAPTER 2

IC-7805

The MC78XX/LM78XX/MC78XXA series of three terminal positive regulators are

available in the TO-220/D-PAK package and with several fixed output voltages, making

them useful in a wide range of applications. Each type employs internal current limiting,

thermal shut down and safe operating area protection, making it essentially indestructible. If

adequate heat sinking is provided, they can deliver over 1A output current. Although

designed primarily as fixed voltage regulators, these devices can be used with external

components to .Obtain adjustable voltages and currents.

2.1 Pin Diagram:-

Figure2.1:- Pin diagram of 7805 IC

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2.2 Data Sheet:-

Table 2.1:- Data Sheet of IC 78052.3 Note:-

Load and line regulation are specified at constant junction temperature. Changes in Vo due

to heating effects must be taken into account separately. Pulse testing with low duty is used.

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2.4 Internal Block Diagram of IC 7805:-

Figure 2.2:-Internal Block Diagram of IC 7805

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CHAPTER 3

IC 741 (OPERATIONAL AMPLIFIER)

The term operational amplifier or "op-amp" refers to a class of high-gain DC coupled

appliers with two inputs and a single output. The modern integrated circuit version is

typeset by the famous 741 op-amp. Some of the general characteristics of the IC version

are:

_ High gain, on the order of a million

_ High input impedance, low output impedance

_ Used with split supply, usually +/- 15V

_ Used with feedback, with gain determined by the feedback network.

The operational amplifier (op-amp) was designed to perform mathematical operations.

Although Now superseded by the digital computer, op-amps are a common feature of

modern analog electronics. The op-amp is constructed from several transistor stages, which

commonly include a differential input Stage, an intermediate-gain stage and a push-pull

output stage. The deferential amplifier Consists of a matched pair of bipolar transistors or

FETs. The push-pull amplifier transmits a large Current to the load and hence has a small

output impedance. The op-amp is a linear amplifier with Vout / Vinp. The DC open-loop

voltage gain of a typical op-amp is 103 to 106. The gain is so large that most often feedback

is used to obtain a specific transfer function and control the stability. Cheap IC versions of

operational appliers are readily available, making their use popular in any analog circuit.

The cheap models operate from DC to about 20 kHz, while the high-performance models

operate up to 50 MHz. A popular device is the 741 op-amp. It is usually available as an IC

in an 8-pin dual, in-line package (DIP).

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3.1 Circuit symbol:-

Figure 3.1:- Circuit symbol and DIP circuit of IC 741

3.2 Inverting and non-inverting amplifier:-

Basic circuits for inverting and non-inverting amplifier are schematically shown in Fig. 2.

The gain of the inverting amplifier is simply given by..

and the gain of the non-inverting amplifier is given by..

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Figure 3.2:- Circuit for inverting and non-inverting amplifier

3.3 Offset voltage:-

A practical concern for op-amp performance is voltage offset. That is, effect of having the

output voltage something other than zero volts when the two input terminals are shorted

together. Remember that operational appliers are deferential appliers above all: they're

supposed to amplify the deference in voltage between the two input connections and

nothing more. When that input voltage deference is exactly zero volts, we would (ideally)

expect to have exactly zero volts present on the output. However, in the real world this

rarely happens. Even if the op-amp in question has zero common-mode gain, the output

voltage may not be at zero when both inputs are shorted together. This deviation from zero

is called offset. A perfect op-amp would output exactly zero volts with both its inputs

shorted together and grounded. However, most op-amps of the shelf will drive their outputs

to a saturated level, either negative or positive.

Offset voltage will tend to introduce slight errors in any op-amp circuit. So how do we

compensate for it? There are usually provisions made by the manufacturer to trim the offset

of a packaged pomp. Usually, two extra terminals on the op-amp package are reserved for

connecting an external potentiometer. These connection points are labeled offset null.

3.4 Input bias current:-

Inputs on an op-amp have extremely high input impedances. That is, the input currents

entering or exiting an op-amp's two input signal connections are extremely small. For most

purposes of op-amp circuit analysis, we treat them as though they don't exist at all. We

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analyze the circuit as though there was absolutely zero current entering or exiting the input

connections. This idyllic picture, however, is not entirely true. Op-amps, especially those

op-amps with bipolar transistor inputs, have to have some amount of current through their

input connections in order for their internal circuits to be properly biased. These currents,

logically, are called bias currents. Under certain conditions, op-amp bias currents may be

problematic. The following circuit illustrates one of those problem conditions: Another way

input bias currents may cause trouble is by dropping unwanted voltages across circuit

resistances. Take this circuit for example:

Figure 3.3:- Calculation of Bias Current with IC 741

We expect a voltage follower circuit such as the one above to reproduce the input voltage

precisely at the output. But what about the resistance in series with the input voltage source?

If there is any bias current through the non inverting (+) input at all, it will drop some

voltage across Rin, thus making the voltage at the non inverting input unequal to the actual

Vin value. Bias currents are usually in the micro amp range, so the voltage drop across Rin

won't be very much, unless Rin is very large.

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3.5 Measurement of input bias current:-

As mentioned earlier, input bias current is very small in magnitude - so, measuring it

directly is not a good idea. However, it can be measured cleverly using the following

circuit.

Figure 3.4:- Circuits to measure input bias currents Ib1 and Ib2

Fig. 3.4(a) is just the circuit for an inverting amplifier, with the input grounded. So, the

voltage at the inverting input terminal should be ideally zero. But from the circuit above,

one can see that the voltage at the inverting input has two contributions - one, Vout reduced

by the potential divider made out of Ra and Rb, i.e., Rb Ra+Rb Vout - two, the voltage drop

over the R1 if there is a non-zero input bias current owing. Thus, we can write

If Ra = 10 k, Rb = 780 and R1 = 1 M, we get

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Input bias current Ib2 can be similarly measured using the circuit in Fig. 3(b), which

represents a non-inverting amplifier, with the input grounded through the resistor R2. The

voltage at the non-inverting terminal would be Ib2R2, which gets amplified to give Vout.

Using the relation for non-inverting gain, one can write

3.6 Op-amp as integrator and differentiator:-

Figure 3.5:- integrator

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Figure 3.6:-differentiator

In the case of an integrator, the output voltage will be

Various kinds of input waves can be given as input. The rectangular wave, for example, will produce the following output:

Figure 3.7:-Output and Input Waveforms of a Integrator

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CHAPTER 4 IC 7660 (NEGATIVE VOLTAGE REGULATOR IC)

The MAX1044 and ICL7660 is monolithic, CMOS switched-capacitor voltage converters

that invert, double, divide, or multiply a positive input voltage. They are pin compatible

with the industry-standard ICL7660 and LTC1044. Operation is guaranteed from 1.5V to

10V with no external diode over the full temperature range. They deliver 10mA with a 0.5V

output drop. The MAX1044 has a BOOST pin that raises the oscillator frequency above the

audio band and reduces external capacitor size requirements. The MAX1044/ICL7660

combines low quiescent current and high efficiency. Oscillator control circuitry and four

power MOSFET switches are included on-chip. Applications include generating a -5V

supply from a +5V logic supply to power analog circuitry. For applications requiring more

power, the MAX660 delivers up to 100mA with a voltage drop of less than 0.65V.

4.1 Typical circuit description:-

Figure 4.1:- IC 7660

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Figure 4.2:-pin configuration of IC 7660

4.2 APPLICATION OF 7660 VOLTAGE REGULATED IC:-

-5V Supply from +5V Logic Supply

Personal Communications Equipment

Portable Telephones

Op-Amp Power Supplies

EIA/TIA-232E and EIA/TIA-562 Power Supplies

Data-Acquisition Systems

Hand-Held Instruments

Panel Meters

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4.3 FEATURES OF IC 7660:-

Miniature μMAX Package

1.5V to 10.0V Operating Supply Voltage Range

98% Typical Power-Conversion Efficiency

Invert, Double, Divide, or Multiply Input Voltages

BOOST Pin Increases Switching Frequencies (MAX1044)

No-Load Supply Current: 200μA Max at 5V

No External Diode Required for Higher-Voltage Operation.

4.4 ORDERING INFORMATION:-

Table 4.1:- Ordering Information of IC 7660

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4.5 ELECTRICAL CHARACTERISTIC OF IC 7660:-

Table 4.2:- ELECTRICAL CHARACTERISTIC OF IC 7660

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4.6 PIN DESCRIPTION:-

Table 4.3:- Pin Description of IC 7660

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CHAPTER 5

ZENER DIODE

A zener diode is a special kind of diode which allows current to flow in the forward

direction in the same manner as an ideal diode, but will also permit it to flow in the

reverse direction when the voltage is above a certain value known as the breakdown

voltage, "zener knee voltage" or "zener voltage." The device was named after

Clarence Zener, who discovered this electrical property. Many diodes described as

"zener" diodes rely instead on avalanche breakdown as the mechanism. Both types

are used. Common applications include providing a reference voltage for voltage

regulators, or to protect other semiconductor devices from momentary voltage

Figure 5.1:- Zener diode

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Figure 5.2:- Output characteristics of zener diode

5.1 Operation of Zener Diode:-

A conventional solid-state diode will not allow significant current if it is reverse-biased

below its reverse breakdown voltage. When the reverse bias breakdown voltage is

exceeded, a conventional diode is subject to high current due to avalanche breakdown.

Unless this current is limited by circuitry, the diode will be permanently damaged due to

overheating. A zener diode exhibits almost the same properties, except the device is

specially designed so as to have a greatly reduced breakdown voltage, the so-called zener

voltage. By contrast with the conventional device, a reverse-biased zener diode will exhibit

a controlled breakdown and allow the current to keep the voltage across the zener diode

close to the zener breakdown voltage.

For example, a diode with a zener breakdown voltage of 3.2 V will exhibit a voltage drop

of very nearly 3.2 V across a wide range of reverse currents. The zener diode is therefore

ideal for applications such as the generation of a reference voltage (e.g. for an amplifier

stage), or as a voltage stabilizer for low- applications. Current another mechanism that

produces a similar effect is the avalanche effect as in the avalanche diode. The two types of

diode are in fact constructed the same way and both effects are present in diodes of this

type. In silicon diodes up to about 5.6 volts, the zener effect is the predominant effect and

shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect

becomes predominant and exhibits a positive temperature coefficient. In a 5.6 V diode, the

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two effects occur together and their temperature coefficients nearly cancel each other out,

thus the 5.6 V diode is the component of choice in temperature-critical applications.

Modern manufacturing techniques have produced devices with voltages lower than 5.6 V

with negligible temperature coefficients, but as higher voltage devices are encountered, the

temperature coefficient rises dramatically. A 75 V diode has 10 times the coefficient of a 12

V diode.

All such diodes, regardless of breakdown voltage, are usually marketed under the umbrella

term of "zener diode".

5.2 Construction of Zener Diode:-

The zener diode's operation depends on the heavy doping of its p-n junction. The depletion

region formed in the diode is very thin (<0.000001 m)and the electric field is consequently

very high (about 500000V/m) even for a small reverse bias voltage of about 5V, allowing

electrons to tunnel from the valence band of the p-type material to the conduction band of

the n-type material.

In the atomic scale, this tunneling corresponds to the transport of valence band electrons

into the empty conduction band states; as a result of the reduced barrier between these

bands and high electric fields that are induced due to the relatively high levels of doping on

both sides. The breakdown voltage can be controlled quite accurately in the doping process.

While tolerances within 0.05% are available, the most widely used tolerances are 5% and

10%. Breakdown voltage for commonly available zener diodes can vary widely from 1.2

volts to 200 volts.

In the case of a large forward bias (current in the direction of the arrow), the diode exhibits

a voltage drop due to its junction built-in voltage and internal resistance. The amount of the

voltage drop depends on the semiconductor material and the doping concentrations.

5.3 Uses of Zener Diode:-Zener diodes are widely used as voltage references and as shunt regulators to regulate the

voltage across small circuits. When connected in parallel with a variable voltage source so

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that it is reverse biased, a zener diode conducts when the voltage reaches the diode's reverse

breakdown voltage. From that point on, the relatively low impedance of the diode keeps the

voltage across the diode at that value.

Figure 5.3:- Symbol of Zener Diode

Figure 5.4:- Circuit Symbol of Zener Diode

In this circuit, a typical voltage reference or regulator, an input voltage, U IN, is regulated

down to a stable output voltage UOUT. The breakdown voltage of diode D is stable over a

wide current range and holds UOUT relatively constant even though the input voltage may

fluctuate over a fairly wide range. Because of the low impedance of the diode when

operated like this, resistor R is used to limit current through the circuit.

In the case of this simple reference, the current flowing in the diode is determined using

Ohm's law and the known voltage drop across the resistor R. IDiode = (UIN - UOUT) / RΩ

The value of R must satisfy two conditions:

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1. R must be small enough that the current through D keeps D in reverse breakdown.

The value of this current is given in the data sheet for D. For example, the common

BZX79C5V6 device, a 5.6 V 0.5 W zener diode, has a recommended reverse current

of 5 mA. If insufficient current exists through D, then UOUT will be unregulated, and

less than the nominal breakdown voltage (this differs to voltage regulator tubes

where the output voltage will be higher than nominal and could rise as high as UIN).

When calculating R, allowance must be made for any current through the external

load, not shown in this diagram, connected across UOUT.

2. R must be large enough that the current through D does not destroy the device. If the

current through D is ID, its breakdown voltage VB and its maximum power

dissipation PMAX, then .

A load may be placed across the diode in this reference circuit, and as long as the

zener stays in reverse breakdown, the diode will provide a stable voltage source to

the load. Zener diodes in this configuration are often used as stable references for

more advanced voltage regulator circuits.

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CHAPTER 6

TRANSISTOR BC108

Figure 6.1:- Symbol of Transistor BC108

Table 6.1:- Pinning Table of Transistor BC108

6.1 Features:- · Low current (max. 100 mA) · Low voltage (max. 45 V).

6.2 Applications:-

· General purpose switching and amplification

6.3 Life Support Applications:-

These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Philips customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Philips for any damages resulting from such improper use or sale

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6.4 Quick Reference Data for Transistor BC108:-

Table 6.2:- Quick Reference Data for Transistor BC108

6.5 Limiting Values:-

Table 6.3:- Limiting Values of Transistor BC108

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6.6 Characteristics:-

Table 6.4:- Characteristics of Transistor BC108

26

6.7 Package Outline of transistor BC108:-

Figure 6.2:- Package Outline of transistor BC108

Table 6.5:- Dimensions

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CONCLUSION

A sensor based digital thermometer is implemented using the sensor Transistor BC108.

Output of this sensor changes according to change in the Temperature surrounding

environment of this sensor. Conventional thermometers like mercury Thermometers are not

precise and accurate to calculate temperature. So this digital type thermometer gives the

temperature in digital form directly after calibrating the output voltage in temperature form.

This Thermometer is a low power Digital Thermometer works on only 9V dc supply. Cost

of this device is Rs. 255 only. It is a compact and reliable device for handling. A digital

thermometer is used to measure the atmospheric temperature. The digital thermometer can

measure temperatures up to 150°C with an accuracy of ±1°C.1 The temperature is read on a

1V full scale-deflection (FSD) moving-coil voltmeter or digital voltmeter. Operational

amplifier IC 741 (IC3) provides a constant flow of current through the base-emitter junction

of NPN transistor BC108 (T1). The voltage across the base-emitter junction of the transistor

is proportional to its temperature. The transistor used this way makes a low-cost sensor

28

REFERENCE

www.electronicsforyou.com

www.electroschematics.com

www.8051projects.info

www.amazon.com

www.wikipedia.com

www.google.com

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