Post on 28-Oct-2014
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
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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
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REFERENCE
www.electronicsforyou.com
www.electroschematics.com
www.8051projects.info
www.amazon.com
www.wikipedia.com
www.google.com
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