Digital Tachometer Project Report

WIDE RANGE DIGITAL TACHOMETER (WRDT)

1.0

INTRODUCTION

Digital tachometer is an optical encoder that determines the angular velocity of a rotating shaft or motor. Digital tachometers are used in different applications such as automobiles, aeroplanes, and medical and instrumentation applications. The word tachometer is derived from two Greek words: tachos means “speed” and metron means “to measure”. It works on the principle of a tachometer generator, which means when a motor is operated as a generator, it produces the voltage according to the velocity of the shaft. It is also known as revolution-counter, and its operating principle can be electromagnetic, electronic or optical-based. Power, accuracy, RPM range, measurements and display are the specifications of a tachometer. Tachometers can be analogue or digital indicating meters; however, this article focuses only on the digital tachometers.

1.1 TYPES OF DIGITAL TACHOMETER Digital tachometers are classified into four types based on the data acquisition and measurement techniques.  Based on the data acquisition technique, the tachometers are of the following types: 1. Contact type 2. Non-Contact type  Based on the measurement technique, the tachometers are of the following types: 1. Time measurement 2. Frequency measurement

Fig 1.1.A: Contact type

Fig 1.1.B: Non-contact type

1

WIDE RANGE DIGITAL TACHOMETER (WRDT)

1.1.A CONTACT TYPE A tachometer which is in contact with the rotating shaft is known as contact type tachometer. This kind of tachometer is generally fixed to the machine or electric motor. An optical encoder or magnetic sensor can also be attached to this so that it measures its RPM. Digital Tachometers are capable of measuring low-speeds at 0.5 rpm and high speed at 10,000 rpm and are equipped with a storage pocket for the circumferential measurement. The specifications of this tachometer are LCD 5 digit display, operational temperature range of 0 to + 40oC, temperature storage range of – 20 to + 55o C and rotating speed of about 0.5 to 10,000 rpm. 1.1.B NON-CONTACT TYPE A tachometer that does not need any physical contact with the rotating shaft is called as noncontact digital tachometer. In this type, a laser or an optical disk is attached to the rotating shaft, and it can be read by an IR beam or laser, which is directed by the tachometer. This type of tachometer can measure from 1 to 99,999 rpm; the measurement angle is less than 120 degrees, and the tachometer has a five-digit LCD display. These types of tachometers are efficient, durable, accurate, and compact, and also visible from long distance 1.1.C TIME MEASUREMENT A tachometer that calculates the speed by measuring the time interval between incoming pulses is known as time-based digital tachometer. The resolution of this tachometer is independent of the speed of the measurement, and it is more accurate for measuring low speed. 1.1.D FREQUENCY MEASUREMENT A tachometer that calculates the speed by measuring the frequency of the pulses is called as frequency-based digital tachometer. This type of tachometer is designed by using a red LED, and the revolution of this tachometer depends on the rotating shaft, and it is more accurate for measuring high speed. These tachometers are of low-cost and high-efficiency, which is in between 1Hz-12 KHz.

The basis of our project is Non-contact type + Frequency measurement

2

WIDE RANGE DIGITAL TACHOMETER (WRDT)

1.2 OTHER PRACTICAL TACHOMETERS 1.2.A TACHOGENERATOR A micro-electric machine that is used to convert, the rotating speed and the shaft values of a machine into an electric signal is known as tachometer generator. The operation of the tachometer generator is based on the principle that the angular velocity of rotor is proportional to the generated EMF if the excitation flux is constant. These tachometers are specified with generated voltage, accuracy, maximum speed, ripples and operating temperature. This kind of tachometer generators are used as sensors in various automobile and electromechanical computer devices. The generators can be AC or DC types.

Fig 1.2.A: Tachogenerator

1.2.B ELECTRONIC TACHOMETER A tachometer made purely from electronic components and is used to measure the speed of an engine or any other moving object in revolutions per minute is known as an electronic tachometer. Electronic tachometers are used in the dashboard of a car for measuring the driving speed. These tachometers are light weight, easy to view and accurate under all conditions. They are usually not potable.

Fig 1.2.B: Electronic tachogenerator

3

WIDE RANGE DIGITAL TACHOMETER (WRDT)

1.3 INTEL FAMILY 8051 MOCROCONTROLLER The Intel MCS-51 (commonly referred to as 8051) is a Harvard architecture, CISC instruction set, single chip microcontroller (µC) series which was developed by Intel in 1980 for use in embedded systems.[1] Intel's original versions were popular in the 1980s and early 1990s and enhanced binary compatible derivatives remain popular today. Intel's original MCS-51 family was developed using NMOS technology, but later versions, identified by a letter C in their name (e.g.89C51) used CMOS technology and consume less power than their NMOS predecessors. This made them more suitable for battery-powered devices.

Fig 1.3: The original intel 8051 (aka mcs-51) chip

The family was continued in 1996 with the enhanced 8-bit MCS-151 and the 8/16/32-bit MCS-251 family of binary compatible microcontrollers.[2] While Intel no longer manufactures the MCS-51, MCS-151 and MCS-251 family, enhanced compatible derivatives made by numerous vendors remain popular today. Some derivatives integrate a digital signal processor (DSP). In addition to these physical devices, several companies also offer MCS-51 derivatives as IP cores for use in FPGAs or ASICs designs.

1.4 IR Transmitter Receiver Infrared (IR) transmitters and receivers are present in many different devices, though they are most commonly found in consumer electronics. The way this technology works is that one component flashes an infrared light in a particular pattern, which another component can pick up and translate into an instruction. These transmitters and receivers are found in remote controls and all different types of 4

WIDE RANGE DIGITAL TACHOMETER (WRDT)

devices, such as televisions and DVD players. Peripheral devices that include this technology can also allow a computer to control various other consumer electronics.

Fig 1.4: Optical Transducer

Most common consumer electronic remote controls use infrared light. They typically generate infrared using light emitting diodes (LEDs), and the main component of a receiver unit is usually a photodiode. A remote control flashes a pattern of invisible light, which is picked up and then turned into an instruction by the receiver module. The parts necessary to construct transmitter and receiver are typically inexpensive, but these systems are limited to line of sight operation. We have conceptualised this idea by replacing an IR diode with a normal LED, because IR gets reflected from all objects, while the requirement in our project is the reflection of light only from a certain surface, like a reflective one.

1.5 COMPARATOR To use operational amplifiers in open loop as comparators is quite common. This especially applies when an op amp is already used in the application, giving the user the opportunity to use a dual channel (or quad channel) op amp which can save space in the application. Thesis possible even if a better alternative is to use comparators that are optimized for this purpose. The op amp is a device which is designed to be used with negative feedback. A major concern is to ensure the stability of such a configuration.

Fig 1.5: comparator symbol and characteristics 5

WIDE RANGE DIGITAL TACHOMETER (WRDT)

Other parameters like slew rate and maximum bandwidth are trade-offs with current consumption and the architecture of an op amp. Comparators, on the other hand, are designed to operate in open loop configuration without any negative feedback. In most cases, they are not internally compensated. The speed (propagation delay) and slew rate (rise and fall time) are maximized. The overall gain is also usually higher. The use of an op amp as a comparator leads to an optimized situation, where current consumption versus speed ratio is low. The opposite is even worse. Normally, a comparator cannot be used instead of an op amp. Most probably, the comparator shows instability under negative feedback. Generally speaking, comparators and operational amplifiers cannot substitute each other except for low performance designs.

1.6 Electronic Displays Electronic Displays are electronic equipment used at the final stage of a circuit to display the output. The major types of electronic displays used are described in the following sections. 1.6.A LED Display A seven-segment display (SSD), or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information. The seven elements of the display can be lit in different combinations to represent the Arabic numerals. Often the seven segments are arranged in an oblique (slanted) arrangement, which aids readability. In most applications, the seven segments are of nearly uniform shape and size (usually elongated hexagons, though trapezoids and rectangles can also be used), though in the case of adding machines, the vertical segments are longer and more oddly shaped at the ends in an effort to further enhance the readability.

fig 1.6.A : 7 Seg LED

Types of seven segment LED Displays i)

Common Anode Display

ii)

Common Cathode Display

6

WIDE RANGE DIGITAL TACHOMETER (WRDT)

1.6.B LCD Displays A liquid crystal display is a special thin flat panel that can let light go through it, or can block the light. (Unlike an LED it does not produce its own light). The panel is made up of several blocks, and each block can be in any shape. Each block is filled with liquid crystals that can be made clear or solid, by changing the electric current to that block. Liquid crystal displays are often abbreviated LCDs.

Fig 1.6.B : LCD Display

Liquid crystal displays are often used in battery-powered devices, such as digital watches, because they use very little electricity. They are also used for flat screen TV's. Many LCDs work well by themselves when there is other light around (like in a lit room, or outside in daylight). For smartphones, computer monitor, TV's and some other purposes, a back-light is built into the product. Though LCD display could have been easily interfaced, we chose LED ahead for simplicity and compactness. Also LCD needs more stabilisation time while all you need to do is provide a delay for repeatedly showing the result due to perception of vision.

1.7 HEAT SINK In electronic systems, a heat sink is a passive heat exchanger that cools a device by dissipating heat into the surrounding medium. In computers, heat sinks are used to cool central processing units or graphics processors.

Fig 1.7: Power Transistor Heat Sink

7

WIDE RANGE DIGITAL TACHOMETER (WRDT)

A heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it, such as the air. Air velocity, choice of material, protrusion design and surface treatment are factors that affect the performance of a heat sink. Heat sink attachment methods and thermal interface materials also affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease improve the heat sink's performance by filling air gaps between the heat sink and the heat spreader on the device.

8

WIDE RANGE DIGITAL TACHOMETER (WRDT)

2.0 BLOCK DIAGRAM

Fig 2.0: Block Diagram of WRDT

9

WIDE RANGE DIGITAL TACHOMETER (WRDT)

2.1 OPTOCOUPLER An optical coupler, also called opt-isolator, optocoupler, optocoupler, photocoupler or optical isolator, is a passive optical component that can combine or split transmission data (optical power) from optical fibers. It is an electronic device which is designed to transfer electrical signals by using light waves in order to provide coupling with electrical isolation between its input and output. The main purpose of an optocoupler is to prevent rapidly changing voltages or high voltages on one side of a circuit from distorting transmissions or damaging components on the other side of the circuit. An optocoupler contains a light source often near an LED which converts electrical input signal into light, a closed optical channel and a photosensor, which detects incoming light and either modulates electric current flowing from an external power supply or generates electric energy directly. The sensor can either be a photoresistor, a silicon-controlled rectifier, a photodiode, a phototransistor or a triac.

Fig 2.1 : IR-Photo Diodes as Optocoupler

This Sensor module works on the principle of Reflection of Infrared Rays from the incident surface. A continuous beam of IR rays is emitted by the IR LED. Whenever a reflecting surface (white/obstacle) comes in front of the Receiver (photo diode), these rays are reflected back and captured. Whenever an absorbing surface (Black/No Obstacle) comes in front of the Receiver, these rays are absorbed by the surface and thus unable to be captured. FEATURES: 1) 2) 3) 4)

Active low on object detection Easy interface to connector Indicator LED Potentiometer for changing the range of detection

10

WIDE RANGE DIGITAL TACHOMETER (WRDT)

2.2 SIGNAL CONDITIONER CIRCUIT The signal conditioner circuit performs very vital role in ant electronic circuitry. Signal conditioning means manipulating the available analogue signal in such a way that it meets the requirement of the next stage of circuit for further processing. Here QUAD COMPARATOR DIP IC LM339 is used as a Schmitt trigger, this Schmitt trigger is used to convert the artery available signal into a perfect square wave to meet the need of the further frequency metre to further process The fundamental idea is as shown here-

Fig 2.2 [ Note: Single comparator is used. The IC is used as A to D convertor The comparator is used as Schmitt trigger, providing the same frequency that of the input.]

2.2.A INPUT Input is the measuring quantity. In our project input is the reflecting surface which is attached to the motor. When the rotational body rotates, the reflecting surface will repeat equal times the rotating body rotates. This reflecting surface will provide an appropriate reflected light on the surface of the optical transducer. 2.2.B OUTPUT Any system without output is of no worth. The output of our system is the speed of the rotating machine. The speed of machine is displayed in rotation per seconds. A 4 digit 7 segment display is used to show the speed count. This display is interfaced with AT89S51 microcontroller. It simply shows display count of the frequency of the number of pulses.

2.3 POWER UNIT Power is the rate of doing work. It is equivalent to an amount of energy consumed per unit time. In the SI system, the unit of power is the joule per second (J/s), known as the watt in honour of James Watt, the eighteenth-century developer of the steam engine.

11

WIDE RANGE DIGITAL TACHOMETER (WRDT)

The integral of power over time defines the work performed. Because this integral depends on the trajectory of the point of application of the force and torque, this calculation of work is said to be path dependent.

Fig 2.3: Power Unit

The same amount of work is done when carrying a load up a flight of stairs whether the person carrying it walks or runs, but more power is needed for running because the work is done in a shorter amount of time. The output power of an electric motor is the product of the torque that the motor generates and the angular velocity of its output shaft. The power involved in moving a vehicle is the product of the traction force of the wheels and the velocity of the vehicle. The rate at which a light bulb converts electrical energy into light and heat is measured in watts—the higher the wattage, the more power, or equivalently the more electrical energy is used per unit time.

2.4 SIGNAL PROCESSOR (Schmitt Trigger) As the microcontroller cannot deal with analog data (certainly the 8051), some way must be established in order to help the controller count the pusles. This job is done by the signal processor block.

Fig 2.4: Schmitt trigger characteristics 12

WIDE RANGE DIGITAL TACHOMETER (WRDT)

The signal processor not only does the job of A-D conversion, it also smoothens the waveform with a Schmitt trigger employed using comparator, and also amplifies the signal level. [Note : The comparator doesn’t amplify in reality, but it does the job of comparing to inputs (within saturation limits), assuming that input signal is quite weak¸ after comparison it gives the output either high or low (or +vsat, –vsat depending on the comparator used), so we can say that the signal is considerably amplified in other sense.]

2.5 DISPLAY DRIVER Although there are advanced and complex display driver ICs available, they increase the hardware and also the cost making the circuit bulkier. Same task can be done with the help of a simple transistor (NPN BJT) driver. Here , the base drive ( base current ) is deliberately chosen much higher than the Ib (sat) rating (available in the datasheet ) . Due to this the collector current can no longer be given as Ic = β * Ib , but by Vcc/ Rc . By choosing small value of Rc (rather appropriate), collector current can be set as required. This ultimately increases the driving capacity of the transistor.

Fig 2.4: Transistor Driver Note: 1. For other displays like lcd, the transistor driver becomes bulkier as the number Pins is more.

2.Ic should not exceed a certain value Icmax, which increases heating and may lead to thermal runaway and spoil the display as well as entire circuitry although heat sink may be present.

13

WIDE RANGE DIGITAL TACHOMETER (WRDT)

2.6 DISPLAY (7 SEGMENT LED) As the controller used is only 8-bit, the maximum data it can handle is FFH i.e. 255 decimal. Thus maximum speed in RPM that could be measure is restricted to only 255 RPM, which is a serious drawback. Thus we decided to measure speed in RPS instead of in RPM. This increased the range of angular frequency that could be measured immensely. The equivalent RPM count that could be measured comes out to be around 15K RPM, a major drawback resulted into a major advantage. This is the unique feature of our project, and thus we have named it “WIDE RANGE DIGITAL TACHOMTER (WRDT)”. One output of many test readings taken is shown below.

Fig 2.6: Circuit functioning at high frequency

14

WIDE RANGE DIGITAL TACHOMETER (WRDT)

3.0 VITAL COMPONENTS NOT MENTIONED IN THE BLOCK DIAGRAM 3.1 CRYSTAL OSCILLATOR A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits.

Fig 3.1.A Crystal Packages

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz. More than two billion crystals are manufactured annually. Although RC, LC or any other oscillatory circuit can be used, the crystal oscillator by far gives best result for Digital Sequential Circuit. . Note the 22pF capacitors shown in below figure. Circuit configuration for crystal as CLOCK

Fig 3.1.B : Crystal internal configuration

The optimum load capacitance for a given crystal is specified by the manufacturer. Printed circuit has its own stray capacitance, hence a capacitors of particular value used. Usually value of capacitors are same.

15

WIDE RANGE DIGITAL TACHOMETER (WRDT)

3.2 7805 Regulator IC 7805 is a voltage regulator integrated circuit. It is a member of 78xx series of fixed linear voltage regulator ICs. The voltage source in a circuit may have fluctuations and would not give the fixed voltage output. The voltage regulator IC maintains the output voltage at a constant value. The xx in 78xx indicates the fixed output voltage it is designed to provide. 7805 provides +5V regulated power supply. Capacitors of suitable values can be connected at input and output pins depending upon the respective voltage levels.

Fig 3.2 : 7805 Package

Pin No

Function

Name

1 2 3

Input voltage (5V-18V) Ground (0V) Regulated output; 5V (4.8V-5.2V)

Input Ground Output

IMPORTANT RATINGS: SPECIFICATION IOL(MAX) VI VDROP RR RO ISC IPK IQ REGLINE REGLOAD

DESCRIPTION MAX LOAD CURRENT RANGE OF INPUT VOLTAGE DROPOUT VOLTAGE RIPPLE REJECTION OUTPUT RESISTANCE SHORT CIRCUIT CURENT PEAK CURRENT QUISCENT CURRENT LINE REGULATION LOAD REGULATION

RATING 1A 5V – 18V 2V TYP 73 dB TYP 15mΩ 230 mA TYP 2.2 A TYP 8 mA TYP 1.6 mV (VI= 8-12V) 4.0 mV(IO= 250750mA)

16

WIDE RANGE DIGITAL TACHOMETER (WRDT)

3.3 HEAT SINK In electronic systems, a heat sink is a passive heat exchanger that cools a device by dissipating heat into the surrounding medium. In computers, heat sinks are used to cool central processing units or graphics processors.

Fig 3.3: Heat Sink mounted on 7805

A heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it, such as the air. Air velocity, choice of material, protrusion design and surface treatment are factors that affect the performance of a heat sink. Heat sink attachment methods and thermal interface materials also affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease improve the heat sink's performance by filling air gaps between the heat sink and the heat spreader on the device.

3.4 9V Battery and Connector The most common form of nine-volt battery is commonly called the transistor battery which was introduced for the early transistor radios. It has a rectangular prism shape with rounded edges and a polarized snap connector at the top. This type is commonly used in pocket radios, paintball guns, and small electronic devices. They are also used as backup power to keep the time in certain electronic clocks. This format is commonly available in primary carbon-zinc and alkaline chemistry, in primary lithium iron disulfide, and in rechargeable form in nickel-cadmium, nickel-metal hydride and lithium-ion. Mercury oxide batteries in this form have not been manufactured in many years due to their mercury content. This type is designated NEDA 1604, IEC 6F22 and "Ever Ready" type PP3 (zinc-carbon) or MN1604[1] 6LR61 (alkaline). Most nine-volt alkaline batteries are constructed of six individual 1.5V LR61 cells enclosed in a wrapper. These cells are slightly smaller than LR8D425 AAAA cells

17

WIDE RANGE DIGITAL TACHOMETER (WRDT)

and can be used in their place for some devices, even though they are 3.5 mm shorter Carbon-zinc types are made with six flat cells in a stack, enclosed in a moisture-resistant wrapper to prevent drying.

Fig 3.4: Standard 9V Battery and Battery Connector

The battery has both terminals in a snap connector on one end. The smaller circular (male) terminal is positive, and the larger hexagonal or octagonal (female) terminal is the negative contact. The connectors on the battery are the same as on the connector itself; the smaller one connects to the larger one and vice versa.[5] The same snap style connector is used on other battery types in the Power Pack (PP) series. Battery polarization is normally obvious since mechanical connection is usually only possible in one configuration. A problem with this style of connector is that it is very easy to connect two batteries together in a short circuit, which quickly discharges both batteries, generating heat and possibly a fire.[6] An advantage is that several nine-volt batteries can be connected to each other in series to provide higher voltages.

3.5 Light Emitting Diode A light-emitting diode (LED) is a two-lead semiconductor light source. It is a pn-junction diode, which emits light when activated.[4]When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.

Fig 3.5: A White bright 10mm LED

18

WIDE RANGE DIGITAL TACHOMETER (WRDT)

This effect is called electroluminescence, and the colour of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. Led is the very important part of our project .We have used 10mm bright white led in our WRDT.

3.6 CIRCUIT BOARD Although General Purpose Board can be used, it only complicates the design due a huge number of wires which makes the circuit congested. However a more professional but difficult approach involves the use of Copper Cladded PCB for the design of tracks. This is done by special technique Etching to be discussed thoroughly in section

Fig 3.6.A : Copper Cladded Board (Before Etching)

Fig 3.6.B: Etched PCB

19

WIDE RANGE DIGITAL TACHOMETER (WRDT)

4.0 POWER SUPPLY UNIT DC Power Supplies provide direct current at varying voltage and current to a device under test. These devices are useful for testing designs in real world power situations and can act as a constant battery source when testing DC devices. Power supplies come in variety of configurations and can be used for constant-voltage or constant-current. There are also units with multiple outputs so that one source can supply several outputs to the device under test. Loads are used to test the internal power supply of a unit without risking other elements of the unit.

4.1 CIRCUIT DIAGRAM

Fig 4.1: Power unit

4.2 9V BATTERY The most common form of nine-volt battery is commonly called the transistor battery which was introduced for the early transistor radios. It has a rectangular prism shape with rounded edges and a polarized snap connector at the top. This type is commonly used in pocket radios, paintball guns, and small electronic devices. They are also used as backup power to keep the time in certain electronic clocks. This format is commonly available in primary carbon-zinc and alkaline chemistry, in primary lithium iron disulphide, and in rechargeable form in nickel-cadmium, nickel-metal hydride and lithium-ion. Mercury oxide batteries in this form have not been manufactured in many years due to their mercury content. This type is designated NEDA 1604, IEC 6F22 and "Ever Ready" type PP3 (zinc-carbon) or MN1604 6LR61 (alkaline). Most nine-volt alkaline batteries are constructed of six individual 1.5V LR61 cells enclosed in a wrapper.[2] These cells are slightly smaller than LR8D425 AAAA cells and can be used in their place for some devices, even though they are 3.5 mm shorter. Carbon-zinc types are made with six flat cells in a stack, enclosed in a moisture-resistant wrapper to prevent drying. 20

WIDE RANGE DIGITAL TACHOMETER (WRDT)

Fig 4.2: Standard 9V Battery and Battery Connector

The battery has both terminals in a snap connector on one end. The smaller circular (male) terminal is positive, and the larger hexagonal or octagonal (female) terminal is the negative contact. The connectors on the battery are the same as on the connector itself; the smaller one connects to the larger one and vice versa.[5] The same snap style connector is used on other battery types in the Power Pack (PP) series. Battery polarization is normally obvious since mechanical connection is usually only possible in one configuration. A problem with this style of connector is that it is very easy to connect two batteries together in a short circuit, which quickly discharges both batteries, generating heat and possibly a fire. An advantage is that several nine-volt batteries can be connected to each other in series to provide higher voltages.

4.3 LM7805 VOLTAGE REGULATOR IC

Fig 4.3: 7805 with filtering components

We have studied the LM7805 voltage regulator IC in depth in section 3.2. It is a member of 78xx family. Similar device 79xx can be used in case negative regulated power supplies are desirable. The ratings mentioned in section 3.2 are critical to operation of the devices and thus must be paid with massive attention.

21

WIDE RANGE DIGITAL TACHOMETER (WRDT)

4.4 FILTERING ELEMENTS A filter is a device that removes unwanted signal and allows only desired signal to pass. By looking at the definition, filter may seem to be a complex circuit, but here in this case it is just a mere combination of a few capacitors. At input side to LM7805, line frequency of AC mains must be filtered with a large value capacitance as input ripple is quite large. For this a 2200uF capacitor is used which further enhanced by connecting 2 100nF capacitors in parallel which eliminate supply frequency harmonics. At the output side to LM7805, as the Ripple Rejection Ratio of IC is good as shown in the data sheet, only a small ripple is present at the output which is considerably eliminated by a parallel combination 2 100nF capacitors.

An LED can be connected with a suitable series resistor to indicate ON state of the supply to make it look more attractive.

22

WIDE RANGE DIGITAL TACHOMETER (WRDT)

5.0 SIGNAL CONDITIONER A signal conditioner is a circuit that conditions analogue signal in such a way that it can be used to drive any A to D converter or any analogue IC. Here as the pulses are only a few microvolts high, they must be conditioned to some extent. This is done with a powerful analogue amplifier called Operational Amplifier. In electronics, signal conditioning means manipulating an analogue signal in such a way that it meets the requirements of the next stage for further processing. Most common use is in analogue-to-digital converters. In control engineering applications, it is common to have a sensing stage (which consists of a sensor), a signal conditioning stage (where usually amplification of the signal is done) and a processing stage (normally carried out by an ADC and a microcontroller). Operational amplifiers (op-amps) are commonly employed to carry out the amplification of the signal in the signal conditioning stage. Signal conditioning can include amplification, filtering, converting, range matching, isolation and any other processes required to make sensor output suitable for processing after conditioning. We have used LM339 as a comparator based signal conditioner. Types of signal conditioning are listed below. 5.1 Filtering Filtering is the most common signal conditioning function, as usually not all the signal frequency spectrum contains valid data. The common example is 60 Hz AC power lines, present in most environments, which will produce noise if amplified. 5.2 Amplifying Signal amplification performs two important functions: increases the resolution of the input signal, and increases its signal-to-noise ratio.[citation needed] For example, the output of an electronic temperature sensor, which is probably in the millivolts range is probably too low for an analog-to-digital converter (ADC) to process directly. In this case it is necessary to bring the voltage level up to that required by the ADC. Commonly used amplifiers on signal on conditioning include sample and hold amplifiers, peak detectors, log amplifiers, antilog amplifiers, instrumentation amplifiers and programmable gain amplifiers.

23

WIDE RANGE DIGITAL TACHOMETER (WRDT)

5.3 Isolation Signal isolation must be used in order to pass the signal from the source to the measurement device without a physical connection: it is often used to isolate possible sources of signal perturbations. Also notable is that it is important to isolate the potentially expensive equipment used to process the signal after conditioning from the sensor. Magnetic or optic isolation can be used. Magnetic isolation transforms the signal from voltage to a magnetic field, allowing the signal to be transmitted without a physical connection (for example, using a transformer). Optic isolation takes an electronic signal and modulates it to a signal coded by light transmission (optical encoding), which is then used for input for the next stage of processing.

Fig 5.4.A: WRDT signal conditioner

Fig 5.4.B: LM339 Voltage Comparator 24

WIDE RANGE DIGITAL TACHOMETER (WRDT)

5.4 VOLTAGE COMPARATOR Perhaps the most important block in any Signal Conditioning Circuit, a voltage comparator also acts like an amplifier, waveform smoothers and also level detector. As due to reflection of light from the rotor, the photo diode undergoes continuous transitions, i.e. from ON to OFF and OFF to ON. Thus some transition loss or noise is present. This is eliminated by using a comparator which compares the photo diode OFF voltage will a reference standard non-inverting terminal voltage. The moment the photo diode conducts and sends a low pulse, comparator senses the change at the inverting terminal and changes the output abruptly Thus a much smoother waveform is obtained at the output of the comparator that is the signal conditioner of our project. The figures below illustrate this action.

. Fig 5.4.C: Distorted Input to Signal Conditioner

Fig 5.4.D: Clean and Sharp Digitalized Output Signal Conditioner

25

WIDE RANGE DIGITAL TACHOMETER (WRDT)

6.0 TIME DELAY USING IC 555 Delay can be produce with both software and hardware control, but using a simple hardware IC 555 considerably simplifies the circuit. It is widely used in monostable (one shot) mode to generate time delay. We have not used the hardware delay as it results in increasing cost, complexity in PCB design, reduces the compactness of the entire machine.

6.1 SCHEME 1 (EXTERNAL DELAY WITH 555)

Fig 6.1.A: Time Delay Circuit

Fig 6.1.B: Output Waveforms for Time Delay Circuit 26

WIDE RANGE DIGITAL TACHOMETER (WRDT)

monostable multivibrator (MMV) often called a one-shot multivibrator, is a pulse generator circuit in which the duration of the pulse is determined by the R-C network,connected externally to the 555 timer. In such a vibrator, one state of output is stable while the other is quasi-stable (unstable). For auto-triggering of output from quasi-stable state to stable state energy is stored by an externally connected capacitor C to a reference level. The time taken in storage determines the pulse width. The transition of output from stable state to quasi-stable state is accomplished by external triggering. Pin 1 is grounded. Trigger input is applied to pin 2. In quiescent condition of output this input is kept at + VCC. To obtain transition of output from stable state to quasi-stable state, a negative-going pulse of narrow width (a width smaller than expected pulse width of output waveform) and amplitude of greater than + 2/3 VCC is applied to pin 2. Output is taken from pin 3. Pin 4 is usually connected to + VCC to avoid accidental reset. Pin 5 is grounded through a 0.01 u F capacitor to avoid noise problem. Pin 6 (threshold) is shorted to pin 7. A resistor RA is connected between pins 6 and 8. At pins 7 a discharge capacitor is connected while pin 8 is connected to supply VCC.

6.2 SCHEME 2 (INTERNAL USING PRAGRAM) In an 8051 microcontroller, it requires 12 cycles of the processor clock for executing a single instruction cycle. For an 8051 microcontroller clocked by a 12MHz crystal, the time taken for executing one instruction cycle is 1µS and it is according to the equation, Time for 1 instruction cycle= 12 /12MHz = 1µS. The shortest instructions will execute in 1µS and other instructions will take 2 or more micro seconds depending up on the size of the instruction. Thus a time delay of any magnitude can be generated by looping suitable instructions a required number of time.

Fig 6.2.A: Delay using register parameters

27

WIDE RANGE DIGITAL TACHOMETER (WRDT)

Anyway, keep one thing in mind that software delay is not very accurate because we cannot exactly predict how much time it takes for executing a single instruction. Generally an instruction will be executed in the theoretical amount of time but sometimes it may advance or retard due to other reasons. Therefore it is better to use 8051 Timer for generating delay in time critical applications. However software delay routines are very easy to develop and well enough for less critical and simple applications.

Fig 6.2.B: Delay is using NOP instruction

28

WIDE RANGE DIGITAL TACHOMETER (WRDT)

7.0 ATMEL AT89S51 MICROCONTOLLER 7.1 ARCHITECTURE OVERVIEW

Fig 7.1: AT89S51 Architecture

29

WIDE RANGE DIGITAL TACHOMETER (WRDT)

7.2 Port Structures and Operation All four ports in the AT89C51 and AT89C52 are bidirectional. Each consists of a latch (Special Function Registers P0 through P3), an output driver, and an input buffer. The output drivers of Ports 0 and 2, and the input buffers of Port 0, are used in accesses to external memory. In this application, Port 0 outputs the low byte of the external memory address, time-multiplexed with the byte being written or read. Port 2 outputs the high byte of the external memory address when the address is 16 bits wide. Otherwise the Port 2 pins continue to emit the P2 SFR content. All the Port 3 pins, and two Port 1 pins (in the AT89C52) are multifunctional. The alternate functions can only be activated if the corresponding bit latch in the port SFR contains a 1. Otherwise the port pin is stuck at 0. It has less complex feature than other microprocessor.

7.3 AT89S51 PIN DIAGRAM

Fig 7.3: Pin Diagram of AT89S51

30

WIDE RANGE DIGITAL TACHOMETER (WRDT)

7.4 PIN DESCRIPTION AT89S51

Fig 7.4: Pin Description of AT89S51

31

WIDE RANGE DIGITAL TACHOMETER (WRDT)

7.5 INSTRUCTION SET AND OTHER VENDORS (8051)

Fig 7.5.A: 8051 Instruction Set

Fig 7.5.B: Famous 8051 Vendors Worldwide 32

WIDE RANGE DIGITAL TACHOMETER (WRDT)

8.0 LM339 VOLTAGE COMPARATOR 8.1 LM339 PIN DIAGRAM

Fig 8.1: LM339 Pin Diagram

8.2 LM339 DESCRIPTION These devices consist of four independent voltage comparators that are designed to operate from a single power supply over a wide range of voltages. Operation from dual supplies also is possible, as long as the difference between the two supplies is 2 V to 36 V, and VCC is at least 1.5 V more positive than the input common-mode voltage. Current drain is independent of the supply voltage. The outputs can be connected to other open-collector outputs to achieve wired-AND relationships.

33

WIDE RANGE DIGITAL TACHOMETER (WRDT)

8.3 LM339 PIN DESCRIPTION

Fig 8.3: LM339 Pin Description

8.4 WORKING A dedicated voltage comparator will generally be faster than a general-purpose comparator pressed into service as a comparator. A dedicated voltage comparator may also contain additional features such as an accurate, internal voltage reference, an adjustable hysteresis and a clock gated input. A dedicated voltage comparator chip such as LM339 is designed to interface with a digital logic interface (to a TTL or a CMOS). The output is a binary state often used to interface real world signals to digital circuitry (see analog to digital converter). If there is a fixed voltage source from, for example, a DC adjustable device in the signal path, a comparator is just the equivalent of a cascade of amplifiers. When the voltages are nearly equal, the output voltage will not fall into one of the logic levels, thus analog signals will enter the digital domain with unpredictable results. To make this range as small as possible, the amplifier cascade is high gain. The circuit consists of mainly Bipolar transistors. For very high frequencies, the input impedance of the stages is low. This reduces the saturation of the slow, large P-N junction bipolar transistors that would otherwise lead to long recovery times. Fast small Schottky diodes, like those found in binary logic designs, improve the performance significantly though the performance still lags that of circuits with amplifiers using analog signals. Slew rate has no meaning for these devices. For applications in flash ADCs the distributed signal across eight ports matches the voltage and current gain after each amplifier, and resistors then behave as level-shifters. 34

WIDE RANGE DIGITAL TACHOMETER (WRDT)

9.0 OVERALL CIRCUIT IN ACTION

Fig 9.0: Overall Circuit Diagram 35

WIDE RANGE DIGITAL TACHOMETER (WRDT)

The circuit diagram, though shown divided the into 3 individual units namely 1. Power unit 2. Signal conditioning 3. Microcontroller and Display, they are, in actuality , part of an integral unit. They share the same supply voltage +vcc = 5v and ground as shown by appropriate symbols and labels. We will see the entire system in depth now, but step by step. As the portability of tachometer is not to be sacrificed at any cost, one portable power unit must be provided. This is accomplished using a fixed 9v dc battery and a voltage regulator. But this doesn't mean that use of ac mains is of no use. Actually, one rectifier circuit followed by the same regulator (as used with the battery powered supply) and some filtering components (also used in battery powered supply). But the main aim of a designer is not to sacrifice compactness, but usage of ac mains powered supply, requires a connecting cable to be carried all the time. This is not acceptable at all, if the circuit is meant to be compact as well as portable. One big disadvantage of using battery powered supply is the frequent drainage of battery. But we have overcome this issue using proper program code to save battery and perfect switch positioning which ensure the most efficient power handling. If battery is kept properly in a dry environment, may never get drained, still continuous use of the tachometer for say 2-3 hours may need the battery to be changed. This point is again explained in Test Points (chap 15 ) Now comes the signal conditioner. It can be visualized of consisting of an input, an output and a primary signal synthesizer. The principle operation of the project is simple, detection of light reflected from a rotating body. A bright white LED emits light continuously, but how do we sense it ? It is sensed by a photodiode. The sensitivity of photodiode should high. But in some cases, we may need to reduce it. Whenever light ray reflects, it is sensed by the photo diode, which was till now turned off with collector voltage Vc = +5v approx., is turned on giving a low signal (Vc = 0v ). These low signals which are analog in nature, are used to gate the the counter of the microcontroller. However, these pulses cannot be applied directly, as microcontroller only deals with digital data, that is either 1 or 0 . This job of digitizing the analog pulses is done by a op amp comparator, texas instruments lm339.When there is no reflection of light, photo diode is off, its collector voltage is Vc = +5v or greater than the logic high threshold of the microcontroller.

36

WIDE RANGE DIGITAL TACHOMETER (WRDT)

Thus when diode is off, it sends a +5v signal to the comparator, which compares this signal at the inverting terminal with a preset signal at the non-inverting terminal, which is deliberately set such that its less than the OFF state diode voltage (around +5v) and greater than the ON state diode voltage (a few milli volts). As the comparator detects a +5v which greater than the non-inverting threshold it gives an output voltage equal to +vsat = +5v (as stated before all components share the same vcc and ground). This is nothing but the logic1 of the microcontroller. Whenever light gets reflected from the rotating body, diode conducts and the inverting terminal voltage of the comparator is less that the non-inverting terminal threshold, giving output voltage = either -vsat or 0 (depends on whether -vee is grounded or not). As we need a digital signal, -vee is set to ground. Whenever pulse is obtained, comparator gives a logic 0. This is how the comparator, which is the signal conditioner, does the job of smoothening, digitizing and amplifying (in odd sense). The output of the comparator is connected to the pin number 15 of the microcontroller. As we have used the Timer register for external event counting (i.e. pulse counting in this case), these external events must occur at the external timer 1 interrupt pin which the pin number 15 in this case. This is set automatically when we set a timer x register as a counter in the TMOD register. Note :- If timer x is set as a timer, then the event to be counted is not external, but the clock cycles which synchronize the microcontroller AT89S51.

In the TMOD register only, setting the last 2 bits of each nibble with proper combination we can use different modes. Out of 4 modes, we have used the MODE 2,8bit auto reload mode. If the counter exceeds the value of 255 (FF) , we increment a register count so that after one roll over of the TF1, if the counted pulse is 55, it means 155H pulses are counted. But this is an error as this 8 bit controller cannot be used to display a number which exceeds 255 (in fact we can display the number above 255, but it increases the complexity almost a 1000 times, and any rotating body is very less likely to be running at a speed greater than, say even a 200 RPS. One 16 bit timer is used as a counter to count the number of pulses coming out of the comparator. A comparator to work properly, must have a pull up resistor at the output pin. If you look at our circuit diagram, you will not find any. This is because port 3 of the AT89S51 (at one pin of which comparator output is given) already has internal pull up resistors. To calculate speed in RPS, the simplest way is to count the number pulses reflecting back from the rotating body for duration of 1 sec. To serve this purpose, the other timer is used as an internal delay timer. As stated before, in the TMOD register, if we reset the TMOD.7 or TMOD.2 bits (timer/counter control bits for timer 1 and 0

37

WIDE RANGE DIGITAL TACHOMETER (WRDT)

respectively), we set the respective timer in the timer delay mode. In this mode, the counter register (so called) is incremented by every clock pulse coming from the crystal which synchronizes the entire operations of the microcontroller. Out of the 4 modes, we have used the MODE1, the 16 bit counter. The delay scheme used is identical to the one used in chap 6 under the software delay scheme, except that here, instead of using a 8 bit register, we use a 16 bit timer to produce larger delay. As we need to have a 1 sec delay, using only 16 bit counter is not enough because maximum delay that can be produced with a 16 bit register with a clock of 11.0592 MHz (what we used), max delay is 1.085*10^6*65535 = 71msec. So we use another register with initial count 14H and decrement it every time TF0 rolls over, thus we get a delay of 1 sec. This is same as giving a 71 msec delay 14 times (0.071*14 = 1). Now the final and the most important task to be done is the displaying of the counted pulses. The conventional persistence strategy for 7 seg LED is used. Here we first convert the number to decimal. As this is a 8 bit controller, maximum number is 3 digit only (255 or FFH). We first divide the number by 100, and we display the quotient. We first enable the MSB digit by enabling its transistor and disable all others. Then we find out the corresponding code for a given number depending upon whether the display is Common Anode type or Common Cathode type. These codes are usually pre stored in the program memory as look up tables and accessed using base + index addressing mode. Remember we do not display the number (or character) say 1 directly, but send its 7 seg code which nothing but a bit pattern depending on which of the a-g segments need logic 1 for CK display and logic 0 for CA display. Once MSD is sent, we again set off the MSD transistor by giving a 0 base drive, we then divide remainder of the first result by 10 and again find the 7 seg code for the quotient. We now turn the middle digit transistor driver on, keeping all others off. We display the 7 seg code, wait for some time and again turn of the driver. And lastly, the remainder of the previous result is nothing but the LSD, whose 7 seg code is searched for and then sent out to corresponding digit by making that transistor driver on. Now the important question, If only one digit is getting ON at a given time, how does the display look continuous to our eyes? The answer is “Persistence of Vision”. Once the display subroutine is done, we repeat the process a number of times until a parameter in a register becomes zero. Microcontroller performs instructions almost within a microsecond, but our eyes can at max catch only 120 frames per second. However a, the display routine time is much smaller than the time for which 120 frames may last. Thus out eyes can virtually sense no change in the very fast turn ON and OFF of the display. Thus if the display routine is repeated for a finite duration, our eyes see the display as if it was a continuous one, due persistence of vision. After completion of display, controller restarts the 1 sec time delay and counter and again displays the result. This process keeps on continuing as long as power is running. Thus very fast varying speeds, which are termed as dynamic speeds can be easily measured. This is a huge bonus.

38

WIDE RANGE DIGITAL TACHOMETER (WRDT)

In this way, our project, the Wide Range Digital Tachometer (WRDT) first converts the analog pulses into digital ones, then counts them for a perfectly set 1 sec duration, and immediately displays the result, ready to count for 1 sec again. The efficiency is in the higher 95’s as will be shown in the performance graphs (chap 10).

Fig 9.1: Real time OUTPUT

39

WIDE RANGE DIGITAL TACHOMETER (WRDT)

10. TACHOMETER CALIBRATION UNIT In this chapter we will see the tachometer calibration unit. To calibrate he tachometer a rated DC shunt motor is used which is powered with a voltage supply of maximum 12v. The figure shows the physical appearance of the motor.

Fig 10.0.1: 12v DC motor (1000Rpm)

The armature and field are shunted and connected in parallel to supply voltage. The voltage supply is variable 0-12V DC power supply. Here by varying the armature voltage the speed variation in proportion is observed.

Fig 10.0.2: Circuit Diagram

Va=Armature voltage For Va=0V: Speed of motor = 0RPM = 0RPS For Va=3V: Speed of motor = 250RPM = 4 OR 5 RPS For Va=6V: Speed of motor = 500RPM = 8 OR 9 RPS For Va=9V: Speed of motor = 750RPM = 12 OR 13 RPS Speed of motor = 1000RPM = 16 OR 17 RPS

40

WIDE RANGE DIGITAL TACHOMETER (WRDT)

10.1 CIRCUIT FOR VARIABLE OUTPUT VOLTAGE The circuit uses a astable multivibrator using IC555

Fig 10.1.1: Voltage Controller Circuit

For duty cycle = 1%

For duty cycle = 75%

For duty cycle = 25%

For duty cycle = 99% 41

WIDE RANGE DIGITAL TACHOMETER (WRDT)

As the output source and sink current of IC555 is only 200mA, the output of the IC is given to the motor driving L293D which provides a high current and isolates the motor from the supply in order to prevent the supply from back EMF of the motor.

Note: As the calibration unit is only for demonstration purpose, there are many specifications (like l293d, 12v DC shunt motor etc) not covered in the report.

42

WIDE RANGE DIGITAL TACHOMETER (WRDT)

11. PERFORMANCE GRAPHS As our WRDT measure speed in RPS, to have a comparison with speeds in RPM, we have to use a multiplication of 60 in our result. The following graph displays the linearity between the two readings-one with our WRDT and other with analog tachometer used for calibration test of a 1000 RPM DC motor.

CALIBRATION TEST RELATIONSHIP BETWEEN RPM V/S RPS READINGS (MULTIPLICATION FACTOR 60)

SPPED IN RPS - WRDT

30 25 20 15 10 5 0 0

200

400

600

800

1000

1200

1400

1600

SPEED IN RPM - ANALOG TACHOMETER

Fig 11.1: Graph with MF = 60

Analog Tachometer Reading in RPM (for calibration test) – X axis 950 820 800 680 440 380

WRDT Readings in RPS – Y axis 16 14 13 12 7 6

Fig 11.2: Table for MF = 60

43

WIDE RANGE DIGITAL TACHOMETER (WRDT)

But in case of a motor or any other rotating body, operating at lower speed, a multiplication factor of 60 means that, the resolution is 60.It means that a change of 60 RPM will correspond to a change of 1 RPS. This is highly objectionable in case of such motors. However, this is not a big set-off, as we can reduce multiplication factor by increasing the number of reflecting surfaces. This increase the accuracy of low speed measurements greatly. One such instance where a 500 RPM motor was tested with a multiplication factor of 30 (two reflecting surfaces) is shown below.

CALIBRATION TEST RELATIONSHIP BETWEEN RPM V/S RPS READINGS (MULTIPLICATION FACTOR 30)

SPPED IN RPS - WRDT

25 20 15 10 5 0 0

100

200

300

400

500

600

700

SPEED IN RPM - ANALOG TACHOMETER

Fig 11.3: Graph for MF = 30

Analog Tachometer Reading in RPM (for calibration test) – X axis 600 550 500 450 400 350 300 250 200 150 100

WRDT Readings in RPS – Y axis 20 18 16 15 13 11 10 8 6 5 3

Fig 11.4: Table for MF = 30

44

WIDE RANGE DIGITAL TACHOMETER (WRDT)

12.0 PROGRAME CODING ORG 000H

MAIN:

MOV DPTR,#LUT

// moves the addres of LUT to DPTR

MOV P1,#00000000B

// Sets P1 as an output port

MOV P0,#00000000B

// Sets P0 as an output port

MOV R6,#14D SETB P3.5 MOV TMOD,#01100001B // Sets Timer1 as Mode2 counter & Timer0 as Mode timer MOV TL1,#00000000B //loads initial value to TL1 MOV TH1,#00000000B //loads initial value to TH1 SETB TR1

BACK:

// starts timer(counter) 1

MOV TH0,#00000000B //loads initial value to TH0 MOV TL0,#00000000B //loads initial value to TL0 SETB TR0

HERE:

JNB TF0,HERE

//starts timer 0 // checks for Timer 0 roll over

CLR TR0

// stops Timer0

CLR TF0

// clears Timer Flag 0

DJNZ R6,BACK CLR TR1

// stops Timer(counter)1

CLR TF0

// clears Timer Flag 0

CLR TF1

// clears Timer Flag 1

ACALL DLOOP SJMP MAIN

// Calls subroutine DLOOP for displaying the count // jumps back to the main loop 45

WIDE RANGE DIGITAL TACHOMETER (WRDT) DLOOP: BACK1:

MOV R5,#100D MOV A,TL1

// loads the current count to the accumulator

MOV B,#100D DIV AB

// isolates the first digit of the count

SETB P1.0 ACALL DISPLAY MOV P0,A

// converts the 1st digit to 7 seg pattern

// puts the pattern to Port 0

ACALL DELAY

// 1mS delay

ACALL DELAY MOV A,B MOV B,#10D DIV AB

// isolates the secong digit of the count

CLR P1.0 SETB P1.1 ACALL DISPLAY

// converts the 2nd digit to 7 seg pattern

MOV P0,A ACALL DELAY ACALL DELAY MOV A,B

// moves the last digit of the count to accumulator

CLR P1.1 SETB P1.2 ACALL DISPLAY

// converts the 3rd digit to 7 seg pattern

MOV P0,A ACALL DELAY ACALL DELAY

46

WIDE RANGE DIGITAL TACHOMETER (WRDT) CLR P1.2 DJNZ R5,BACK1

// repeats the subroutine DLOOP 100 times

RET DELAY: MOV R7,#250D

// 1mS delay

DEL1: DJNZ R7,DEL1 RET DISPLAY: MOVC A,@A+DPTR

// gets 7 seg digit drive pattern for current value In A

RET LUT:

DB 40H

// Look up table (LUT) starts here

DB 79H DB 24H DB 30H DB 19H DB 12H DB 03H DB 78H DB 00H DB 10H END

47

WIDE RANGE DIGITAL TACHOMETER (WRDT)

13.0 BURNING THE HEX CODE In order to store the software code into the controller memory, which is nothing but a flash ROM, it must be flashed with some hardware tools accompanied by some software called IDE. The software platform we used was Keil Microvision V5 and the hardware used to flash the ROM was USBASP which is a USB programmer.

13.1 BUILDING HEX FILE The following steps are involved in building the hex file: 1. Create a new Microvision Project in the project menu. Save the file with proper name. 2. Select your target microcontroller (AT89S51 in this case) and add startup files if needed. 3. Open text editor and save yourfile.asm. 4. Write down your code. 5. Add the existing file yourfile.asm to source group one in target. 6. Build target. 7. You will see hex file in the destination folder. Burn the code using USBASP.

Fig 13.1.A: Steps 1 to 4

48

WIDE RANGE DIGITAL TACHOMETER (WRDT)

Fig 13.1.B: Steps 5 to 7

Fig 13.1.C: PRPGISP program windows

Fig 13.1.D: USBASP

49

WIDE RANGE DIGITAL TACHOMETER (WRDT)

14.0 MAJOR PROCESSES INVOLVED IN FABRICATING CIRCUIT The major process involved in the fabrication of circuit are as follows:-

1 ) Etching PCB 2 ) Soldering

14.1 Etching PCB A printed circuit board mechanically supports and electrically connects electronic components using conductive tracks, pads, and other features etched from copper sheets laminated on to a nonconductive substrate. PCB can be single sided (one copper layer) , Double sided ( two copper layers ) or multi-layer conductors on different layers are connected with plated through holes called vias . Advance PCB may contain components like capacitors, resistors or active devices embedded in the substrate. Printed circuit board are used in all the simplest electronic product. Alternatives to PCBs include wire wrap and point to point construction. PCBs required the additional design effort to lay out the circuit but manufacturing circuits with PCB is cheaper and faster than with other wiring methods as components are mounted and wired with one single part. The materials required for etching PCB are as follows:1 ) Copper Cladded Board. 2 ) LASER Printer. 3 ) fine sand paper or Kitchen scrubber. 4 ) Chemicals a ) Hydrochloric Acid (HCL) b ) Ferrous chloride (Fecl3) c ) Thinner or Acetone 5 ) Electronic or Hand drill with Fine Drill Bits (0.5mm-1.2mm) 6 ) Hacksaw

50

WIDE RANGE DIGITAL TACHOMETER (WRDT)

The process of PCB etching involves :14.2.1 DESIGN After analysing the circuit diagram , The very first step for etching PCB involves designing of layout for components and there connections on the board.this is done by various softweres like ExpressPCB, Egal, etc.

Fig 14.2.1 : PCB track design using EXPRESS PCB

14.2.2 PRINT THE DESIGN A ) Selection of Paper - Selecting an appropriate paper is your first step in making a right selection. Glossy photo quality paper or even a glossy thick magazine sheet would do wonders. B ) Selection of Printer - We have used a printer to transfer the circuit diagram onto the copper board. If you are using a sharpie or a marker, go ahead with it. Set your printer to output maximum toner and printer your circuit on the glossy paper.

51

WIDE RANGE DIGITAL TACHOMETER (WRDT)

Fig 14.2.2 : Laser Print (PART A)

14.3 PREPARE BOARD AND TONER TRANSFER 14.3.A Prepare the Copper board Normal Copper board availabe at your radio shop would be good enough. Use a kitchen scrub or a fine sand paper and rub surface until you feel it is clean. DO NOT over do it. Once done, clean it with water and a clean cloth and avoid touching the surface. 14.3.B Transfer Tonner on board This step is not as complicated as the title says. Switch on your cloths iron and turn it to its highest setting. Place the printed paper over the board and start moving the iron over it for 10-15 minutes. Now drop the board into a mug of water and peel off the glossy paper. 14.3.C Etching the Board Mix Hydrochloric acid to Ferric chloride in a ratio of 2:3 and drop your copper board into it. Within 2-3 minutes you can see the copper removed from the board and tracks clearly visible.

52

WIDE RANGE DIGITAL TACHOMETER (WRDT)

14.3.D Remove Tonner Wash the etched board thoroughly in water and then use acetone or a nail polish remover and clean the surface so that the toner is removed and copper tracks are clearly visible.

14.3.E Drilling holes and Soldering Once the toner is completely removed, use a hand driller or an electronic drill and drill holes into the board to mount the components. Place the components and solder them across. You are ready with a complete professionally (almost) looking circuit board. If you have all the tools and parts in hand, the entire process takes less than an hour. Cautions:Muriatic Acid is dangerous. Hydrogen peroxide, although not dangerous, still gives your skin a burnt effect. Be careful with these solutions.

14.4 SOLDERING Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Soldering differs from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. For the efficient soldering flux is used.

Fig 14.4 : Needle type Soldering Tip

53

WIDE RANGE DIGITAL TACHOMETER (WRDT)

The purpose of flux is to facilitate the soldering process. One of the obstacles to a successful solder joint is an impurity at the site of the joint, for example, dirt, oil or oxidation. The impurities can be removed by mechanical cleaning or by chemical means, but the elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the work piece. Soldering irons have a ton of different tips, and each of them is better suited for different tasks. However, we have preferred to use a 1 mm needle tip soldering iron for efficient soldering. The fig shows the appearance of the iron tip.

54

WIDE RANGE DIGITAL TACHOMETER (WRDT)

15.0 KEY SPECIFICATIONS OF USED IC’S 15.1 AT89S51 SPECIFICATIONS SPECIFICATION DESCRIPTION VIL Input Low Voltage VIL Input High Voltage IS Power Supply Current 1/t clcl Oscillator Frequency Vcc Power supply Rpd Reset Pull-down Resistor ILI Input Leakage Current CIO Pin Capacitance VOH Output High Voltage

RATING 0.2 VCC-0.1V VCC+0.5V 6.5mA 33MHz 4.0V to 5.5V 0.3Mohm +10uA 10pF 0.75Vcc

15.2 LM339 SPECIFICATIONS SPECIFICATION DESCRIPTION VCC Power Supply Voltage VIO Input Offset Voltage IBIAS Input Bias Current IIO Input Offset Current ICC Supply Current GV Voltage Gain ISINK Output Sink Current VSAT Saturation Voltage

RATING 36V 5mVdc 250Na 5nA 2.5mA 200V/mV 16mA 400mV

15.3 LM7805 SPECIFICATIONS SPECIFICATION IOL(MAX) VI VDROP RR RO ISC IPK IQ REGLINE REGLOAD

DESCRIPTION Max Load Current Range of Input Voltages Dropout Voltage Ripple Rejection Output Resistance Short Circuit Current Peak Current Quiescent Current Line Regulation Load Regulation

RATING 1A 5V – 18V 2V TYP 73 dB TYP 15mΩ 230 mA TYP 2.2 A TYP 8 mA TYP 1.6 mV (VI= 8-12V) 4.0 mV(IO= 250750mA) 55

WIDE RANGE DIGITAL TACHOMETER (WRDT)

16. TEST POINTS After few years it may observe that the circuitry may malfunction or may not work, so if one would like to find the errors in the circuit than one can go for following testing points: 1. The very basic and first test point of the circuit is power unit. The battery which is used in power unit needs to be checked whether it is providing a appropriate voltage above 8V. If the battery fails to give the voltage equal/above 8V, replace the battery for powering the circuit properly. 2. At the output of the power unit, check whether the voltage is approximately equal to 5V. 3. To check the working of the sensor, connect the DSO across photo diode check whether the photo diode is in working state. 4. To check the working of the signal conditioning circuit, connect the DSO across the output of IC LM339 and VCC and check whether a perfect square wave is achieved. 5. To check the 7 segment display, connect the DMM across any select line (D0, D1, D2) and segments (a, b, c, d, e, f, g, decimal) 6. If all above parameters are alright, then if EPROM is used to store the programme code the technician may need to check the bit values are as per the HEX codes, in case if they are showing errors then re-program the controller as there are chances of alteration of bit values in the case of microcontroller

56

WIDE RANGE DIGITAL TACHOMETER (WRDT)

17.0 COST ESTIMATION SR.NO.

COMPONENT

Cost (Rs)

1

Circuit board ( Cu cladded ) Microcontroller ( AT89S51 )

15

2

3 4 5 6 7 8 9 10 11 12 13 14 15 16

Sockets a. Microcontroller b. Comparator 7 Seg common anode 4 Digit display

40

3 3 45

Comparator (LM339) Tx = LED Rx = Photo Diode Resisters (