A Simple Method Using Microprocessor 8085 is Suggested for the Measurement of Radius

8/12/2019 A Simple Method Using Microprocessor 8085 is Suggested for the Measurement of Radius

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ABSTRACT

A simple method using microprocessor 8085 is suggested for the measurement of radius ofcurvature of convex lens. The focal length and the radius of curvature of the convex lens can

be measured in alternate adjustments of the same set up. This method considerably reduces

requirement of long optical bench length as well as the associated bench related uncertaintiesand spherometer.

INTRODUCTION

Rightly said, Laziness of scientists leads to new findings.

Measurement of radius of curvature of lens done with spherometer is quite a big boredom notfor us but for everyone. To measure the radius of curvature of a lensthe spherometer is

levelled and read, then placed on the sphere, adjusted until the four points exert equalpressure, and read again. It also involves huge calculation, the spherical radius Ris given bythe formula:

And finding of LSD of screw gauge adds to its toughness (that bounces to most of studentseven in

their 3rdyear of graduation). Also the spherometer is costly around 34$-41$.

Keeping in view of all the difficulties we faced so far in using spherometer & make our job easier we

are introducing LEAST HUMAN INTERVENED METHOD TO MEASURE RADIUS OFCURVATURE OF LENS INTERFACING 8085 MICROPROCESSOR.(see how this BABY

MINDdoes miracle to make our job easier).

A movable light detector on a toy car is made to move along the principle axis of convex lens and

detects the focal point of convex lens , gives signal to the microprocessor to stop the motor (toy car)

and distance is calculated from convex lens to the focal point (which is done by the microprocessor).

The only calculation is 2F=R

The overall cost of project is rupees 300. Cost effective project to be looked upon and may bring

revolution in optical industry

Block diagram representing the ideology behind the project


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BEGINNING OF STORY.

Block diagram giving a view of light detecting circuit

LIGHT DETECTING CIRCUITUsing opamp(351):- we used opamp as comparator .Vref is applied to pin 3 using 10kpotentiometer & the output of potential divider circuit consisting of LDR(light dependant

resistance whose value varies according to intensity of light as, In dark=high impedence &I n

light=low impedence) and 10k resistance is given to pin 2


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When no light falls on LDR the output of comparator is turned out to be -6v and when light falls onLDR the output is +6v. this output cannot be directly read by microprocessor as it is based on TTL

technology therefore it can only read 0v to +2v as low level and 2.4v to 5v as high level. To bring the

output in desired level our next circuit comes into the picture

Half gain amplifier:- we used 741 opamp as an half gain amplifier in inverting mode. The

output of the comparator when applied to this amplifier the output changes as follows:-

In light = 3v

In dark = -3v

Now the desired range for the high level is achieved but the low level is still creating a

problem, to increase -3v to desire 0v we use a 7400 IC.

IC 7400:- The chip contains four two-input NAND gate. Each gate uses two pins for input and onepin for its output, and the remaining two contacts supply power (+5 V) and connects the ground. As

per our requirement we used two of them. First NAND gate is used as a NOT gate and output of


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amplifier is given to the input of this gate .This solved the problem of low level (0v) and high level

output (5v). The output now changed as follows-:

In light= 3.5v (high level)

In dark=200mv (low level)

But our requirement of project says high level output should come when light light falls on LDR

and low level of output when LDR is in dark. For this we used second NAND GATE as NOT GATE

to invert the output. This change the output as

In light = 200mv (low level)

In dark=3.5v(high level)

Now the mission of light detector with all the requirement is accomplished but for the motor to run

the current is not sufficient at the output of the nand gate so our next hurdle is to achieve the sufficient

currentdrive to run the motor and for this we use a darlington pair.

Darlington pair:- In electronics, the Darlington transistor(often called a Darlington pair) is acompound structure consisting of two bipolar transistors (either integrated or separated devices)

connected in such a way that the current amplified by the first transistor is amplified further by thesecond one. This configuration gives a much higher current gain than each transistor taken separately


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For transistor Q1, we have

IE1 = (1+B1)Ib1

Similarly, for 2ndtransistor we have

IE2 = (1+B2)Ib2

Since Ib2 = IE1

Therefore,

IE2 = (1+B2)IE1

= (1+B2)(1+B1)Ib1

= B1*B2*Ib1

Since, we are using the identical transistor, therefore B1=B2

Hence, IE2= (B1)2*Ib1

Where, B1=B2 = transistor current gain

So we obtained the sufficient current by using Darlington pair as current amplifier

And the output is as:-

In light = 0 amp

In dark = 3.5 milliamp

As a result of which when light falls on LDR toy car stops and in dark it starts


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Now the first section of our circuit i.e. the LDR circuit is ready to be implemented in our

project.

Now, when there is no light on LDR the output of the 1stNOT goes low and the output of 2nd

NOT goes high and TOY CAR starts to move along the principal axis of convex lens. As

soon as the TOY CAR reaches focal point of convex lens LDR senses the light(diverge at

focal point of convex lens) coming from laser source due to which output of 1stNOT goes

HIGH and 2ndNOT goes LOW hence the TOY CAR stops.

Hence focal point is detected.

Now our next objective is to calculate the distance that the TOY CAR has travelled from

convex lens to focal point.

This leads to the beginning of second sectionof project that is Distance

calculation

Distance calculator circuit

Distance calculation was the biggest hurdle that we faced in our project. Different ideas came

to our mind but at the end of the day we ended with the ever simplest method named as TIC-

TOCK TECHNIQUE

What is tic tock technique??????.....


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Two wire from 1 and 2 are suspended over the wheel of TOY CAR in such a way that when

the wheel moves 1 and 2 touches the iron pins fixed on wheels this leads to the completion of

the circuit and the output goes to +5v and when pin 1 and 2 are suspended in air (between the

two pins during the rotation of the wheel) the circuit is incomplete and output goes to 0 volt.

This process continues till the wheel rotate (like tic tock of a clock) and every time the +5comes the count is recorded on microprocessor. This phenomenon of calculation of distance

is termed as TIC-TOCK.

RADIUS OF WHEEL = 3.5cm

This implies that circumference of wheel = 2*3.14*3.5

= 21.98cm

= 22cm (approx)

We are fixed the 11 pins at the distance of 2cm each over the entire circumference of wheel.

Suppose if the number of count using TICTOCK turned out to be 22, then

The distance travelled = 22*2cm

= 44cm

Hence the formula for the distance calculation worked out to be number of counts

multiplied by2cm.

So hereby both the two sections of project are completed and can be combined together tosolve our purpose of measuring the radius of curvature.

BUT HOW??

Here comes the role of microprocessor 8085(baby mind).

When the LDR senses dark, the output of NOT GATE 2 goes HIGH and the TOY CAR starts

running and the pin 1 and 2 comes in contact with the iron pin as the wheel rotate and the

output toggle from 0 to 1 and vice versa. And whenever 1 comes, microprocessor increases a

count till the LDR reaches to the focal point of the lens. When the LDR senses the light of the

laser at the focal point, the output of the NOT GATE 1(given to PORT A of microprocessor)

goes HIGH and the output of the NOT GATE 2 goes LOW because of which TOY CAR

stops and the output of the NOT GATE 1 is used to terminate the program and the increased

count is displayed by the microprocessor.

RESULT AND OBSERVATION

CONCLUSIONThe project is successfully done. Every part of the circuit is perfectly working. The TOY

CAR is stopping at correct distance (at focal point of convex lens). The only error is due tolens adjustment and the distance between the pins fixed on the wheel. The error is turned out


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to be + 2cm or -2cm. Further the circuit can e made more compact and precise by replacinghalf gain amplifier and IC7400 with zener diode of 4.7v rating. Zener diode blocks vevoltage and gives 4.7v for +ve side. Hence serves the purpose of desired low and high leveloutput alone. There by also reducing circuitry cost.

APPENDIX

ADDRESS MNEMONICS HEX. CODE

2000 MVI B 06

2001 00 00

2002 MVI A 3E

2003 92 92

2004 OUT 03

2005 CR 03

2006 IN DB

2007 PORT A 00

2008 ANI E6

2009 O1 01

200A JNZ C2

200B 33 33200C 20 20

200D PORT B DB

200E 01 01

200F ANI E6

2010 01 01

2011 JNZ C2

2012 0D 0D

2013 20 202014 PUSH B C5


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2015 PUSH D D5

2016 PUSH H E5

2017 PUSH F F5

2018 LXI D 11

2019 00 00

201A 22 22

201B CALL CD

201C BC BC

201D 03 03

201E LXI D 11

201F 00 00

2020 55 552021 CALL CD

2022 BC BC

2023 03 03

2024 LXI H 21

2025 F6 F6

2026 27 27

2027 MOV M,B 70

2028 CALL CD2029 FA FA

202A 06 06

202B POP F F1

202C POP H E1

202D POP D D1

202E POP B C1

202F INR B 04

2030 JMP C32031 06 06

2032 20 20

2033 HLT 76


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FLOW CHART


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A Simple Method Using Microprocessor 8085 is Suggested for the Measurement of Radius