# 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   of curvature 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 uncertainties and 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 not for us but for everyone. To measure the radius of curvature of a lens  —  the spherometer is levelled and read, then placed on the sphere, adjusted until the four points exert equal  pressure, and read again. It also involves huge calculation, the spherical radius  R  is given by the formula: And finding of LSD of screw gauge adds to its toughness ( ―that bounces to most of students  even in their 3 rd  year of g raduation‖) . 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 OF CURVATURE OF LENS INTERFACING 8085 MICROPROCESSOR‖.( see how this ― BABY MIND ‖  does 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    BEGINNING OF STORY……….   Block diagram giving a view of light detecting circuit      LIGHT DETECTING CIRCUIT Using opamp(351):- we used opamp as comparator .Vref is applied to pin 3 using 10k  potentiometer & 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   When no light falls on LDR the output of comparator is turned out to be -6v and when light falls on LDR 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 one  pin 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  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 a compound 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 the second one. This configuration gives a much higher current gain than each transistor taken separately

Jul 28, 2017

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Jul 28, 2017
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