The entire setup was placed in a cardboard box to prevent the ambient light from interfering. So the only light falling on the LDR is due to light coming from the optical fibre.

                         Fig : Experimental Setup

 

 

ARDUINO UNO REV 3 :

 

 

Overview

 

The Arduino Uno is a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; we simply have to connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.

The board has the following features:

• 1.0 pinout: added SDA and SCL pins that are near to the AREF pin and two other new pins placed near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the board. The second one is a not connected pin, that is reserved for future purposes.

• Stronger RESET circuit.

• Atmega 16U2 replace the 8U2.

Summary

Microcontroller	ATmega328
Operating Voltage	5V
Input Voltage (recommended)	7-12V
Input Voltage (limits)	6-20V
Digital I/O Pins	14 (of which 6 provide PWM output)
Analog Input Pins	6
DC Current per I/O Pin	40 mA
DC Current for 3.3V Pin	50 mA
Flash Memory	32 KB (ATmega328) of which 0.5 KB used by bootloader
SRAM	2 KB (ATmega328)
EEPROM	1 KB (ATmega328)
Clock Speed	16 MHz

 

Power

The Arduino Uno can be powered via the USB connection or with an external power supply. The power source is selected automatically.

 

Memory

The ATmega328 has 32 KB (with 0.5 KB used for the bootloader). It also has 2 KB of SRAM and 1 KB of EEPROM.

Input and Output

Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode(), digitalWrite() and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms.

The Uno has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts.

There are a couple of other pins on the board:

• AREF. Reference voltage for the analog inputs.

• Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields which block the one on the board.

 

 

WIRE BIPOLAR STEPPER MOTOR:

Stepper motors provide a means for precise positioning and speed control without the use of feedback sensors. The basic operation of a stepper motor allows the shaft to move a precise number of degrees each time a pulse of electricity is sent to the motor. Since the shaft of the motor moves only the number of degrees that it was designed for when each pulse is delivered, you can control the pulses that are sent and control the positioning and speed. The rotor of the motor produces torque from the interaction between the magnetic field in the stator and rotor. The strength of the magnetic fields is proportional to the amount of current sent to the stator and the number of turns in the windings.

 

In this experiment, we have used a stepper motor having a step angle of 1.8° and it is driven by L298 H-Bridge stepper motor driver.

 

LM 324 IC :

 

The LM324 series are low−cost, quad operational amplifiers with true differential inputs. The quad amplifier can operate at supply voltages as low as 3.0 V or as high as 32 V with quiescent currents about one−fifth of those associated with the MC1741. The common mode input range includes the negative supply, thereby eliminating the necessity for external biasing components in many applications. The output voltage range also includes the negative power supply voltage.

 

 

Features :

 

• Short Circuited Protected Outputs

• True Differential Input Stage

• Single Supply Operation: 3.0 V to 32 V

• Low Input Bias Currents: 100 nA Maximum (LM324A)

• Four Amplifiers Per Package

• Internally Compensated

• Common Mode Range Extends to Negative Supply

                                                     

                          Fig : ARDUINO - Stepper Motor-Belt System

 

 

 

 

STEPPER MOTOR-BELT SYSTEM :

 The stepper motor is driven by L298 H-Bridge stepper motor driver which gives the required power and controls the rotation of the stepper motor based on the signals generated by the ARDUINO board. The driver circuit has heat sink for better heat dissipation and flyback diodes for protection from back EMF. A flyback diode is a diode used to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply voltage is suddenly reduced or removed.

 

 

COMPARATOR CIRCUIT :

A comparator circuit was made using LM324 IC.

 

In the comparator circuit, if

·         V_LDR< V_Th => comparator’s output will be HIGH and LED will not glow.

·         V_LDR > V_Th => comparator’s output will be LOW and the LED will glow.

 

 

The comparator output voltages are always in HIGH state (≈ 10.7V) till the threshold is crossed. This voltage is used as input signal to ARDUINO. But, since the ARDUINO works for only 5V, so using voltage divider, we first stepped down the output voltage of comparator to 5V and then fed it into the ARDUINO.

 

Whenever LED glows, comparator output voltages are LOW which signals the ARDUINO to calculate the NA and the current distance L and display the same on the computer screen.

 

The outputs of  LM324 are passed through buffer so that the following LED circuit (LOAD) doesn’t affect the output voltage by drawing current.

As we move closer to the screen, the LEDs glow in the following fashion:

LED4 (blue for L=40mm) →LED3 (red) → LED2 (white) → LED1 (green for L=10mm). After LED1 glows, the average of all the four NAs are calculated and displayed and the motor reverses its rotation and the set-up is reset back to its original position of  L=50mm from the screen.