Sitarambhai Naranjibhai Patel Institute Of Technology & R.C

SERVO MOTOR & D.C MOTOR INTERFACING WITH ATMEGA32

servomotor working and principle What is Servo Motor?  This is nothing but a simple electrical motor, controlled with the help of servomechanism. If the motor as controlled device, associated with servomechanism is DC motor, then it is commonly known DC Servo Motor.  Servo motor is a special type of motor which is automatically operated up to certain limit for a given command with help of error-sensing feedback to correct the performance.

A servo motor is basically a DC motor(in some special cases it is AC motor) along with some other special purpose components that make a DC motor a servo. In a servo unit, we will find a small DC motor, a potentiometer, gear arrangement and an intelligent circuitry. The intelligent circuitry along with the potentiometer makes the servo to rotate according to our wishes. As we know, a small DC motor will rotate with high speed but the torque generated by its rotation will not be enough to move even a light load. This is where the gear system inside a servomechanism comes into picture.

This amplified error signal acts as the input power of the dc motor and the motor starts rotating in desired direction. As the motor shaft progresses the potentiometer knob also rotates as it is coupled with motor shaft with help of gear arrangement As the position of the potentiometer knob changes there will be an electrical signal produced at the potentiometer port. As the angular position of the potentiometer knob progresses the output or feedback signal increases. After desired angular position of motor shaft the potentiometer knob is reaches at such position the electrical signal generated in the potentiometer becomes same as of external electrical signal given to amplifier.

At this condition, there will be no output signal from the amplifier to the motor input as there is no difference between external applied signal and the signal generated at potentiometer. As the input signal to the motor is nil at that position, the motor stops rotating. This is how a simple conceptual servo motor works.

Types of servo motor Servos come in many sizes and in three basic types: positional rotation, continuous rotation, and linear.  Positional rotation servo: This is the most common type of servo motor. The output shaft rotates in about half of a circle, or 180 degrees. It has physical stops placed in the gear mechanism to prevent turning beyond these limits to protect the rotational sensor. These common servos are found in radio-controlled cars and water- and aircraft, toys, robots, and many other applications.

 Continuous rotation servo: This is quite similar to the common positional rotation servo motor, except it can turn in either direction indefinitely. The control signal, rather than setting the static position of the servo, is interpreted as the direction and speed of rotation. The range of possible commands causes the servo to rotate clockwise or counterclockwise as desired, at varying speed, depending on the command signal. You might use a servo of this type on a radar dish if you mounted one on a robot. Or you could use one as a drive motor on a mobile robot.

 Linear servo: This is also like the positional rotation servo motor described above, but with additional gears (usually a rack and pinion mechanism) to change the output from circular to back-and- forth. These servos are not easy to find, but you can sometimes find them at hobby stores where they are used as actuators in larger model airplanes.

controlling of servomotor The design of the power supply unit servo motor controller depends on the number of servo motor that are interfaced to the board. Servo motors operate from 4.8V to a 6V supply voltage. The typical value is 5v. The servo motor has three terminals. 1) Position signal (PWM Pulses) 2) Vcc (From Power Supply) 3) Ground

The servo motor angular position is controlled by applying PWM pulses of specific width. The duration of pulse varies from about 0.5 ms for 0 degree rotation to 2.2 ms for 180 degree rotation. The pulses need to be given at frequencies of about 50Hz to 60Hz. In order to generate the PWM (Pulse Width Modulation) waveform, as shown in figure below, one can use either the internal PWM module of the micro-controller or the timers can be used. Using the PWM block is more flexible as most micro- controller families design the blocks to suit the needs of application like Servo motor.

For different widths of PWM pulses, we need to program the internal registers accordingly.

servo motor interfacing with Atmega 32 Servo Motor is a DC Motor equipped with error sensing negative feedback to control the exact angular position of the shaft. Unlike DC Motors it will not rotate continuously. It is used to make angular rotations such as 0-90°, 0-180° etc. Stepper Motors can also be used for making precise angular rotations. But Servo Motors are preferred in angular motion applications like robotic arm, since controlling of servo motors are simple, needs no extra drivers like stepper motor and only angular motion is possible.

Operation of Hobby Servo Motor is very simple, it has only three wires, two of them (Red and Brown) used to provide power and the third wire is used to provide control signals. Pulse Width Modulated (PWM) waves are used as control signals and the angular position is determined by the width of the pulse at the control input. we are using a servo motor having angle of rotation from 0-180° and angular position can be controlled by varying the pulse width between 1ms to 2ms.

Inside a servo motor

The DC motor is connected with a gear mechanism which provides feedback to a position sensor which is mostly a potentiometer. From the gear box, the output of the motor is delivered via servo spline to the servo arm. The potentiometer changes position corresponding to the current position of the motor. So the change in resistance produces an equivalent change in voltage from the potentiometer. A pulse width modulated signal is fed through the control wire. The pulse width is converted into an equivalent voltage that is compared with that of signal from the potentiometer in an error amplifier.

Circuit Diagram Fig. servo motor interfacing with Atmega32

8 MHz Crystal is used to provide the required clock for Atmega32 Microcontroller. Three switch are connected to PORTB(PB0,PB1,PB2) and1.1KΩ three resistor are connected to this three switch. Control of servo motor is connected to the forth pin of PORTB (PB3), which is declared as an output pin in the program. Oscillator is connected with output of servo motor and we can seen waveform(PWM) of servo motor at different angle(0°,90°,180°).

Output (0°rotation -1ms PWM)

Waveform (1ms PWM) Fig. For [0 degree rotation (1ms PWM)]

Output (90°rotation -1.5ms PWM)

Waveform (1.5ms PWM) Fig. For [90 degree rotation (1.5ms PWM)]

Output (180°rotation -2ms PWM)

Waveform (2ms PWM) Fig. For [180 degree rotation (2ms PWM)]

Assembly Program.include "m32def.inc" LDI R18,HIGH(RAMEND) OUT SPH,R18 LDI R18,LOW(RAMEND) OUT SPL,R18 LDI R18,0XF8 // load f8 to resistor 18 OUT DDRB,R18 LDI R16,0X08 // load 08 to resistor 16 CBI PORTB,3 L1: IN R18,PINB SBRS R18,0 RCALL CASE1 SBRS R18,1 RCALL CASE2 SBRS R18,2 RCALL CASE3 RJMP L1 DELAY: LDI R20,0XC2 // load c2 to resistor 20 OUT TCNT0,R20 LDI R20,0X03 // load 03 to resistor 20 OUT TCCR0,R20 L2: IN R20,TIFR SBRS R20,TOV0 RJMP L2 LDI R20,0X00 // load 00 to resistor 20 OUT TCCR0,R20 LDI R20,(1<<TOV0) OUT TIFR,R20 RET

CASE1: LDI R16,38 SBI PORTB,3 RCALL DELAY CBI PORTB,3 L3: RCALL DELAY DEC R16 BRNE L3 RET CASE2: LDI R16,37 // load 37 to resistor 16 SBI PORTB,3 RCALL DELAY CBI PORTB,3 L4: RCALL DELAY DEC R16 BRNE L RET CASE3: LDI R16,36 // load 36 to resistor 16 SBI PORTB,3 RCALL DELAY CBI PORTB,3 L5: RCALL DELAY DEC R16 BRNE L RET

DC MOTOR WORKING AND PRINCIPLE A motor is an electrical machine which converts electrical energy into mechanical energy. The principle of working of a DC motor is that "when a current carrying conductor is placed in a magnetic field, it experiences a mechanical force". The direction of this force is given by Fleming's left hand rule and it's magnitude is given by F = magnetic flux density (B) * current (I) * length (L)

DC MOTOR Fig. d.c motor

Fleming's left hand rule: if we extend index finger, middle finger and thumb of our left hand, perpendicular to each other, and direction of magnetic field is represented by index finger, direction of current is represented by middle finger, then the thumb represents the direction of the force experienced by the current carrying conductor.

Dc motor interfacing with atmega32 we can’t connect a DC Motor directly to a microcontroller due to following reasons. A microcontroller can’t supply the current required for the working of DC Motor. ATmega32 Microcontroller can source or sink currents up to 40mA but a DC Motor needs current very much more than that. The negative voltages created due to the back emf of the motor may affect the proper functioning of the microcontroller. we may need to control the direction of rotation of the motor by changing the polarity of the motor supply.

The operating voltage of the DC Motor may be much higher than the operating voltage of the microcontroller. To solve these problems we may use an IC driver such as L293D or L293 instead of making your own H Bridge, which simplifies our project. L293D is a Quadruple Half H-Bridge driver commonly used for motor driving. We needn’t connect any transistors, resistors or freewheeling diodes.

All the four outputs of this IC are TTL compatible and output clamp diodes are provided to drive inductive loads. L293D can provide up to 600mA current, in the voltage raging from 4.5 to 36v. L293 is a similar IC which can provide up to 1A in the same voltage range. L293 or L293D contains four Half H Bridge drivers and are enabled in pairs. Input EN1 is used to enable pair 1 (IN1-OUT1, IN2-OUT2) and input EN2 is used to enable pair 2 (IN3-OUT3, IN4-OUT4). We can drive two DC Motors with one L293D,

Use of DC Motors: The most common actuator in mobile robotics simple, cheap, and easy to use. come in a great variety of sizes, to accommodate different robots and tasks.

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