Interfacing Tower Pro SG90 9G servo motor with 8051(89c51, 89c52) Microcontroller.....

In this post i am going to teach you how to use servo motors and how to interface servo with 051 microcontroller. Microcontroller which i am using in the project is ATMEL 89c52. Servo motors are different from ordinary motors. They can rotate from 0-degree to 180-degree depending on the motor specification. Servo motors works on PWM (Pulse Width Modulation) signal. Varying pwm signal duty-cycle rotates the Arm-Head of the servo. Servo Arm-Head can rotate from 0 to 180 degree or 90 degree on each side. One can easily rotate the servo arm from 0 degree to a fixed angle and then back to 0 degree. Servo Arm-Head moving speed can also be controlled.

While going to use any servo motor first read its data sheet and look for two things

• Duty Cycle of Servo motor
• Operating Frequency or PWM Period of Servo

I am using Tower Pro Micro Servo SG90 9g. Its a small servo and weights only 9 grams. Its a power full motor and can push weight around 35 kg. Servos can push heavy loads but they can not lift heavy loads. Tower Pro can push a maximum load of 35 kg. PWM Period given for this servo motor is 20ms. Operating Frequency is 50Hz. Duty cycle is 2ms. To rotate the arm head one must have to generate a PWM Signal with signal period of 20ms and signal duty cycle in between 0 to 2ms. This Tower Pro Micro Servo SG90 9g remains at middle, right angle, 90-degree on duty cycle of 1.5ms, goes to 90-degree right, at 0-degree on 2ms duty cycle, and moves 90-degree left at duty cycle of 1ms.

One can easily rotate the arm at fixed angle by just varying the duty cycle. To rotate arm at 45-degree duty cycle will be 1.75ms. Speed of arm can be controlled by changing the duty cycle very slowly. If duty cycle increases 2 ms servo arm will not come back to its position it will go out of order. In some servo motors if the duty cycle increases the maximum limit it will have no effect on arm, those particular servos not rotate their arm on duty cycles greater than their specifications.

Tower Pro SG90 9G servo Motor Duty Cycle and PWM Period

I am going to drive four servo motors with Atmel 89c52 microcontroller. Their are four push buttons. When ever push button is pressed the corresponding servo will rotate. Servo arm will go fom 0 degree to 90 and then 180 and then back to zero. Push buttons are connected to Port-1 Pin#0,1,2,3. Servo motors are connected to Port-2 Pin#0,1,2,3.
Servo motor has theree wires coloured red,yellow,black(brown). Apply +5v to red wire. Make black(brown) ground. Apply PWM(Pulse Width modulated) signal to yellow wire.

Tower Pro SG90 9g servo motor with atmel 89c52 microcontroller.

When any push button is pressed the corresponding servo will rotate. Port-1 is declared as input port and push buttons are connected to this port. When signal is high at Port-1 pin#0,1,2,3 servos will be off. When push button is pressed corresponding pin to push button will be grounded and servo will be actuated. Port-2 is declared as output port. Servos are connected to port-2 Pin#0,1,2,3. When push button is pressed the corresponding pin on port-2 outputs a PWM signal. This pwm signal is input to servo pwm wire. This whole thing is written in the code.
 
PWM is generated using timers of 89c52 microcontroller. Timer-0 of 89c52 microcontroller is used for generating PWM signal. Now how PWM is generated using timers? To understand it you need to know what is PWM(Pulse Width Modulation).

PWM is a signal whose cycle has a high period for some time and low period for some time. It is same like digital signal which has high and low waves. In PWM the high wave of the signal is varied. This High wave is know as PWM Duty cycle.

Tower PRO SG90 9g motor has a PWM period of 20 ms. In which 18 ms is low signal and 2 ms is variable high signal. To generate delay using 89c52 microcontroller you need to calculate the values for delay and load them in the timer register. I calculated the values for generating 18 ms,1 ms,1.5,1.8 and 2ms delay and loaded them in the timer registers. TH0 and TL0 are timer registers. Here is a small tutorial link on how to calculate delay values.

• Using Timers of 89c51, 89c52 Microcontroller for generating delays.  
  

The above link is very important to understand the code. If you don't go through the above tutorial you will be unable to understand the code below. Tower Pro servo SG90 9g has duty cycle from 1 ms to 2 ms. I calculated values for these delays. Made function for each value. When ever delay is needed i call the function.

The code in while(1) function is determining whether the push button is pressed? if pressed delay functions are called. These delay fuctions are actually PWM for the motor.  

Project Code

Download the project code from the links given at the bottom of the Post.

#include< reg52.h>
void ms1();
void ms1P5();
sbit Pwm_M1=P1^0;  //Input Pin for motor Actuation
sbit Pwm_M2=P1^1;  //Input Pin for motor Actuation
sbit Pwm_M3=P1^2;  //Input Pin for motor Actuation
sbit Pwm_M4=P1^3;  //Input Pin for motor Actuation

sbit M1=P2^0;	  //Output Pin for motor Actuation (PWM output pin)
sbit M2=P2^1;	  //Output Pin for motor Actuation (PWM output pin)
sbit M3=P2^2;	  //Output Pin for motor Actuation (PWM output pin)
sbit M4=P2^3;	  //Output Pin for motor Actuation (PWM output pin)


void Pwm_Low()	  //Generating 18ms delay
{

TH0=0xBF;
TL0=0x32;
TR0=1;       //Run Timer-0
while(!TF0); //Wait for T0 Interrupt Flag
TF0=0;       //Clear Interrupt Flag
TR0=0;       //Stop Timer-0
}


void Pwm_High()		 //Generating 2ms delay
{
TH0=0xF8;
TL0=0xCC;
TR0=1;       //Run Timer-0
while(!TF0); //Wait for T0 Interrupt Flag
TF0=0;       //Clear Interrupt Flag
TR0=0;       //Stop Timer-0
}

void ms1(){             //Generating 1ms delay
TH0=0xFC;
TL0=0x65;
TR0=1;       //Run Timer-0
while(!TF0); //Wait for T0 Interrupt Flag
TF0=0;       //Clear Interrupt Flag
TR0=0;       //Stop Timer-0
}

void ms1P5(){				//Generating 1.5ms delay
TH0=0xFA;
TL0=0x99;
TR0=1;       //Run Timer-0
while(!TF0); //Wait for T0 Interrupt Flag
TF0=0;       //Clear Interrupt Flag
TR0=0;       //Stop Timer-0
}


void main()
{
unsigned int i=0;
bit status=0;
P0=0x00;  //**** Port-0 Declared Output
P1=0xFF;  //**** Port-1 Declared Input
P2=0x00;  //**** Port-2 Declared Output
P3=0x00;  //**** Port-3 Declared Output

TMOD=0x01; //Timer-0, As 16-bit Timer.

while(1){
status=((P1>>0)& 1);                       //If push button is pressed
	
	if(status==0){		  	  //Motor-1
		for(i=0;i<100;i++){	
			M1=1;
			ms1();	
			M1=0;
			Pwm_Low(); 	 }
			
		for(i=0;i<100;i++){	
			M1=1;
			ms1P5();
			M1=0;
			Pwm_Low(); 	 }

		for(i=0;i<100;i++){	
			M1=1;
			Pwm_High();		 		
			M1=0;
			Pwm_Low();	  }

		for(i=0;i<100;i++){	
			M1=1;
			ms1();	
			M1=0;
			Pwm_Low(); 	 }	  
			  			  }
						 

status=((P1>>1)& 1); 
	if(status==0){	        //Motor-2
			for(i=0;i<100;i++){	
			M2=1;
			ms1();	
			M2=0;
			Pwm_Low(); 	 }
			
		for(i=0;i<100;i++){	
			M2=1;
			ms1P5();
			M2=0;
			Pwm_Low(); 	 }

		for(i=0;i<100;i++){	
			M2=1;
			Pwm_High();		 		
			M2=0;
			Pwm_Low();	  }	
	        
		for(i=0;i<100;i++){	
			M2=1;
			ms1();	
			M2=0;
			Pwm_Low(); 	 } 

		 }	 

status=((P1>>2)& 1);
	if(status==0){		   //Motor-3
		for(i=0;i<100;i++){	
			M3=1;
			ms1();	
			M3=0;
			Pwm_Low(); 	 }
			
		for(i=0;i<100;i++){	
			M3=1;
			ms1P5();
			M3=0;
			Pwm_Low(); 	 }

		for(i=0;i<100;i++){	
			M3=1;
			Pwm_High();		 		
			M3=0;
			Pwm_Low();	  }

		for(i=0;i<100;i++){	
			M3=1;
			ms1();	
			M3=0;
			Pwm_Low(); 	 }
		 }	 

status=((P1>>3)& 1);
	if(status==0){			    //Motor-4
		for(i=0;i<100;i++){	
			M4=1;
			ms1();	
			M4=0;
			Pwm_Low(); 	 }
			
		for(i=0;i<100;i++){	
			M4=1;
			ms1P5();
			M4=0;
			Pwm_Low(); 	 }

		for(i=0;i<100;i++){	
			M4=1;
			Pwm_High();		 		
			M4=0;
			Pwm_Low();	  }			
					
		for(i=0;i<100;i++){	
			M4=1;
			ms1();	
			M4=0;
			Pwm_Low(); 	 }
			}
}
}