How to Control a Servo Motor Using AVR ATmega16 Mini Development Board
Servos have simple electrical interface – they have 3 wires, one for power, one for ground and the other for the pulse train. Once the servo is powered, the signal wire is ready to receive signal in the form of pulse width modulation (PWM) from an external source.
The signal expects to be updated every 20 ms with a pulse between 0.5ms and 2.5ms. With a 1.5 ms pulse, the servo motor will be at the natural 90° position. With a 0.5 ms pulse, the servo will be at the 0° position, and with a 2.5 ms pulse, the servo will be at 180°. You can obtain the full range of motion by updating the servo with a value in between.
AVR ATmega16 mini development board has a dedicated connector K11 to interface Servo motor. Regulated 5V is available on power supply pin and the signal pin is connected at the port pin PC6.
Note: Use adapter for powering since USB doesn’t provide required current.
Schematic
Sample Code
Sample code to check servo motor is given below. Upon code execution, the servo wipes continuously.
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/************************************************************************************ HEADER FILES *************************************************************************************/ #define F_CPU 8000000UL #include<avr/io.h> /* Header File Inclusion */ #include<avr/interrupt.h> /* Interrupt File Inclusion */ #include<util/delay.h> /* Delay File Inclusion */ /************************************************************************************ VARIABLE DECLARATIONS *************************************************************************************/ volatile unsigned char Timer_Count; unsigned char Servo_Angle = 10; unsigned char Servo_Value = 0; unsigned char k = 0; volatile unsigned char count = 0; /************************************************************************************ FUNCTION DECLARATIONS *************************************************************************************/ unsigned char Convert_Angle(unsigned char k); /************************************************************************************ MAIN FUNCTION *************************************************************************************/ int main() { DDRC = 0X40; /* PC6 pin set as output for servo */ TCCR0 = 0X02; /* Prescalar is 8 */ TCNT0 = 0XEB; /* Timer count for 20micro second */ TIMSK = 0X01; /* Timer0 interrupt enable */ SREG = 0X80; /* Global interrupt enable */ while(1) { for(k=0; k<=150; k++) /* Loop for angle increment */ { /* Convert angle to count */ Servo_Value = Convert_Angle(Servo_Angle++); _delay_ms(10); } for(k=0; k<=150; k++) /* Loop for angle decrement */ { /* Convert angle to count */ Servo_Value = Convert_Angle(Servo_Angle--); _delay_ms(10); } } } /************************************************************************************ INTERRUPT SERVICE ROUTINE *************************************************************************************/ ISR(_VECTOR(9)) { TIFR=0X01; /* TOV0 flag cleared by writing logic1*/ Timer_Count++; /* Variable for count overflow */ if( Timer_Count < 125 ) /* Count for 180 degree i.e. 2.5ms */ TCNT0=0XEB; /* Load timer value for 20us pulse */ if( Timer_Count == Servo_Value ) PORTC &=~(1<<6); /* Clearing servo pin */ if( Timer_Count >= 125 ) /* Angle greater than 180 */ { TCNT0=0X97; /* 3.5 ms delay */ TCCR0=0X04; /* Set pin connected to servo */ } if( Timer_Count == 130 ) /* 17.5ms(5*3.5) ie:2.5+17.5=20mS */ { PORTC = 0X40; /* Set pin connected to servo */ TCCR0 = 0X02; /* CS01=1, prescalar is 8 */ TCNT0 = 0XEB; /* Load 20us pulse */ Timer_Count = 0; /* Clear timer count */ } } /************************************************************************************ * Function : Convert_Angle * * * * Description : Function to calculate timer count for angle * * * * Parameters : k, contains the angle to be convert * *************************************************************************************/ unsigned char Convert_Angle(unsigned char k) { unsigned char timer_value; int temp; temp = k*5; timer_value = temp/9; /* Timer value=(100/180)+25i.e(5/9)+25 */ timer_value = timer_value+25; _delay_ms(3); return timer_value; /* Return timer value */ } /**************************** END OF PROGRAM ***************************************/ |
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