How to precisely control servo motor by changing duty cycle?

Question

I developed a PWM using timer1,using arduino uno and digital output, and identified that when I send a wave with duration of 0.6ms in High level, the motor goes to 0o. If I send 2.1ms, it goes to 180o. I tried to make a relationship between these scales to send the angle and change the time period in order to achieve that angle and it did not work.

I would like to move with a precision of 1 degree, is that possible? Just adjusting the time period.

The model of the motor is mg996r. Maybe I am missing something.

My code just generates an interrupt over 50 microsencods and I use this to set the frequency of 50Hz and the duty cycle in ms using digitalWrite associated with pin 9.

#include <TimerOne.h>
double t = 0.0;
double period = 0;
void setup() 
{
 t = 0;
 Serial.begin(9600);
 pinMode(9, OUTPUT); 
 Timer1.initialize(50);
 Timer1.attachInterrupt( timerIsr ); // attach the service routine here
}
void loop()
{
 // Main code loop
 // TODO: Put your regular (non-ISR) logic here
 if (Serial.available() > 0) {
 float grau = Serial.parseFloat();
 // receive data as angle
 if (grau > 180) grau = 180;
 if (grau < 0) grau = 0;
 // set period for that angle
 // relationship developed between angle and period in ms
 //set it to period
 period = (0.00833*grau + 0.6)*1E-3; 
 }
}
/// --------------------------
/// Custom ISR Timer Routine
/// --------------------------
void timerIsr()
{
 t += 50E-6;
 if (t <= period) {
 digitalWrite(9, HIGH);
 }
 else if (t < 20E-3) { // periodo max de 20ms -> 50Hz
 digitalWrite(9, LOW);
 }
 else {
 t = 0;
 }
}

UPDATE:

I just got it working by creating a timer1 interrupt on CTC mode with a frequency of 100kHz and counting the necessary time to get increments (~ 10us each) of around 1 degree on my servo motor.

More info here.

• bpinhosilva: The relationship is like a map between 0.6 ms -> 2.1ms and 0 -> 180 angle degrees. It works, but the problem is that it does not work for a precision of 1 angle degree as Arduino Servo Library does...
• Roger Rowland: For a precision of one degree, you need a minimum timer increment of 8.33us, which is optimistic. Your current 50us period gives you a resolution of ~6 degrees.
• bpinhosilva: I tried a resolution of 1us but it didn't work, the motor did not move. Can I achieve this using timer1?
• bpinhosilva: I found that it has a dead band of 5us. So it won't move until the width changes by 5us.

Answer 1

The best is to use 10us Period, instead of 50us.
That precision will be close to 1°

• bpinhosilva: Thanks, @Mathsman, I got it working, you were right! Just created a timer1 interrupt using CTC mode and then generated an output signal with a frequency of 100kHz that I could increment the angle by approximately 1 degree.
• Mathsman 100: Your welcome. I recommended this as I have already tried it.
• Mathsman 100: It has precision of 1.1to 1.2 degrees.