Changing Frequency of PWM Pin on Arduino Uno

Question

I am trying to change the frequency of the PWM output from an Arduino Uno R3 (Been using Pin 9) to 200 Hz with a duty cycle of 20%. This is for an ESC that is connected to a 12V motor, and I know the ESC works as if I input a 200 HZ wave from a waveform generator the motor runs. However, I have been finding it difficult to do the same thing with an Arduino Uno and I believe it is due to the frequency being a default of 490 Hz, so I need a way to change that frequency to 200 Hz. Are there any libraries or specific ways to do so?

Thanks!

• jsotola: please add your code to the post ... format as "code"
• chrisl: Haven't used a library for this yet, but you can find promising results in a web search. Like this library

Answer 1

You can also use my newly-created AVR_PWM library to shield you from dealing with complex hardware registers

For example

#include "AVR_PWM.h"
#if ( PWM_USING_ATMEGA2560 )
 // Pins tested OK in Mega
 //#define pinToUse 12 // Timer1B on Mega
 //#define pinToUse 11 // Timer1A on Mega
 //#define pinToUse 9 // Timer2B on Mega
 //#define pinToUse 2 // Timer3B on Mega
 //#define pinToUse 3 // Timer3C on Mega
 //#define pinToUse 5 // Timer3A on Mega
 //#define pinToUse 6 // Timer4A on Mega
 //#define pinToUse 7 // Timer4B on Mega
 #define pinToUse 8 // Timer4C on Mega
 //#define pinToUse 46 // Timer5A on Mega
 //#define pinToUse 45 // Timer5B on Mega
 //#define pinToUse 44 // Timer5C on Mega
#elif ( PWM_USING_ATMEGA_32U4 )
 // Pins tested OK on 32u4
 //#define pinToUse 5 // Timer3A on 32u4
 #define pinToUse 9 // Timer1A on 32u4
 //#define pinToUse 10 // Timer1B on 32u4
#else
 // Pins tested OK on Nano / UNO
 #define pinToUse 9 // Timer1A on UNO, Nano, etc
 //#define pinToUse 10 // Timer1B on UNO, Nano, etc
 //#define pinToUse 5 // Timer0B on UNO, Nano, e
 //#define pinToUse 3 // Timer2B on UNO, Nano, etc
#endif
//creates pwm instance
AVR_PWM* PWM_Instance;
float frequency;
float dutyCycle;
void setup()
{
 Serial.print(F("\nStarting PWM_Basic on "));
 Serial.println(BOARD_NAME);
 Serial.println(AVR_PWM_VERSION);
 //assigns PWM frequency of 200 Hz and a duty cycle of 0%
 PWM_Instance = new AVR_PWM(pinToUse, 200, 0);
}
void loop()
{
 frequency = 200;
 dutyCycle = 20;
 PWM_Instance->setPWM(pinToUse, frequency, dutyCycle);
 delay(10000);
 dutyCycle = 90;
 PWM_Instance->setPWM(pinToUse, frequency, dutyCycle);
 delay(10000);
}

Answer 2

If you are prepared to use Timer 2 (Pin D3) this code will do it:

void setup() 
 {
 pinMode (3, OUTPUT);
 TCCR2A = bit (WGM20) | bit (WGM21) | bit (COM2B1); // fast PWM, clear OC2B on compare
 TCCR2B = bit (WGM22) | bit (CS20) | bit (CS21) | bit (CS22); // prescaler of 1024
 OCR2A = 77; // zero relative 
 OCR2B = 15; // 20% duty cycle
 } // end of setup
void loop()
 {
 // do other stuff here
 }

More information on the Atmega328P timers on my page about timers.

The figure 77 is obtained from:

16000000 / 1024 / 78 = 200.32

In other words, the prescaler of 1024 is divided into the clock of 16 MHz, and then we count up to 78, giving a result of just over 200. I actually use 77 because the timer is zero-relative (it counts from 0 to 77, giving 78 counts). This means the frequency is slightly out (it will be 200.32 Hz rather than 200 but that could be close enough).

---

You could also do it with Timer 1 (pin D10) to get slightly more accurate results, like this:

void setup() 
 {
 pinMode (10, OUTPUT);
 // mode 15
 TCCR1A = bit (WGM10) | bit (WGM11) | bit (COM1B1); // fast PWM, clear OC1B on compare
 TCCR1B = bit (WGM12) | bit (WGM13) | bit (CS11); // fast PWM, prescaler of 8
 OCR1A = 10000 - 1; // what to count to
 OCR1B = 2000 - 1; // duty cycle
 } // end of setup
void loop()
 {
 // do other stuff here
 }

In this case I have used a prescaler of 8 and a count-up value of 10000, as follows:

16000000 / 8 / 10000 = 200

In this case the answer is exactly 200, which will be more accurate than the 200.32 obtained from using Timer 2. That is because Timer 1 is a 16-bit timer and has higher resolution.