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Set PWM frequency to 25 kHz

I currently can set four PWM pins to around 31 kHz with the following code:

void setup()
{
 TCCR1B = TCCR1B & B11111000 | B00000001; // Set PWM frequency for D9 & D10:
 pinMode(pwmPin9, OUTPUT); // Sets the pin as output
 pinMode(pwmPin10, OUTPUT); // Sets the pin as output
 TCCR2B = TCCR2B & B11111000 | B00000001; // Set PWM for D3 & D11
 pinMode(pwmPin3, OUTPUT); // Sets the pin as output
 pinMode(pwmPin11, OUTPUT); // Sets the pin as output
}

I found this setup somewhere, but I don't know how I can set these four PWM pins to around 25 kHz instead. How is that possible?

Answer*

You can configure Timer 1 to cycle at 25 kHz in phase correct PWM mode, and use it's two outputs on pins 9 and 10 like so:



 // PWM output @ 25 kHz, only on pins 9 and 10.
 // Output value should be between 0 and 320, inclusive.
 void analogWrite25k(int pin, int value)
 {
 switch (pin) {
 case 9:
 OCR1A = value;
 break;
 case 10:
 OCR1B = value;
 break;
 default:
 // no other pin will work
 break;
 }
 }

 void setup()
 {
 // Configure Timer 1 for PWM @ 25 kHz.
 TCCR1A = 0; // undo the configuration done by...
 TCCR1B = 0; // ...the Arduino core library
 TCNT1 = 0; // reset timer
 TCCR1A = _BV(COM1A1) // non-inverted PWM on ch. A
 | _BV(COM1B1) // same on ch; B
 | _BV(WGM11); // mode 10: ph. correct PWM, TOP = ICR1
 TCCR1B = _BV(WGM13) // ditto
 | _BV(CS10); // prescaler = 1
 ICR1 = 320; // TOP = 320

 // Set the PWM pins as output.
 pinMode( 9, OUTPUT);
 pinMode(10, OUTPUT);
 }

 void loop()
 {
 // Just an example:
 analogWrite25k( 9, 110);
 analogWrite25k(10, 210);
 for (;;) ; // infinite loop
 }

Writing a value of 0 with `analogWrite25k()` means the pin will be
always LOW, whereas 320 means always HIGH. The regular `analogWrite()`
should _almost_ work, but it will interpret 255 the same as 320 (i.e.
always HIGH).

This code assumes an Arduino Uno or similar board (ATmega168 or 328 @
16&nbsp;MHz). The method used here requires a 16-bit timer, and thus it
uses Timer 1 as it's the only one available on the Uno; that's why only
two outputs are available. The method could be adapted to other
AVR-based boards with a 16-bit timer. As Gerben noted, that timer should
have a corresponding ICRx register. There are 4 such timers on the
Arduino Mega, each with 3 outputs.

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1

It might be useful to explain that this method only works for timer1, as the other timers don't have a ICRx register. At most, you can only have one PWM pin per timer, for timers 0 and 2.

Gerben
– Gerben

2016年06月24日 13:04:19 +00:00
Commented Jun 24, 2016 at 13:04
1

@Gerben: Don't all the 16-bit timers have that register? At least on the Mega they do.

Edgar Bonet
– Edgar Bonet

2016年06月24日 13:09:20 +00:00
Commented Jun 24, 2016 at 13:09
1

Yes, but only timer1 is 16-bit on the ATMega328. The rest are 8-bit. And the OP wants 4 PWM output, and your solution only provides 2. Or am I mistaken?

Gerben
– Gerben

2016年06月24日 15:12:53 +00:00
Commented Jun 24, 2016 at 15:12
1

@Gerben: No, you are right. I just say that requiring ICRx seems to be redundant with requiring the timer to be 16-bits. For the Uno and Mega at least, not sure about other AVR-based Arduinos. The OP understand this only provides 2 PWM channels: see my comment on his question and his answer.

Edgar Bonet
– Edgar Bonet

2016年06月24日 15:48:45 +00:00
Commented Jun 24, 2016 at 15:48
2

@techniche: 1. Works for me. Maybe you forgot to set COM4C1 in TCCR4A? 2. If that's not the problem, then read How do I ask a good question?, then update your question by including your full source code and clearly stating what you expect the program to do and what it does instead ("I dont see any success" is not considered a valid problem statement).

Edgar Bonet
– Edgar Bonet

2017年09月15日 08:43:10 +00:00
Commented Sep 15, 2017 at 8:43

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