Arduino Nano PWM frequency

Question 1

I have been using an Arduino Nano as a PWM controller for a heating element.

I am currently usingD11 (PB3). I could change, although all pins with PWM are in use, and would require a re-write and re-wire.

This produces a signal at ~490Hz, but I would like to experiment with changing this to a higher frequesncy.

I gather it its possible to vary the frequency by changing the divisor from its default 64.

My sketch uses Useshttp://playground.arduino.cc/Main/SevenSegmentLibrary and calls millis() - will changing PWM divisor impact on either of these?

NOTE I have read thesetPwmFrequency documentation, but find "disrupts the normal operation" unhelpful - I am actually after some explanation of the concrete effect. I only usemillis() to time button presses and flash a LED, which are not time critical

Please keep in mind that changing the PWM frequency changes the Atmega's timers and disrupts the normal operation of many functions that rely on time (delay(), millis(), Servo library).

I have been doing some further study.http://playground.arduino.cc/Code/PwmFrequency statesChanges on pins 3, 5, 6, or 11 may cause the delay() and millis() functions to stop working.

Other references say 3, 11 usetimer 2 sodo they affectmillis() or not as other references claimtimer 0 is used for these.

Question 2

Yes and no, depending on the pwm timer used.

Question 3

I don't know where this misinformation comes from... The answer isno, reconfiguring Timer 2 doesnot affectmillis() nordelay(), as these functions rely on Timer 0. AFAIK the Arduino coredoes not use Timer 2 at all. But note that there may be other Arduino orthird party libraries that rely on Timer 2.

You can see here thesource code ofmillis() anddelay().

As MITU RAJ correctly states in his answer, the PWM signal on pin 11 isprovided by Timer 2, so you can use it safely.

Question 4

The misinformation comes fromplayground.arduino.cc/Code/PwmFrequency. I am sure I am not the only user to have been mislead. The other answer just published an extract of the misleading documentation.

Question 5

Depends on the pin you used for the PWM.

Arduino UNO/NANO specs say following things:

The base frequency for pins 3, 9, 10, and 11 is 31250 Hz.

The base frequency for pins 5 and 6 is 62500 Hz.

The divisors available on pins 5, 6, 9 and 10 are: 1, 8, 64, 256, and 1024.

The divisors available on pins 3 and 11 are: 1, 8, 32, 64, 128, 256, and 1024.

PWM frequencies are tied together in pairs of pins. If one in a pair is changed, the other is also changed to match.

Pins 5 and 6 are paired on timer0.

Pins 9 and 10 are paired on timer1.

Pins 3 and 11 are paired on timer2.

Changes on pins 3, 5, 6, or 11 may cause the delay() and millis() functions to stop working. Other timing-related functions may also be affected.

Question 6

Since you're quoting the specs, it'd be nice if you could also link to them? :)

Question 7

The answer isNO, changing the PWM divider for pin 11 will not affect themillis() function (nordelay()).

Explanation:
TheArduino Nano uses the ATMega328P microcontroller, same as theArduino Uno.

Pin 11's PWM is controlled by Timer 2. By default Timer 2 has a prescale of 64 (ie. setting 0x04). The base frequency of Timer 2 is 31372.55 Hz resulting in a frequency of 490.2 Hz (ie. 31372.55/64 = 490.1961).

On the other hand, the microsecond timer (ie. the one used bymillis(),micros(),delay() anddelayMicroseconds()) is controlled by Timer 0.

So changing the prescaler of Timer 2 will not affectmillis().

It will however change the PWM frequency of Pin 3.

Back to your question:
The possible PWM frequencies of Pin 11 (higher than 488 Hz) are:

31373 / 32 = 980.4 Hz
31373 / 8 = 3921.6 Hz
31373 / 1 = 31373 Hz

Where 32, 8, 1 are the prescaler.
Which equates to a setting value of 0x03, 0x02 & 0x01 respectively.

Add this line of code:

TCCR2B = TCCR2B & 0b11111000 | setting;

Wheresetting is the value of the setting for the respective prescaler.

============================================  || Frequency [Hz] || Prescaler || Setting ||  ============================================  || 31373.55       || 1         || 0x01    ||  || 3921.57        || 8         || 0x02    ||  || 980.39         || 32        || 0x03    ||  || 490.20         || 64        || 0x04    ||  || 245.10         || 128       || 0x05    ||  || 122.55         || 256       || 0x06    ||  || 30.64          || 1024      || 0x07    ||  ============================================

Source code:https://github.com/arduino/ArduinoCore-avr/blob/master/cores/arduino/wiring.c

Question 8

Just nitpicking but... the timer's base frequency in phase correct PWM mode is F_CPU/510 (31373 Hz), not F_CPU/512: it takes 255 cycles to count from 0 to 255, then 255 more to count back to zero. C.f. the equation for the PWM frequency in the datasheet.

Question 9

@EdgarBonet Good point. The answer has now been corrected.

Question 10

would it be possible to go down a step slower to 15.31 HZ?

Edgar Bonet 45.2k4 gold badges42 silver badges81 bronze badges · Accepted Answer · 2021-10-08 05:12:03Z

I don't know where this misinformation comes from... The answer isno, reconfiguring Timer 2 doesnot affectmillis() nordelay(), as these functions rely on Timer 0. AFAIK the Arduino coredoes not use Timer 2 at all. But note that there may be other Arduino orthird party libraries that rely on Timer 2.

You can see here thesource code ofmillis() anddelay().

As MITU RAJ correctly states in his answer, the PWM signal on pin 11 isprovided by Timer 2, so you can use it safely.

The misinformation comes fromplayground.arduino.cc/Code/PwmFrequency. I am sure I am not the only user to have been mislead. The other answer just published an extract of the misleading documentation.

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Arduino Nano PWM frequency

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