Help me select an option to generate 25 kHz PWM

Projects General Guidance
1

Hi guys,

I'm running Mega with Marlin firmware (as my 3d printer controller) which to my understanding has its PWM set to 1 kHz.
I want to control a 4-wire fan (Pfc0612de) with PWM from 30% to 100% and to reduce noise I've decided to use the manufacturer's recommended 25 kHz (I won't need to read the tacho). I think I won't need to worry about phase and only need to control the duty cycle and frequency(?)

After searching I came up with a couple of options but I don't know which is easier or more plausible so here I am :grinning:

  1. change Mega's timer :
    I don't know If there are any unused timers by Marlin or not, and if there are, is it possible without affecting its other functionalities?

  2. using a standalone driver with 25 kHz output like MAX31790 (which I can't source, any alternatives?) :
    I'll have to send Marlin's fan control commands through I2c

  3. using PLL frequency multiplier from 1 to 25 kHz :
    3.1. 4046 with divide by 25 (2 MOD-5 7490) (0.3$ + 2x0.5$= 1.3$)
    3.2. lm565 with divide by 25 (2 MOD-5 7490) (4$ + 2x0.5$= 5$) (don't know if it's any better or not)
    I don't know if PLL preserves the duty cycle or not

  4. using another MCU (Attiny85 or ATmega328) to read the 1 kHz PWM and generate 25 kHz accordingly (4$) :
    with the same price as 3.2, I'll have unused pins for 2 more fans?

any help/guidance would be appreciated

2

My thinking …. Your link is to a brushless motor , which must therefore have a built in speed controller . The PWM input , I think is just to speed control it and therefore
PWM frequency may not affect it at all . The data sheet allows for a very wide range of PWM.( 30-300kHz)
I assume you have connected the motor to a suitable steady 12v DC supply ( say 2A min) and an Arduino PWM pin ( “analog output” ) to the pwm wire , with a common ground between the Arduino and motor supply.

I’ve never changed PWM frequency and someone may be along to help , or google it

3

hey hammy
thanks for the quick response
yes, it has built-in speed control, and I can run it with 1 kHz as it supports 30-300k Hz.
my main concern is the noise it'll make so I wanted to use the recommended 25 kHz
and those options are the ones I came up with after googling it :grinning:

4

It's pretty easy to adjust PWM frequency, Just need to determine the type of PWM needed and work through the steps.
Here is an excellent guide: Secrets of Arduino PWM

5

You don't need change the timer, you only should change the prescaler.
For example, for Timer1 on Mega you should add to the setup() this line:

TCCR1B = (TCCR1B & 0b11111000) | 0b00000001;

After that you can use analogWrite() in it usual way, but the PWM on pins 11 & 12 will run in 31.4 KHz

6

won't it affect Marlin firmware's functionality?

won't it affect other parts of the code using timer1?

8

of course yes, if others parts of your code are sensible to timer frequency change. But you always can choose another timer.

9

that was part of the question :grinning:

I need to achieve this without making fundamental changes to the code and its functionality as a 3d printer controller, that's why most of the options I came up with, are hardware.
of course, I'd prefer option 1 if it's possible as it has no additional cost, but ...

10

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