This is out of my league, but I really need to increase the PWM to 20khz on digital pin 9. I'm powering a motor that is used in conjunction with audio equipment so I need the PWM to be out of hearing range.
The motor driver datasheet says it supports up to 20 KHz PWM. It's the VNH2SP30. Data sheet here:
I've read a few different pages here at Arduino.cc on PWM regarding changing the default (500) to something higher. If I understand it right, it's somewhat easy to change it to some standard frequencies but to get 20Khz, I don't know. My atmega328 chip really won't be doing a whole lot, so it won't matter if it messes up my millis() function. I understand that is somewhat compromised by changing the PWM setting?
Thanks for the support.
Pin D9 is the output from the Timer/Counter 1 Output Compare Register A (ORC1A). The highest speed you can run it at is 16 million steps per second or 62.5 kHz for 9-bit PWM (16 MHz / 256 steps). The way to get 20 kHz is to have the timer reset at 800 (16,000,000 / 20,000) instead of 256. This give you a PWM range from 0 to 799.
That's in the Fast PWM mode. For PWM modes where the timer counts up and then down (Phase Correct or Phase and Frequency Correct PWM) you would count up to 400 and back down to 0.
Read all Timer/Counter 1 and PWM modes in the ATmega328p datasheet.
I've spent an hour reading through pages like "secretOfArduinoPWM", "PwmFrequency", "TimerPWNCheatsheet", About all I could get was that something called TCCR1B affects the timer1 which operates pin 9. This is WAY over my head. I've seen different examples, but I don't even know which of them to start with.
The data sheet for the VNH2SP30 says, "PWM OPERATION UP TO 20 KHz". So I assume if it were higher it might jitter or something, which would definitely not be acceptable
No, just pin 9. The VHN2SP30 only uses 1 pin for PWM, then 2 other pins for enabling each side. I already sent off for my pcboard, or I'd say any PWM pin would work. I guess I could make a new board if 20Khz PWM isn't possible on pin 9.
SouthernAtHeart:
I've spent an hour reading through pages like "secretOfArduinoPWM", "PwmFrequency", "TimerPWNCheatsheet", About all I could get was that something called TCCR1B affects the timer1 which operates pin 9. This is WAY over my head. I've seen different examples, but I don't even know which of them to start with.
That's a good start. Each of the three timers has two PWM outputs (A and B). For Pin 9 you have to look at which timer controls it:
That spreadsheet shows that on an UNO the Pin 9 PWM comes from Timer 1 output A (T1A) and on the ATmega it's known as Port B Pin 1 (PB 1). If you switch to a Mega you need to change to Timer 2 output B (T2B) which on the ATmega is known as Port H Pin 6 (PH 6).
Knowing you want Timer/Counter 1 you read that section of the datasheet. It talks about the Timer Counter Registers: TCCR1A, TCCR1B, and TCCR1C (they had too many bit to fit in one byte so they made it into three registers).
TIMSK1: The Interrupt Mask Register. Since you aren't using interrupts this remains 0.
TIFR1: Interrupt Flag Register. Since you aren't using interrupts this isn't important.
Since it is a 16-bit counter the other registers are two bytes each:
TCNT1: The actual timer/counter count
OCR1A: The 'A' Output Compare Register that is associated with Pin 9
OCR1B: The 'B' Output Compare Register associated with a different pin.
ICR1: The Input Capture Register. In out case we are using it to set the TOP of the counting range so the counter doesn't go all the way to 65535.
thanks. Yes, I got the VNH2SP30 for that very reason, that it goes up to 20Khz.
I don't have a scope, but I do have a Fluke meter that measures frequency. I've never used that function, but I'll have to test it out, it'll be good learning.
Hi guys!
Your answers are great and very useful as I have the very same VNH2SP30 chip on my motomonster Hbridge (sparkfun https://www.sparkfun.com/products/10182)
but I would like to drive two motors! I have read in the code that "Channel B is irrelevant" and I'm lost...
Could you please tell me what to implement in order to have D9 and D10 ultrasonic's POWER
Thanks Coding Badly for your quick reply! and commented code 8)
Wonderful!
It seems that because the 2 pins are sharing the same timer (PWM T1), it's quite short to implement: excellent! I woudn't have dared to mess with the code: registry frighten me!
I'll have a try now with my Nano ATMega 328
To be compliant with the rest of my code, can I use this (map and constrain) without decreasing the overall performance?
void analogWriteSAHA( uint8_t value )
{
// My variable value varies from 0 to 255
// but awaited range in OCR1A is from 0 to 799 and nothing else!
OCR1A = constrain(map(value, 0, 255, 0, 799), 0, 799);
}
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