DIY Arduino‎ > ‎

Variable frequency PWM


It's handy to have a variable frequency PWM,

How to adjust Arduino PWM frequencies

by macegr in this forum post http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235060559/12

Pins 5 and 6: controlled by Timer 0

Setting 	Divisor 	Frequency
0x01 	 	1 	 	62500
0x02  		8 	 	7812.5
0x03  		64 	 	976.5625
0x04 	 	256 	 	244.140625
0x05 	 	1024 	 	61.03515625

TCCR0B = TCCR0B & 0b11111000 | <setting>;
http://playground.arduino.cc/Main/TimerPWMCheatsheet

http://arduino-info.wikispaces.com/Arduino-PWM-Frequency

ICR1 = 10,000 gives f = 100Hz
ICR1 = 5000 gives f = 200Hz
ICR1 = 2500 gives f = 500Hz
ICR1 = 1000 gives f = 1kHz
ICR1 = 500 gives f = 2kHz
ICR1 = 333 gives f = 3kHz
ICR1 = 250 gives f = 4kHz
ICR1 = 100 gives f = 10kHz

http://www.oxgadgets.com/2011/04/creating-a-variable-frequency-pwm-output-on-arduino-uno.html

Turns out that this script does the trick.

unsigned long duty1,duty2;
// Duty Cycle in terms of a percentage.
unsigned long plus;
// Value read from A1, in case plus mode is activated
float xxx;
// Float numbers to calculate duty for PWM 1 and PWM 2
float yyy;
unsigned long pwm1;
// Value read from A0 and A2 to give PWM duty cycle output in terms // of 0-5V
unsigned long pwm2;
void setup(){
pinMode(9, OUTPUT);
pinMode(10, OUTPUT);
TCCR1A = _BV(COM1A1) | _BV(COM1B1) ; // phase and frequency correct mode. NON-inverted mode
// TCCR1A = _BV(COM1A1) | _BV(COM1B1) | _BV(COM1A0) | _BV(COM1B0) ;
//phase/frequency correct mode. SELECT THIS FOR INVERTED OUTPUTS.
TCCR1B = _BV(WGM13) | _BV(CS11);
// Select mode 8 and select divide by 8 on main clock.
}
void loop(){
// Program that lets different values on A3 choose different values of frequency, e.g. 100,200,400,500,1k,2k,3k,4k,10k,
//etc in relation with a free input.
if (analogRead(A3) <100) ICR1 = 10000; // 100Hz - Default value to 100Hz for A3 = 0V
if (analogRead(A3) <200 && analogRead(A3) > 100) ICR1 = 5000; // 200Hz
if (analogRead(A3) <300 && analogRead(A3) > 200) ICR1 = 2500; // 400Hz
if (analogRead(A3) <400 && analogRead(A3) > 300) ICR1 = 1000; // 1000Hz
if (analogRead(A3) <500 && analogRead(A3) > 400) ICR1 = 500; // 2000Hz
if (analogRead(A3) <600 && analogRead(A3) > 500) ICR1 = 333; // 3000Hz
if (analogRead(A3) <700 && analogRead(A3) > 600) ICR1 = 250; // 4000Hz
if (analogRead(A3) <800 && analogRead(A3) > 700) ICR1 = 100; // 10000Hz
if (analogRead(A3) > 800) ICR1 = 1000; // Default value to 1kHz for A3 = 5V
//ICR1 = 1000; // for ICR1 = 1000, frequency = 1kHz.
pwm1 = analogRead(A2); // read duty from A2 for PWM 2
pwm2 = analogRead(A0); // read duty from A0 for PWM 1
xxx = float(pwm2);
// Turn read values from the POTs to float for mathematical
// adjustment.
yyy = float(pwm1);
xxx = xxx * ICR1;
// Multiply with ICR1 and divide by 1023 to give required percentage
yyy = yyy * ICR1;
xxx = xxx / 1023;
yyy = yyy / 1023;
//Assign values to OCR Registers, which output the PWM duty cycle.
OCR1B = int(xxx);
OCR1A = int(yyy);
}