fm101
Member level 5
I got the following code from the internet. It is used to output sine signal using PWM.
(1)What I don't understand is that why there are two outputs from pin 4 and 10? output from pin 10 seems only square wave and not pwm for sine wave
(2) What is frequency of sine wave from pin 4 output?
(3) is it possible to output pwm sine signal on pin 10 for higher frequency 31250 Hz using the same code for pin 4?
thanks
(1)What I don't understand is that why there are two outputs from pin 4 and 10? output from pin 10 seems only square wave and not pwm for sine wave
(2) What is frequency of sine wave from pin 4 output?
(3) is it possible to output pwm sine signal on pin 10 for higher frequency 31250 Hz using the same code for pin 4?
thanks
C-like:
uint8_t pVal = 127; //PWM value
const float pi2 = 6.28; //Pie times 2, for building sinewave
const int samples = 100; //number of samples for Sinewave. This value also affects frequency
int WavSamples[samples]; //Array for storing sine wave points
int count = 0; //tracks where we are in sine wave array
void setup() {
// Serial.begin(115200); //for debugging
pinMode(10, OUTPUT); //pin used for analog voltage value
pinMode(4,OUTPUT); //pin used to fake PWM for sinewave
setPwmFrequency(10,1); //function for setting PWM frequency
analogWrite(10,127); //set duty cycle for PWM
float in, out; //used for building sine wave
for (int i=0;i<samples;i++) //loop to build sinewave
{
in = pi2*(1/(float)samples)*(float)i; //calculate value for sine function
WavSamples[i] = (int)(sin(in)*127.5 + 127.5); //get sinewave value and store in array
// Serial.println(WavSamples[i]); //for debugging
}
}
void loop() {
if(count > samples) count = 0; //reset the count once we are through array
bitBangPWM(WavSamples[count],4); //function for turning sinewave into "fake" PWM signal
count++; //increment position in array
}
//Function to bit bang a PWM signal (we are using it for the sinewave)
//input are PWM high value for one cycle and digital pin for Arduino
//period variable determines frequency along with number of signal samples
//For this example a period of 1000 (which is 1 millisecond) times 100 samples is 100 milli second period so 10Hz
void bitBangPWM(unsigned long on, int pin) {
int period = 1000; //period in micro seconds
on = map(on, 0, 255, 0, period); //map function that converts from 8 bits to range of period in micro sec
// Serial.println(on); //debug check
unsigned long start = micros(); //get current value of micro second timer as start time
digitalWrite(pin,HIGH); //set digital pin to high
while((start+on) > micros()); //wait for a time based on PWM duty cycle
start = micros();
digitalWrite(pin,LOW); //set digital pin to low
while((start+(period - on)) > micros()); //wait for a time based on PWM duty cycle
}
/**
* https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM
* Divides a given PWM pin frequency by a divisor.
*
* The resulting frequency is equal to the base frequency divided by
* the given divisor:
* - Base frequencies:
* o The base frequency for pins 3, 9, 10, and 11 is 31250 Hz.
* o The base frequency for pins 5 and 6 is 62500 Hz.
* - Divisors:
* o The divisors available on pins 5, 6, 9 and 10 are: 1, 8, 64,
* 256, and 1024.
* o 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
*
* Note that this function will have side effects on anything else
* that uses timers:
* - 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.
* - Changes on pins 9 or 10 will cause the Servo library to function
* incorrectly.
*
* Thanks to macegr of the Arduino forums for his documentation of the
* PWM frequency divisors. His post can be viewed at:
* http://forum.arduino.cc/index.php?topic=16612#msg121031
*/
void setPwmFrequency(int pin, int divisor) {
byte mode;
if(pin == 5 || pin == 6 || pin == 9 || pin == 10) {
switch(divisor) {
case 1: mode = 0x01; break;
case 8: mode = 0x02; break;
case 64: mode = 0x03; break;
case 256: mode = 0x04; break;
case 1024: mode = 0x05; break;
default: return;
}
if(pin == 5 || pin == 6) {
TCCR0B = TCCR0B & 0b11111000 | mode;
} else {
TCCR1B = TCCR1B & 0b11111000 | mode;
}
} else if(pin == 3 || pin == 11) {
switch(divisor) {
case 1: mode = 0x01; break;
case 8: mode = 0x02; break;
case 32: mode = 0x03; break;
case 64: mode = 0x04; break;
case 128: mode = 0x05; break;
case 256: mode = 0x06; break;
case 1024: mode = 0x07; break;
default: return;
}
TCCR2B = TCCR2B & 0b11111000 | mode;
}
}
