How can I make an AC analog voltage with Arduino?

Question

I am trying to create an AC voltage in Arduino. Until now I have only managed to get a square wave. How can this be achieved with Arduino?

If I try:

int up;
int down;
int out = 11;
void setup() {
 pinMode(out, OUTPUT);
 Serial.begin(9600);
}
void loop() {
 for (up = 0; up <= 255; up++) {
 analogWrite(out, up);
 delay(1);
 }
 for (down = 255; down >= 0; down--) {
 analogWrite(out, down);
 delay(1);
 }
}

is it still pulsed DC?

• user31481: Yes, it is still a square wave, varying between 0V and 5V. You need some extra hardware to do that.
• Majenko: What kind of frequency are you looking for? Do you want a sinewave, triangle wave, saw-tooth wave ... ?
• dandavis: just use an opamp to turn your square wave into a sine wave with a few caps and resistors

Answer 1

You have a few options:

• Use a low-pass filter to round the square wave's edges some so they look more AC-ish.

• Use a low-pass filter and have your code create steps of voltage that look AC-ish by varying the PWM widths.

• Use an external SPI DAC chip that you can control with more discrete levels to make smoother looking AC.

• Look into Direct Digital Synthesis (DDC) to learn more. Google "analog via ddS", lots of hits.