Higher resolution PWM

Other Hardware General Electronics
1

Hi, any suggestion for an higher resolution (12bit or 16 bit) PWM solution for Arduino?
I've heard of shields from Sparkfun, Adafruit etc but I don't know if they fit my needs.

I need to send PWM signals to a Meanwell LDD led driver, and using the 8 bit native Pwm of the Arduino results in horrible and visible steps instead of a smooth LED dimming.

Thanks :slight_smile:

2

Timer 1 is 16bit. You can get better PWM out of that one.

3

Sorry, I forgot to mention I have to pwm 6 LDD drivers, so pins 9 & 10 are not enough.

4

Then you'll need extra hardware to get more than 8bit resolution on that many pins.

5

If you need more than 255 levels then you'll need to write a software PWM. The simplest way to do that would be to grab the softPWM library and change the "value" size from an 8 bit int to a 16 bit int.

6

@Delta_G: yes, any IC/shield you have experience of?

@Chagrin: thanks, this could be an option but as I control a temperature sensor, an LCD, read values from 6 pots I fear I would have incorrect timings

7

You may want to check out Bit Angle Modulation. It's way more gentle to the microprocessor than PWM and the values/brightness scale better.

8

@Vinter: thanks, very interesting! But unfortunately my power led drivers (in fact, most power led drivers) only understand PWM :~

9

You can also get more resolution with DDA techniques, averaged over many cycles.

10

Hi, can you please explain me what are DDA techinques?

11

Try Adafruit 16-Channel 12-bit PWM/Servo Driver - I2C interface [PCA9685] : ID 815 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits for 12 bit (4096 steps) PWM resolution.

I believe MarkT is referring to "digital differential analyzer". See http://simplicate.weebly.com/1/post/2013/05/using-bresenham-line-algorithm-for-better-pwm.html for a good explanation of the concept; the general idea is that you get less flicker if you spread the on/off pulses over the entire cycle rather a single on/off pulse per cycle that PWM defines.

12

If you're prepared to devote some CPU time to the job you can do very high resolution PWM in software (on many pins...)

13

@Fungus: can you show me how?

14 
// 16-bit PWM
unsigned int brightness = XXXX;

unsigned int counter=0;
while (true) {
  if (counter==0) {
    changeBrightness();
    if (brightness!=0) {
      turnLEDon();
    }
  }
  ++counter;
  if (counter == brightness) {
    turnLEDoff();
  }
}
15

Thank you