ATTiny85 based class D amplifier.

[Caleb6543]

This is my first foray into class D amplifiers. It is an implementation of Dimitrov's ATTiny based design which can be found here. I modified the code a bit to remove a DC offset and programmed it with the Arduino IDE.

My circuit has a high pitched noise problem, but otherwise seemed to do a decent job. I just thought someone might be interested. Although, I am certain you are all familiar with it already.

My goal was a small amplifier for my bass guitar. This does not have enough gain to take the raw signal and send it to the speaker. I'm working on a different circuit that uses a TPA3125 and includes a pre-amp.

/*
Class D Amplifier ATTiny85 Controller Sketch
last updated 6-23-2014
*/

#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <stdint.h>

#define DACP OCR1A
#define DACN OCR1B

// variable declarations

byte time;

unsigned int pos;
unsigned int neg;
unsigned int adc;

int val1 = 0;
int errorSum = 0;

void setup() {    
    
// Disable global interrupts
    cli();

// Configure ports
    DDRB = B00010010;
    PORTB = B11100100;

// Configure ADC
    ADMUX = B11010011;
    ADCSRA = B11000100;
    
// Power reduction
    PRR = B00000110;
    MCUCR = B00100000;
    
// Configure PWM
    TCCR1 = B01100010;
    GTCCR = B01100000;
    TIMSK = B100;
    PLLCSR = B110;
    
// Enable global interrupts
    sei();        
}

void loop() {
    sleep_cpu();
}
   

ISR(TIMER1_OVF_vect) {
    if(1 & ++time){
      adc = ADC;
      val1 = (adc >> 2) - 127 - (errorSum >> 10);
      errorSum = errorSum + val1;
      
      pos = 127 + val1;
      neg = 128 - val1;

      DACP = (pos & 255);
      DACN = (neg & 255);
    } else {
      DACP = (pos & 255);
      DACN = (neg & 255);    
    }
}

 

[theAnonymous1]

Maybe a good learning exercise, but kind of pointless considering it doesn't have any feedback.

Lot's of options out there for proper compact class-d amplifiers.

 

[dbutler6259]

Since its been about a year, has any one had any success with this circuit?

 

[Anung]

any schematic for this design?

 

[Aucosticraft]

well this could be a good experiment but AVR is too slow for any of the activities..

sure it would be fun.

 

[doctormord]

Why to slow? It ain't doing much.

 

[gmarsh]

The ATTiny85 has plenty of processing grunt. I'm using an ATTiny25 (85 w/less flash) in this guy:

https://www.youtube.com/watch?v=SlrnY7rLIJ4

I'm reading 31.25KHz, 8-bit data from a SPI flash chip using the USI peripheral, doing a 4x linear interpolation up to 125KHz, and feeding the output timer with the upsampled signal. Including wake from sleep and interrupt overhead, I'm using ~50% of the available 8MHz cycles.

Main limitations of this chip as a class D amplifier are going to be the limited dynamic range and accuracy of the 10 bit ADC.

 

[kenpeter]

I don't know what I/O features are offered in ATTtiny.
But wouldn't an analog feedback loop built around a
comparator (if by chance pins can be configured that
way) be of higher fidelity than any number ADC bits
input with an open loop PWM output?

 

[doctormord]

Why should it. Feedback is mostly used to limit bandwidth and correct "things".

 

[Caleb6543]

I wasn't too happy with my results and ended up using a dedicated chip. It could be my poor implementation and not the processor.

I was trying to duplicate this guy's results: https://youtu.be/CrAB9rIcakE

 

[amiak]

Caleb6543, thanks for posting! At some point I wondered, if the chip can be programmed successfully for this project with Arduino as ISP at all. Your code showed me, where I was wrong.

My circuit has a high pitched noise problem, but otherwise seemed to do a decent job.

Did you try to use Dimitrov's code without changes? I find this line particularly interesting:

      val1 = (adc >> 2) - 127 - (errorSum >> 10);

It gave me a clicking sound once every second or so. Removing (errorSum >> 10) helped. But I ended up using original Rouslan Dimitrov's code anyway (with slightest changes).

Also, burning correct fuses on ATtiny might help in your case.

My version of the amp is here. I was also planning to make a small amplifier for my acoustic-electric guitar.

I have one unexpected effect with the amp, however:
when the input gets too loud, the speakers get absolutely quiet (stuck in a certain position) and the sound doesn't return even after making input quiet again. I have to turn the amp off and on again to return the music in cases like that. I don't understand what's going on.

 

[doctormord]

Seems like the PWM is get stuck. You may try a "crowbar solution by using a watchdog which gets reseted in the ISR.

 

[Mondan]

I plan to build this but with an external A / D converter.

Can you tell me what cheap A/D converter can I use?
Or what are the characteristics of an acceptable quality for music A/D converter?

How can I get a PWM with better resolution? With an IC not with synchronized PWMs

The PIC 30F2020 has 16 PWM fast but is 4 times more expensive.
Is It Correct What Do I Write? Attiny at 20MHz = 20 M Instructions per second

Pic30F2020 at 120MHz = 30 M Instructions per second

 

[Mondan]

This is my first foray into class D amplifiers. It is an implementation of Dimitrov's ATTiny based design which can be found here. I modified the code a bit to remove a DC offset and programmed it with the Arduino IDE.

My circuit has a high pitched noise problem, but otherwise seemed to do a decent job.

Please tell me, answer me:
-
I have made the amplifier with Attiny25 but it has great noise. The program was written by me and it is quite simple.


Attiny25 / 45/85 has several modes of sleep.
One of sleep mode is for reduce ADC noise



I do not know if I use this type of sleep, because I tried to set it up and I do not know if it was set correctly.

This may be the reason why he has such a big noise?

You could also post, please, the HEX file, because I have an Atmel programmer