Amp Sound from Attiny85

Other Hardware Audio
1

Hello,

Ive been playing around recently with David Johnson-Davies script on looping a sound from an Attiny85. I replaced his values with an appropriately scaled 0-255 sound outputs from my own wav file. Sound loops great from the Attiny85, but it is very quiet. Looking at the original code, its like its turning the 85 into its own mini Class D amp. Is there a way based on the code and the circuit to amp the signal with an external class D mono amp? Ive added the sketch and circuit below.

cicuit1
cicuit1423×234 13.7 KB

/* Audio Sample Player v2

   David Johnson-Davies - www.technoblogy.com - 23rd October 2017
   ATtiny85 @ 8 MHz (internal oscillator; BOD disabled)
      
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

/* Direct-coupled capacitorless output */

#include <avr/pgmspace.h>
#include <avr/sleep.h>
#define adc_disable()  (ADCSRA &= ~(1<<ADEN))

// Audio encoded as unsigned 8-bit, 8kHz sampling rate
const uint8_t scanner_wav[] PROGMEM = {
124,116, 115, 117, 124, 131, 136, 135, 134, 125, 117, 114, 115, 120, 128,142, 150,
156, 152, 141, 125, 106, 92, 90, 101, 118, 139, 156, 164, 160, 148, 131,118,
107, 107, 110, 119, 130, 138, 141, 136, 128, 120, 110, 112, 117, 128,143, 154,
157, 151, 138, 120, 100, 90, 89, 100, 117, 137, 157, 165, 162, 152, 136,119,
105, 100, 102, 115, 128, 141, 145, 142, 133, 123, 113, 111, 114, 123,137, 148,
157, 152, 143, 127, 110, 97, 91, 97, 110, 127, 145, 158, 163, 160, 148,135,
118, 105, 103, 103, 111, 123, 132, 141, 143, 139, 135, 126, 119, 119,120, 129,
139, 147, 148, 141, 132, 117, 104, 97, 97, 107, 123, 141, 157, 165, 163,150,
135, 119, 104, 95, 98, 108, 119, 133, 145, 147, 144, 132, 123, 119, 121,128,
136, 144, 146, 137, 125, 112, 99, 94, 100, 112, 128, 147, 163, 168, 164,148,
132, 112, 99, 93, 101, 111, 124, 138, 145, 145, 136, 128, 124, 125, 130,138,
146, 145, 138, 126, 109, 95, 92, 98, 111, 128, 149, 162, 169, 162, 151,133,
117, 103, 95, 96, 108, 120, 132, 140, 140, 136, 132, 130, 132, 138, 145,144,
140, 130, 115, 99, 90, 93, 105, 121, 141, 156, 167, 165, 155, 142, 125,112,
106, 101, 106, 114, 120, 124, 128, 129, 133, 137, 144, 153, 153, 151,140, 127,
107, 93, 86, 90, 104, 124, 148, 164, 169, 163, 150, 133, 120, 109, 105,108,
113, 118, 123, 126, 124, 126, 128, 137, 144, 152, 153, 148, 137, 121,105, 93,
90, 97, 113, 130, 146, 157, 159, 156, 148, 136, 124, 113, 108, 106, 108,113,
121, 126, 131, 135, 137, 139, 143, 145, 144, 139, 133, 122, 110, 102,99, 103,
114, 128, 141, 151, 157, 156, 145, 135, 124, 114, 108, 109, 114, 120,125, 130,
131, 129, 130, 132, 136, 142, 145, 143, 136, 125, 112, 102, 100, 103,117, 130,
144, 153, 151, 147, 136, 125, 117, 118, 119, 123, 126, 126, 126, 123,118, 120,
123, 128, 137, 143, 148, 148, 139, 129, 117, 105, 101, 103, 113, 129,144, 151,
149, 144, 132, 121, 115, 115, 124, 129, 137, 137, 133, 122, 116, 110,112, 123,
138, 147, 153, 151, 140, 127, 111, 105, 104, 109, 121, 135, 146, 149,143, 136,
124, 114, 111, 118, 127, 138, 144, 139, 132, 120, 107, 103, 113, 124,141, 153,
154, 147, 133, 118, 107, 104, 111, 124, 137, 145, 144, 139, 125, 118,
112, 117,126, 135, 144, 148, 140, 130, 118, 106, 106, 110, 121, 137, 147, 153,148, 137,
122, 111, 104, 110, 123, 136, 145, 143, 138, 126, 113, 108, 112, 123,136, 148,
149, 144, 131, 116, 106, 105, 110, 125, 138, 148, 149, 143, 131, 118,109, 109,
115, 128, 140, 146, 144, 136, 124, 112, 105, 109, 122, 137, 148, 151,145, 133,
117, 106, 106, 115, 129, 143, 148, 146, 131, 119, 107, 109, 120, 135,144, 152,
145, 131, 115, 106, 106, 114, 131, 145, 152, 146, 133, 118, 110, 107,116, 130,
144, 149, 144, 131, 115, 106, 104, 116, 133, 149, 154, 146, 130, 109,100, 105,
119, 139, 155, 158, 144, 124, 104, 97, 105, 123, 144, 160, 156, 139,117, 100,
100, 114, 134, 153, 159, 147, 124, 103, 93, 104, 126, 149, 162, 158,138, 113,
95, 96, 113, 139, 156, 157, 145, 122, 102, 95, 108, 129, 151, 159, 152,131,
109, 96, 98, 117, 142, 158, 158, 144, 123, 102, 94, 103, 124, 146, 159,156,
141, 122, 102, 99, 107, 126, 146, 153, 153, 137, 120, 102, 102, 111,129, 145,
156, 151, 137, 118, 104, 100, 110, 127, 147, 154, 152, 137, 118, 104,100, 112,
131, 151, 157, 147, 130, 112, 102, 106, 120, 138, 150, 152, 141, 124,113, 106,
110, 121, 137, 146, 146, 136, 128, 118, 110, 111, 118, 131, 141, 145,140, 131,
121, 111, 109, 115, 130, 142, 148, 144, 134, 118, 106, 107, 115, 131,148, 153,
144, 131, 115, 104, 107, 120, 138, 150, 151, 140, 126, 110, 101, 108,126, 145,
154, 151, 137, 119, 105, 102, 111, 132, 150, 155, 147, 132, 113, 99,103, 118,
137, 151, 153, 143, 124, 110, 103, 108, 124, 141, 151, 146, 138, 122,109, 105,
111, 125, 138, 150, 149, 141, 126, 113, 104, 109, 119, 134, 146, 149,142, 130,
118, 107, 107, 117, 129, 144, 149, 148, 138, 123, 108, 105, 108, 122,138, 150,
150, 144, 130, 115, 106, 106, 116, 131, 143, 152, 151, 139, 125, 109,99, 105,
116, 137, 152, 157, 151, 137, 117, 102, 98, 108, 125, 143, 154, 153,141, 124,
109, 102, 107, 121, 135, 147, 149, 142, 129, 117, 107, 109, 119, 131,141, 142,
140, 130, 122, 116, 117, 124, 131, 136, 136, 133, 128, 121, 119, 123,127, 134,
135, 134, 128, 122, 122, 121, 127, 134, 139, 139, 133, 124, 116, 114,116, 123,
134, 140, 145, 144, 134, 123, 114, 108, 110, 118, 129, 143, 148, 147,140, 126,
115, 106, 105, 113, 126, 138, 150, 150, 144, 134, 121, 111, 103, 106,115, 127,
139, 152, 153, 147, 134, 119, 106, 98, 104, 116, 131, 147, 157, 155,146, 131,
115, 101, 99, 103, 117, 136, 151, 157, 153, 141, 127, 112, 104, 103,112, 124,
140, 148, 152, 147, 135, 125, 113, 108, 110, 115, 128, 138, 146, 146,143, 133,
123, 114, 109, 109, 116, 126, 139, 145, 148, 145, 133, 123, 112, 106,107, 116,
129, 140, 148, 151, 144, 129, 118, 108, 105, 111, 122, 134, 146, 150,148, 138,
123, 112, 105, 106, 116, 128, 143, 149, 151, 144, 133, 118, 108, 106,109, 117,
130, 143, 151, 150, 143, 130, 116, 108, 103, 108, 121, 134, 147, 150,146, 137,
126, 112, 107, 108, 117, 130, 141, 147, 146, 140, 128, 117, 110, 110,116, 127,
133, 142, 142, 137, 130, 125, 121, 118, 122, 122
};
unsigned int scanner_wav_len = 1019;
unsigned int p = 0;

void setup () {
  // Enable 64 MHz PLL and use as source for Timer1
  PLLCSR = 1<<PCKE | 1<<PLLE;     
 
  // Set up Timer/Counter1 for PWM output
  TIMSK = 0;                              // Timer interrupts OFF
  TCCR1 = 1<<PWM1A | 2<<COM1A0 | 1<<CS10; // PWM A, clear on match, 1:1 prescale
  GTCCR = 1<<PWM1B | 2<<COM1B0;           // PWM B, clear on match
  OCR1A = 128; OCR1B = 128;               // 50% duty at start

  // Set up Timer/Counter0 for 8kHz interrupt to output samples.
  TCCR0A = 3<<WGM00;                      // Fast PWM
  TCCR0B = 1<<WGM02 | 2<<CS00;            // 1/8 prescale
  TIMSK = 1<<OCIE0A;                      // Enable compare match
  OCR0A = 124;                            // Divide by 1000

  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  pinMode(4, OUTPUT);
  pinMode(1, OUTPUT);
}

void loop () { }

// Sample interrupt
ISR (TIMER0_COMPA_vect) {
  char sample = pgm_read_byte(&scanner_wav[p++]);
  OCR1A = sample; OCR1B = sample ^ 255;
  // End of data? Go to sleep
  if (p == scanner_wav_len) {
    p = 0;
    //TIMSK = 0;
    //adc_disable();
    //sleep_enable();
    //sleep_cpu();  // 1uA
  }
}
2

I moved your topic to an appropriate forum category @dylaninwv.

In the future, when creating a topic please take some time to pick the forum category that best suits the subject of your topic. There is an "About the _____ category" topic at the top of each category that explains its purpose.

This is an important part of responsible forum usage, as explained in the "How to get the best out of this forum" guide. The guide contains a lot of other useful information. Please read it.

Thanks in advance for your cooperation.

3

You need an amplifier. You can't directly drive a 4 or-8-Ohm speaker. You are over-stressing the device and the output voltage is probably dropping.

Just quickly checking the datasheet, the "absolute maximum" output current is 40mA. Ohm's Law says 3.3V / 0.04A = 85 Ohms minimum resistance/impedance. (And that's a bit more than 0.1 Watt.)

Class-D may not make sense if you don't need much power and you're not going to get much power unless you supply the amplifier with higher voltage.

Regular powered computer speakers will work, you can buy a small (or high-power) amplifier, or amplifier board, or TI makes lots of amplifier chips. The LM380 is a super-popular low-power amplifier chip.

The more you amplify, the more likely you are to notice the low-resolution of 8-bits. You'll hear quantization noise which is like a "fuzz" on top of the audio, most noticeable when the audio is quiet. If you have a low sample rate, the high frequencies will be limited, and there may be other noise unrelated to resolution.

Be careful with unfiltered PWM audio! It's NOT analog! Even when "silent" it's putting-out full-voltage high-frequency PWM. It can stress an amplifier. I wouldn't connect it to my home theater system or any amplifier that I cared about.

4

In this case fidelity is not an issue. Im helping someone build a fairy wand for a cosplay role, and the wand just makes a repetitive magical looping noise whenever there’s power. So it has to be small, run off of a 3.7 battery and a 20mm speaker. Size is an issue, far more than sound quality. and its a one shot deal as well. As I said, it does do what I need it to - just trying to upp the volume…

5

Try the LM386 or a little amplifier board. Before, I said LM380, which I uses a lot in the past, but the 386 is the one I was thinking of and it seems to be more popular now..

You'll probably need a volume control pot because you mainly need to boost the current & power, not the voltage. Most of these amplifiers and amplifier chips have voltage gain in the ballpark of 20dB (10X) and you've already got 3.3V or 3.7V peak-to-peak. You'll get clipping (distortion) if you've got voltage gain that you can't use.

Power will be limited by battery voltage more than the amplifier and it power be calculated as Wattage = Voltage Squared / Resistance. That's the RMS voltage, and 3.3V peak-to-peak is about 1.1V RMS so you'll be getting less than 1 Watt.

6

Since this is a digital signal, a power buffer on each ATtiny output might do the trick.
I'm thinking of a L9110 motor driver.
You won't hear the switching if the wave clock is high enough.

I did something similar with an ESP32. here.
An old closed-back 8 Ohm midrange speaker gave the loudest sound without amplification.
Leo..

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