The document describes how to set up an Arduino Uno to play differential audio using pulse-width modulation (PWM) on pins 3 and 11. It configures timer 2 for fast PWM mode on both pins, with non-inverting PWM on pin 3 and inverting PWM on pin 11. It also configures timer 1 in CTC mode to generate an interrupt at the sample rate for audio playback.

1. ‫الکریم‬ ‫رسولہ‬ ‫علی‬ ‫نصلی‬ ‫و‬ ‫نحمدہ‬
‫الرجیم‬ ‫الشیطن‬ ‫من‬ ‫باہلل‬ ‫اعوذ‬
‫الرحیم‬ ‫الرحمن‬ ‫ہللا‬ ‫بسم‬

2. ‫الکریم‬ ‫رسولہ‬ ‫علی‬ ‫نصلی‬ ‫و‬ ‫نحمدہ‬
‫الرجیم‬ ‫الشیطن‬ ‫من‬ ‫باہلل‬ ‫اعوذ‬
‫الرحیم‬ ‫الرحمن‬ ‫ہللا‬ ‫بسم‬
Arduino Uno (ATmega328P )
Differential audio playback using PWM on pin 3 and 11

3. Use internal clock
ASSR &= ~(_BV(EXCLK) | _BV(AS2));

4. Set fast PWM mode
TCCR2A |= _BV(WGM21) | _BV(WGM20);
TCCR2B &= ~_BV(WGM22);
√

5. Non-inverting PWM on OC2A
TCCR2A = (TCCR2A | _BV(COM2A1)) & ~_BV(COM2A0);

6. Inverting PWM on OC2B
TCCR2A = TCCR2A | _BV(COM2B1) | _BV(COM2B0);

7. No prescaler selected for timer 2
TCCR2B = (TCCR2B & ~(_BV(CS22) | _BV(CS21))) | _BV(CS20);
√

8. Set CTC mode for timer 1

9. TCCR1B = (TCCR1B & ~_BV(WGM13)) | _BV(WGM12);
TCCR1A = TCCR1A & ~(_BV(WGM11) | _BV(WGM10));
√

10. TCCR1B = (TCCR1B & ~(_BV(CS12) | _BV(CS11))) | _BV(CS10);
√

11. • // Set the compare register (OCR1A).
• // OCR1A is a 16-bit register, so we have to do this with
• // interrupts disabled to be safe.
• // 16MHz / 8kSamplesPerSec = 2000
• OCR1A = F_CPU / SAMPLE_RATE;