noTone()

Abstract

The noTone() stops the output of square wave began by tone().

Checks the timer/counter number using by tone() and stops it.

Souce Code

The noTone() is defined in hardware/arduino/avr/cores/arduino/Tone.cpp

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#define AVAILABLE_TONE_PINS 1
 
// Leave timer 0 to last.
const uint8_t PROGMEM tone_pin_to_timer_PGM[] = { 2 /*, 1, 0 */ };
static uint8_t tone_pins[AVAILABLE_TONE_PINS] = { 255 /*, 255, 255 */ };
 
void noTone(uint8_t _pin)
{
  int8_t _timer = -1;
   
  for (int i = 0; i < AVAILABLE_TONE_PINS; i++) {
    if (tone_pins[i] == _pin) {
      _timer = pgm_read_byte(tone_pin_to_timer_PGM + i);
      tone_pins[i] = 255;
      break;
    }
  }
   
  disableTimer(_timer);
 
  digitalWrite(_pin, 0);
}

The AVAILABLE_TONE_PINS is set to 1. This is the number of pins that can be used at the same time.

The tone_pin_to_timer_PGM[] is an array that holds timer/counter. Currently only “2” is defined.

The tone_pins[] shows pins which is used by timer/counter, which is related to tone_pin_to_timer_PGM[].

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#define AVAILABLE_TONE_PINS 1
 
// Leave timer 0 to last.
const uint8_t PROGMEM tone_pin_to_timer_PGM[] = { 2 /*, 1, 0 */ };
static uint8_t tone_pins[AVAILABLE_TONE_PINS] = { 255 /*, 255, 255 */ };

The input is _pin and its type is uint8_t. There is no output.

Checks if the specified _pin is used. If found, set the timer number to _timer then sets tone_pins[i] to 255 which means unused.

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void noTone(uint8_t _pin)
{
  int8_t _timer = -1;
   
  for (int i = 0; i < AVAILABLE_TONE_PINS; i++) {
    if (tone_pins[i] == _pin) {
      _timer = pgm_read_byte(tone_pin_to_timer_PGM + i);
      tone_pins[i] = 255;
      break;
    }
  }

The pgm_read_byte() is a macro to read one byte from PROGMEM. As the tone_pin_to_timer_PGM is an array, tone_pin_to_timer_PGM+i means the i-th element of the array.

It calls disableTimer() to stop the timer. Then it calls digitalWrite() to stop the output to digital pin.

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  disableTimer(_timer);
 
  digitalWrite(_pin, 0);
}

At the last it calls digitalWrite(), so the pin which is not used by tone() is specified, the output to the pin is stopped.

Version

Arduino AVR Boards 1.8.6

License

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/*
  Copyright (c) 2019 garretlab.
  Added source code explanation by garretlab.
*/

/* Tone.cpp

  A Tone Generator Library

  Written by Brett Hagman

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

Version Modified By Date     Comments
------- ----------- -------- --------
0001    B Hagman    09/08/02 Initial coding
0002    B Hagman    09/08/18 Multiple pins
0003    B Hagman    09/08/18 Moved initialization from constructor to begin()
0004    B Hagman    09/09/26 Fixed problems with ATmega8
0005    B Hagman    09/11/23 Scanned prescalars for best fit on 8 bit timers
                    09/11/25 Changed pin toggle method to XOR
                    09/11/25 Fixed timer0 from being excluded
0006    D Mellis    09/12/29 Replaced objects with functions
0007    M Sproul    10/08/29 Changed #ifdefs from cpu to register
0008    S Kanemoto  12/06/22 Fixed for Leonardo by @maris_HY
0009    J Reucker   15/04/10 Issue #292 Fixed problems with ATmega8 (thanks to Pete62)
0010    jipp        15/04/13 added additional define check #2923
*************************************************/

Last Update

July 31, 2025