Arduino tone() just got 8-bit volume control!*

*with no extra components!

VIDEO DEMONSTRATION

Ever needed a project to play a tone through a speaker or piezo that wasn't blisteringly loud? You can bring the volume down with a resistor, but what if you needed a loud alert beep at some point as well?

Now it's no longer an issue. :) Using ultrasonic PWM, the Volume library allows the speaker itself to act as an RC filter to produce smooth (8-bit) analog-like volume control.

Contents

• Installation
• Usage
• Functions
• Supported Pins
• Limitations
• Volume Library Comparison
• Contributing
• License and credits

Installation

With Arduino Library Manager:

1. Open Sketch > Include Library > Manage Libraries in the Arduino IDE.
2. Search for "Volume", (look for "Connor Nishijima") and select the latest version.
3. Click the Install button and Arduino will prepare the library and examples for you!

Manual Install:

1. Click "Clone or Download" above to get an "arduino-volume-master.zip" file.
2. Extract it's contents to the libraries folder in your sketchbook.
3. Rename the folder from "arduino-volume-master" to "Volume".

Usage

Using the volume-controlled vol.tone() function looks very similar to the Arduino tone(), but the function arguments are very different:

Arduino:

• tone(unsigned int pin, unsigned int frequency);

Volume:

• vol.tone(unsigned int frequency, byte volume);

Volume control is limited to certain pins. See Supported Pins.

Here is what you need to get started with the bare minimum:

#include "Volume.h" // Include the Volume library

Volume vol; // Plug your speaker into the default pin for your board type:
// https://github.com/connornishijima/arduino-volume1#supported-pins

void setup() {
  vol.begin();
}
void loop() {
  byte volumes[4] = {255, 127, 12, 0};   // List of volumes: 100% Volume, 50% Volume, 5% Volume, 0% Volume
  for (int i = 0; i < 4; i++) { // Iterate through volume list one second at a time
    vol.tone(440, volumes[i]);
    vol.delay(1000);
  }

  vol.tone(880, 255); // 100% Volume
  vol.fadeOut(5000);  // Start a 5 second fade out
  vol.delay(5000);    // Wait for this fade to finish
}

Of course, you can set the volume to any value between 0 and 255 you'd like, for full 8-bit volume fades.

Functions

Volume vol;

This initializes the Volume library after import. "vol" can be any word you want, as long as it's reflected in the rest of your code.

vol.begin();

This sets up a Timer Compare Interrupt on Timer1 for the tone frequencies. (You won't hear anything until a vol.tone() is called.)

vol.setMasterVolume(float percentage);

This is a multiplier applied to the volume of any tones played. By default this is 1.00 - a value of 0.34 would make all tones 34% of their programmed volume;

vol.tone(unsigned int frequency, byte volume);

This is where the magic happens. At the frequency you specify, your Arduino will analogWrite(volume) to the speaker with a PWM frequency of 62.5KHz, for half the duration of a single period of the frequency before pulling it LOW. (Using Timer1 compare-match interrupts to maintain the input frequency) This high-speed PWM is beyond your range of hearing, (and probably the functioning range of your speaker) so it will just sound like a quieter or louder version of the input frequency!

vol.fadeOut(unsigned int duration);

This will cause the currently playing tone to fade out over the duration specified in milliseconds.

vol.noTone();

This is identical in function to the standard noTone() function, this stops any currently playing tones.

vol.delay(); vol.delayMicroseconds(); vol.millis(); vol.micros();

These are replacements to the standard time-keeping Arduino functions designed to compensate for the changes in the Timer0 clock divisor. See Limitations.

vol.end();

This stops any currently playing tones, and resets Timer0 to it's default functionality. Creative use of vol.begin() and vol.end() can usually resolve conflicts with other libraries or functions that might need Timer0 (volume) or Timer1 (frequency) to be in their usual settings.

vol.alternatePin(bool enabled);

This causes the AVR to use the ALTERNATE_PIN defined in the Supported Pins section for sound production.

Supported Pins

By default, the library uses DEFAULT_PIN for the speaker, (changes from board to board due to Timer0 channels) but if you need this pin for digitalWrite's, you can call vol.alternatePin(true) to use ALTERNATE_PIN instead.

*I recently killed my only ATmega32u4 board while stripping it for low-power usage and don't have one to test current releases of the library. If anyone who has a working one wants to report compatibility back to me, please do so as I've only tested the initial release!

Limitations

Unfortunately, cheating the Arduino's normal functions in this way means we'll lose some of them. This is also still a proof-of-concept library at this point, so it may break more functionality than I'm aware of. Sorry!

16MHz Only:

I haven't programmed in options for 8MHz boards yet, though if you want to use one, just replace all occurrences of "16000000" in the library files with "8000000" and it may work.

Automatic detection of CPU speed was added in version 1.0.2!

ATmega Only:*

I don't know if I'll have this working on ATTiny*5 boards any time soon, though it's theoretically possible on any AVR with >= 2 timers. For now, it's only confirmed working on Arduino Uno (ATMega168/328) and Mega. (ATMega1280/2560)

Volume is limited to pins 5 & 6:

This is because only pins 5 & 6 are driven by Timer0, which can do PWM at a frequency higher than your hearing range! This is the main trick behind the volume function. It also means that while you're using Volume, normal analogWrite() use probably won't work on these two pins.

Now that the Mega168, 328, 1280, 2560, 16u2/32u4 and more are now supported, the supported pins differs from board to board. See Supported Pins section.

Volume alters Timer0 for 62.5KHz PWM:

Speaking of Timer0 - it's normally used for the delay(), delayMicroseconds(), millis() and micros() functions. Normally with Timer0 set with a divisor of 64, delay(1000) would wait for 1 second - but because Volume sets Timer0 with a divisor of 1, delay(1000) will now only wait for 15.625ms! But don't worry. Volume provides alternative vol.delay(time) and vol.delayMicroseconds(time) functions with the math fixed for you. This new divisor is necessary to drive PWM at 62.5KHz, faster than you can hear.

Volume does not yet offer fixed millis() or micros() functions:

I haven't gotten around to toying with these yet. If you need to use millis() or micros() BETWEEN playing sounds, just use a vol.end() to reset Timer0 to it's default function, and vol.begin() to use it for Volume again after you're done.

Version 1.1.1 added proper millis() and micros() support! See Functions.

Volume Library Comparison

Now that there are three separately-developed Volume libraries, here is a table delineating their abilities. One will be good for higher frequencies, one will do custom waves, one will have higher volume accuracy, and so forth. Eventually I'm looking to merge them, but for now each has it's strengths and weaknesses.

Contributing

As I've only written one library before for my own use, I'm still new to this! Any advice or pull requests are welcome. :)

License and Credits

Developed by Connor Nishijima (2016)

Special Thanks to Andrew Neal (For putting up with the incessant and inconsistent artificial "cricket-duino" hidden in his vent that I developed this library for.)

Released under the GPLv3 license.