RingTone Player


You may find the need to include basic audio features such as haptic feedback or tune generation to support an existing application. The advantage of using I2S for this is the very low CPU overhead.

This sample demonstrates how simple audio can be added to an application using the I2S ToneGenerator and RingTone libraries. The sample contains a selection of tunes.

The sample may be controlled via serial terminal, or by web interface.

Serial connection

Because I2S uses the serial RX pin, the serial port uses the alternate pin mappings. See Tone Generator for connection details.

You’ll still need the regular serial port for programming. Here’s a sample setup for Windows:

  • Using NodeMCU with standard serial port connected to COM4

  • Second USB/UART converter connected to alternate serial pins as COM8

The command line to build, flash and open a terminal would be:

make flashinit
make flash

Web interface

This is built using Bootstrap 4.3.1 and jQuery 3.4.1.

img-reboot Reboot

Un-installs the I2S driver then restarts the system after 5-seconds. The memory consumption drops as the DMA buffers are de-allocated.

img-play Play controls
▢ Stop

Tune playback stops at the current position, and the I2S driver is stopped so I2S interrupts are disabled. DMA buffers remain allocated.

|| Pause

Tune playback stops at the current position, but I2S interrupts remain active.

▷ Play

Resumes tune playback from stop/pause states.

img-mode Voice and Mode

Selects available voice for the tone generator (Sine, Triangular, Sawtooth or Square wave).

Playback mode

  • ⇢ Sequential

  • 🔀 Random

Playback speed


Tune selection

↤ Previous

Play previous tune

↲ Rewind

Rewind to start of current tune

↦ Next

Play next tune

→ Skip

Skip to a random tune


Shows the current tune and elapsed play time. A drop-down list shows all available tunes.


In addition to play controls, there are three graphs showing some statistics over a two-minute period. The data is sent from the ESP8266 via websocket once per second.

CPU Usage
CPU Usage graph

Gives an indication of processor loading. Try connecting a second web client to see what happens.

Fill Time
Fill time graph

Shows the time taken by the Tone Generator to create and buffer tone waveforms.

This graph has three traces, indicating time in milliseconds over the 1-second update period:

  • Red: Longest time taken

  • Green: Shortest time

  • Black: Average time

You’ll see more activity during complex, fast tunes but also for lower notes which require more samples (and larger buffers).

The progress bar indicates the total time taken over the update period.

Memory Usage
Memory usage graph

The graph has three traces:

  • Black: Available memory

  • Red: Maximum memory used during the update period

  • Green: Memory in use at the time of update

The red/green traces generally follow each other and represent the allocation/deallocation of tone buffers.


SoC support

  • esp8266

  • host