Uses the I2S module to synthesize tones using a minimal amount of Flash memory, RAM and CPU time.
Audio is output via the I2S_TX_DATA pin using Delta-Sigma modulation. This is a high-frequency bitstream which requires low-pass filtering and suitable amplification for driving speaker/headphones.
Warning
Do not connect the output directly to a loudspeaker or headphone as you may damage the GPIO. Always buffer the signal using a transistor, op-amp, etc.
See :component-esp8266:`driver` for further information about I2S.
As the output pin is normally used as UART0 RX, the alternate UART pin configuration is used:
| GPIO | Alternate | NodeMCU | Notes |
|---|---|---|---|
| 3 | I2S_TX_DATA | D9 | Audio output |
| 13 | RXD2 | D7 | Debug serial input |
| 15 | TXD2 | D8 | Debug serial output |
GPIO3 is still required for programming so you'll need to make sure the audio buffer is disconnected, or has a reasonably high impedance load. You'll also need an additional USB-serial converter connected to GPIO13 & 15 for terminal operation.
.. doxygenclass:: ToneGenerator :members:
.. doxygenclass:: ToneBuffer :members:
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