Tone Generator

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 Esp8266 Drivers 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.

References

Used by