This audio adaptor lets you easily add high quality 16 bit, 44.1 kHz sample rate (CD quality) audio to your projects with Teensy 4.0, 4.1. It supports stereo headphone and stereo line-level output, and also stereo line-level input or mono microphone input.
An advanced audio library lets you use the input and output simultaneously together with a toolkit of audio processing objects, to easily create all types of sophisticated audio applications. You can play multiple sound files, create synthesized waveforms, apply effects, mix multiple streams and output high quality audio to the headphones or line out pins.
Teensy 4.x with Cortex-M7 provides even more DSP capability, allowing sophisticated synthesis applications to create many simultaneous “voices” or effects.
Signals to Teensy
The audio chip, part number (SGTL5000), connects to Teensy using 7 signals. The I2C pins SDA and SCL are used to control the chip and adjust parameters. Audio data uses I2S signals, TX (to headphones and/or line out) and RX (from line in or mic), and 3 clocks, LRCLK (44.1 kHz), BCLK (1.41 MHz) and MCLK (11.29 MHz). All 3 clocks are created by Teensy3. The SGTL5000 operates in “slave mode”, where all its clock pins are inputs.
The SD socket is accessed with 4 SPI pins. SCLK and MOSI are used at alternate locations. See the audio library examples for details on how to select these different pins. The SD card is useful for playing music. Sandisk and other good quality SD cards are capable of playing 2 WAV files simultaneously.
An optional W25Q128FV flash memory chip (not populated) on the bottom side is also accessed using SPI, with the MEMCS pin to select the chip. Future versions of the audio library may use this low latency flash memory for short audio clips or wavetable synthesis. Currently there is no software support for this chip.
The line in/out header uses a pinout compatible with the AC97 audio header on PC motherboards. The front panel cables from most PCs can be connected, or wires can be soldered directly to the pins.
Note: Do not connect HP_VGND to system ground, even when unused. This is a virtual ground (DC voltage) that should never connect to an actual “0 Volt ground”. Use the widest, shortest trace possible for the HP_VGND.
Additional technical details can be found on the manufacturer’s webpage – PJRC Audio Adaptor Boards for Teensy 3.x and Teensy 4.x