Just to be clear:
The following pins are common pins, used by both the audio board and available for other uses:
- Vin (I'm not sure if the audio shield uses this or not)
- Analog Ground (used for the audio parts)
- 3.3v
- normal Ground (used for the SPI parts)
The following pins are used by the audio board for I2C, which can by used by other devices, as long as you don't use devices with addresses 0x0A or 0x1A. I2C is a shared bus system for attaching other devices using SCL, SDA, 3.3v, and normal ground. Each device has an address that it listens on:
- Pin 18/A4 (SDA)
- Pin 19/A5 (SCL)
The following pins are used by the audio for SPI, which can be used by other devices as long as you use a different CS (chip select) pin. SPI is a shared bus system for attaching other devices using SCK, MOSI, MISO, 3.3v, and normal ground as common pins. Each device has a separate pin that controls whether the device is active or not (plus possibly some other pins that are not common). Note on the 3.2/3.5/3.6, you must use the alternate versions of SPI pins, because the pins overlap with the I2S audio pins. If you don't want to use the micro SD card or haven't soldered on a memory chip, you don't have to connect these pins to the audio board. However, if you use a SPI device like a display, you will need to use the alternate pins. Given the 3.6 has its own micro SD card (which is faster than the card in the audio shield), and the audio shield does not come with flash memory soldered on, you likely won't need to use the SPI pins.
- Pin 6 (CS pin for flash memory)
- Pin 7 (alternate MOSI pin)
- Pin 10 (CS pin for the micro SD card)
- Pin 12 (MISO pin)
- Pin 14 (alternate SCLK pin)
The following pins are used for audio input/output to the audio shield, and must be connected, and not otherwise used:
- Pin 9 (I2S BCLK)
- Pin 11 (I2S MCLK) -- this is the normal SPI MOSI pin
- Pin 13 (I2S RX) -- this is the normal SPI SCLK pin
- Pin 22/A8 (I2S TX)
- Pin 23/A9 (I2S LRCLK)
The following pin is on the audio board for attaching a potentiometer (presumably for using to control volume). It has extra resistors and/or capacitors that means you probably should only use it for
analogInput and not as a digital input/ouptut pin, even if you don't use it for volume:
The following pins are not used by the audio shield:
- Pins 0-5
- Pin 8
- Pins 20/A6 and 21/A7
- Pins 16/A2 and 17/A3
- Pins A10, A11, AREF, VUSB
- Pins A21/DAC0 and A22/DAC1
- All other pins > 23
- Reset, Program, Vbat
One way to do this is to use stacking headers on the audio shield. You would cut the board so it has 24 pins, soldering the first 14 pins to the audio shield on each side, leaving the remaining 10 pins for the extra pins in the Teensy 3.6 to connect with the breadboard. That way, you attach the Teensy on top, the audio shield in the middle, and a breadboard (or prototype board) on the bottom: