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Thread: Available Teensy 4.0 pins when Audio shield D attached

  1. #1

    Available Teensy 4.0 pins when Audio shield D attached

    I have an audio shield (D) soldered pin for pin to a Teensy 4.0 in such a fashion that the pins go down thro to the breadboard.
    Which Teensy pins, if any, are not interfered with by the audio shield and so, being isolated, are available for use by digital and
    analog i/o connections ?

  2. #2
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    This PJRC product page should show the answers:

    Those noted pins include SPI - which may not be in use … And the same for Pin #15 tied to Pot on the Audio board.

  3. #3
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Ayer Massachussetts


    I thought I had done a post, but it turns out that was for the Audio board for the 3.x series. Here is the information for the 4.0:

    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);
    • Ground pins (the ground pin between Vin and 3.3v is used for the audio bits, the ground pin next to pin 0 is used for the SPI bits);
    • 3.3v

    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. The audio board provides pull-up resistors, so you don't need to add additional resistors:
    • Pin 18/A4 (SDA)
    • Pin 19/A5 (SCL)

    The following pins are used by the audio for SPI (flash memory, micro SD card reader), 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). 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. While the audio board has a place to solder a flash memory card, it doesn't come with a flash memory card installed on the board.

    If you use a SPI device, you will need to use alternate CS (and possibly D/C, reset, etc.) pins from pins 6 and 10. Unlike the 3.x Teensys, there is only one pin (10) that is special to the hardware, so the advanced display drivers can't use the techniques that were used in the 3.x Teensys to optimize some displays.

    • Pin 6 (CS pin for flash memory)
    • Pin 10 (CS pin for the micro SD card)
    • Pin 11 (MOSI pin)
    • Pin 12 (MISO pin)
    • Pin 13 (SCLK pin)

    If you are connecting SPI devices (such as displays), you might want to read this:

    The following pins are used for audio input/output to the audio shield, and must be connected, and not otherwise used:
    • Pin 7 (I2S OUT1A)
    • Pin 8 (I2S IN1)
    • Pin 20/A6 (I2S LRCLK1)
    • Pin 21/A7 (I2S BCLK1)
    • Pin 23/A9 (I2S MCLK1)

    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 for smoothing out analog input. That means you probably should only use it for analogInput and not as a digital input/ouptut pin, even if you don't use the 3 pins on the audio board:
    • Pin 15/A1

    The following pins are not used by the audio shield:
    • Pins 0-6
    • Pin 9
    • Pin 14/A0
    • Pins 16/A2 - 17/A3
    • Pin 22/A8

    There are other pins that don't connect to holes in the audio shield:
    • Solder pads connecting pins above 23 on the bottom of the Teensy (i.e. pins 24-33 in the back of the Teensy, and pins 34-39 at the front of the Teensy).
    • The 5 pins at the back (On/off, Program, Ground, 3.3v, and Vbat).

    There are at least 5 different methods of getting at the bottom pins being discussed in the General forum.
    Last edited by MichaelMeissner; 11-10-2019 at 10:54 PM.

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