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Thread: Prop Shield

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    Prop Shield

    Can the Prop Shield be used at the same time as the Audio Shield?

    I need the LED driver and the audio amp from the Prop Shield as well as stereo audio in and stereo audio out.

  2. #2
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by bdoan View Post
    Can the Prop Shield be used at the same time as the Audio Shield?

    I need the LED driver and the audio amp from the Prop Shield as well as stereo audio in and stereo audio out.
    Not without a lot of work. And note, the audio amp in the prop shield only works with the built-in DAC on the Teensy 3.2 (or 3.5/3.6 if you add a wire from the DAC0 pin to the prop shield).

    In terms of specifics:
    • The audio shield for the Teensy 3.x chips (revision C) changes the SPI pins 11 and 13 to use the alternate pins (7, 14 respectively) because 11 and 13 are used by the I2S sub-system. The prop-shield uses pins 11 and 13 for the LED driver. So you basically can't use both audio and the LED driver on Teensy 3.x. Note, pin 7 is the LED enable pin on the prop shield.
    • The audio shield for the Teensy 4.x chips (revision D) does not change the SPI pins. So in theory, you can use the LED driver. However, if you use any SPI device on the main bus (i.e. the SD card reader in the audio shield, the persistent flash memory chip soldered onto the audio shield, or any other SPI device like a display, you will have to manually switch pins 11 and 13 from being normal data pins to SPI pins.
    • As I mentioned, the prop shield uses the DAC (digital -> analog) pin for doing lower quality audio. This is separate from the stereo higher quality audio that the audio shield uses. The amplifier only works with the DAC shield. Note, the Teensy 4.x chips DO NOT have a DAC, so you would not be able to use the DAC and the amplifier. The Teensy 3.5/3.6 have 2 DACs, but they are in a different location from the Teensy 3.2, so you would have to run a wire from DAC0 to the prop shield to use it.


    Rather than trying to use the prop shield, I think you need to use a separate circuit to bring the power from the data pin from 3.3v to 5v. However, if you are using 2812B LEDs (what Adafruit calls Neopixels), the leds have strict timing requirements, and you need to use a fast enough voltage shifter. Thie 74HCT125 chip is generally used for this shifting (or some of the variants):


    Likewise for the amplifier, it is typically better to use a separate amplifier. There are many different amplifiers. One simple one is:


    Where you want to use the prop shield is for simple things where you have some number of LEDs, and mono output and are using the Teensy 3.x systems. I have used it for doing costumes wtih LEDs and sounds.

    Where you want to use the audio shield is if your sound processing requirements are higher, including using stereo.

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