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Thread: Audio Shiled and MCP23017

  1. #1

    Audio Shiled and MCP23017

    I have a musical instrument project with a Teensy 3.5 and an audio shield. I need more inputs and am connecting a I2C chip (MCP23017). From my research both the audio shield and I2C chip use pins 18 (SCA) and 19 (SCL) on the Teensy. Is it OK for both of the devices (audio shield and I2C chip) to be connected to the same pins? The program I am running is basically PJRC's SamplePlayer, but with more inputs.
    Last edited by ofishal; 08-24-2019 at 05:37 PM.

  2. #2
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Ayer Massachussetts
    Yes, you should be able to use a MCP23017, as long as you avoid i2c addresses 0xA and 0x1A. I2C is a shared bus system, where each device has its own address, and it typically ignores data to/from other devices on the bus.

    Since the MCP23017's that I seen (mostly from Adafruit) can use address in the range 0x20 through 0x27 depending on the address pin settings, there should be problem with both on the bus. You do want to keep the wires as short as possible. Since the Audio shield has pull-up resistors, you won't need to add additional pull-up resistors to the i2c bus. Generally, you would want to run the MCP23017 at 3.3v like the Teensy and Audio Shield run at.

  3. #3
    Senior Member ETMoody3's Avatar
    Join Date
    Mar 2014
    New Ulm, Mn
    Works fine.

    I have a T3.6 \audio shield based multi effect box with pedalboard, the pedalboard has the MCP23017 chip in it, on the end of 10 ft of cord, running happy at 3.3 v.

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