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Thread: Lots of noise! Teensy 4 with audio shield, battery powered

  1. #1
    Junior Member
    Join Date
    Jun 2015
    Posts
    16

    Lots of noise! Teensy 4 with audio shield, battery powered

    Hi!

    I work with a Teensy 4, an audio shield, an amplifier and a Benewake TFMINI-S Micro LIDAR (UART), 18V battery and 2 step down regulators (step down to 12V for the amplifier and 5V for the Teensy). I am playing a sound from the SD card and change the volume with the LIDAR. I get lots of noise, a hiss and kind of a square wave tone.

    • When I don't use the amplifier and use headphones, I have no noise.
    • When I use a power supply instead of the battery, it does not stop the noise.
    • When I unplug the LIDAR and play some sounds from the SD some of the noise stops, but not all of it.
    • When I use two batteries (one for the Teensy, one for the amplifier), I have no noise.
    • When I use two batteries but link the Teensy's ground to the amplifier's ground, some of the noise is back
    • When I play a hardware test beep (no SD, no LIDAR), I have no noise.
    • I tried a couple of different step down regulators with the same result. This one and this one


    Any idea of what can cause that noise and what I could do to stop or filter that noise?

    Thank you!

  2. #2
    Senior Member
    Join Date
    Jul 2020
    Posts
    1,762
    The step down regulator is likely the predominant source of the noise (I presume its a switch-mode converter). I suggest using a clean supply for the amplifier not shared with anything digital. Running your amplifier direct from battery works by the sound of it. Audio signals are no match for may switch-mode converters which output anything from 10mV to 300mV of hash if not heavily filtered or fed into a low-drop-out linear regulator. Also many switch-mode chips will drop their frequency on low load directly into the audio band - a fixed frequency converter is least likely to cause issues, especially if it uses a very high switching rate (MHz).

    Of the converters you link I would hazard a quess the DROK one is quieter with its 800kHz switching frequency.

    Filtering probably needs an CLC or LCLC circuit for good rejection of noise, its probably much easier to go the linear regulator route, its standard for audio.

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