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Thread: Minimal circuit for USB host with Teensy 4

  1. #1
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    Minimal circuit for USB host with Teensy 4

    Hi,

    I've skimmed through a few of the breakoutboard threads and am fascinated by the technique to get to the pads on the bottom, but a little overwhelmed at this point. I'm comfortable with Ethernet/OSC, older and newer W5500 boards with the pjrc SD daughterboard, midi/sysex and whatnot. I'd like to do a simple headless 2-way OSC-midi bridge to use with older Behringer BCF or the newer X-Touch controllers and their X32/X-Air mixers. The controllers are self powered and i'm wondering what extra components i need to safely connect to a Teensy 4? Or can i just solder VIN, D-, D+ and GND to a USB-B panelmoiunt breakout and get on with it?

    thanks,

    Carlos
    Last edited by chaosmoon; 11-30-2019 at 11:39 PM.

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    Quote Originally Posted by chaosmoon View Post
    Hi,
    The controllers are self powered and i'm wondering what extra components i need to safely connect to a Teensy 4? Or can i just solder VIN, D-, D+ and GND to a USB-B panelmoiunt breakout and get on with it?
    The extra circuitry in the Teensy 3.6 (copied into the Teensy 4 USB Host Breakout) provides power overload protection, power control, and USB ESD protection.

    If you are willing to bet that you won't need this protection, then go for it!

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    Quote Originally Posted by blackketter View Post
    The extra circuitry in the Teensy 3.6 (copied into the Teensy 4 USB Host Breakout) provides power overload protection, power control, and USB ESD protection.

    If you are willing to bet that you won't need this protection, then go for it!
    Ah yes the 3.6 Thanks for pointing that out. I wasn't aware of the fact that it has all the USB circuitry on board! I'll find other uses for the 4 boards and go with a 3.6 for this one. There's enough pins on that for all sorts of other stuff too. (so much for headless)

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    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by chaosmoon View Post
    Or can i just solder VIN, D-, D+ and GND to a USB-B panelmoiunt breakout and get on with it?
    Usually you can get away with omitting the current limit chip and big capacitor if...

    1: Your USB device uses only a moderate amount of power, relative to whatever is powering Teensy. Mainly this can be an issue if Teensy gets its power from a USB cable, which must then power Teensy plus the other USB device.

    2: You avoid hot-plugging, so the device is connected when you power up and you don't unplug and reconnect while the power is still on.

    Consider that most of the USB host shields made for Arduino boards use only 10 uF and only a PTC "fuse" rather than graceful current limiting chips. They generally work because they have a dedicated voltage regulator to create a strong 5V supply, but only when the Arduino board is powered by a power adaptor. With only 5V from USB to power the Arduino plus one of those shields, they work about the same as if you just connect the 4 wires of a USB cable directly to Teensy 4.0.

    Unlike those host shields, which are 12 Mbit (and limited by SPI speed & overhead), the USB host port on Teensy 4.0 and 3.6 is 480 Mbit speed. Use a proper USB cable and keep the length of wires broken out the cable short, like under 1 inch or ~2.5 cm. Keep the white and green signal wires and a ground wire as close to each other as reasonably possible.

    If you power Teensy from an external power supply that could deliver more than 1 amp, a PTC or normal fuse (or current limit chip) is supposed to be used, so a short in the device or connector won't sustain a high current which could melt or burn the USB cable. The world is filled with cheaply made cables. Don't risk starting a fire if you have a powerful 5V supply.

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    Quote Originally Posted by PaulStoffregen View Post
    Your USB device uses only a moderate amount of power, relative to whatever is powering Teensy. Mainly this can be an issue if Teensy gets its power from a USB cable, which must then power Teensy plus the other USB device.
    My initial idea is for use with self powered devices.

    Quote Originally Posted by PaulStoffregen View Post

    Unlike those host shields, which are 12 Mbit (and limited by SPI speed & overhead), the USB host port on Teensy 4.0 and 3.6 is 480 Mbit speed. Use a proper USB cable and keep the length of wires broken out the cable short, like under 1 inch or ~2.5 cm. Keep the white and green signal wires and a ground wire as close to each other as reasonably possible.
    Is the cable length still so sensitive with the correct circuitry on the 3.6 and 4.0 breakout boards?

    Quote Originally Posted by PaulStoffregen View Post
    If you power Teensy from an external power supply that could deliver more than 1 amp, a PTC or normal fuse (or current limit chip) is supposed to be used, so a short in the device or connector won't sustain a high current which could melt or burn the USB cable. The world is filled with cheaply made cables. Don't risk starting a fire if you have a powerful 5V supply.
    I had a look at the 3.6 schematic and managed to identify the TPD3S014 chip. Are there any through-hole solutions or better yet USB-only breakouts? Otherwise i'll look into the breakouts like Blackketter's but the double pin rows means that i'd probably end up making boards for the breakout. Veroboards without lanes just get me confused.

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    Senior Member+ MichaelMeissner's Avatar
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    It is a shame that the loglow/talldog board hasn't progressed to retail sales at this point:


    On some prototype boards, the rows of connected pins are broken up so that you could have the USB pins in separate set of rows.


    The third possibility is use male headers on the normal pins that connect to the normal pins and are brought out normally. And have female headers on the USB bits that don't connect to the prototype board underneath.

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