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Thread: DIY Teensy LC Eagle schematic (Welcoming Feedback)

  1. #1

    DIY Teensy LC Eagle schematic (Welcoming Feedback)

    Hello,
    I am requesting feedback regarding the schematic attached for a DIY Teensy LC in Eagle.
    I have omitted the 74LV1T125 and I will not be using USB power; an LDO will supply the +5V to VREGIN. I attempted to use the same parts others suggested elsewhere in this forum. I have not learned to create custom footprints yet so I use the Mouser ECAD libraries. Last note - I am using a usb-c connector.

    20220114.pdf

    Thanks!

  2. #2
    Senior Member propa's Avatar
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    Quote Originally Posted by mikemontauk View Post
    Hello,
    I am requesting feedback regarding the schematic attached for a DIY Teensy LC in Eagle.
    I have omitted the 74LV1T125 and I will not be using USB power; an LDO will supply the +5V to VREGIN. I attempted to use the same parts others suggested elsewhere in this forum. I have not learned to create custom footprints yet so I use the Mouser ECAD libraries. Last note - I am using a usb-c connector.

    20220114.pdf

    Thanks!
    Looks really good well done! I'm guessing that's a switch connected to the program pin? Maybe connect the other com to ground as well?

    Have you read anything about routing USB differential pairs? There's an easy tool in Eagle to make sure the paths have the same length and therefore same resistance, as they need to be matched (Route differential pair I think it's called). (Never routed differential USB signals myself just read about it, you may have come across it before, but just wanted to make sure)

  3. #3
    Quote Originally Posted by propa View Post
    Looks really good well done! I'm guessing that's a switch connected to the program pin? Maybe connect the other com to ground as well?

    Have you read anything about routing USB differential pairs? There's an easy tool in Eagle to make sure the paths have the same length and therefore same resistance, as they need to be matched (Route differential pair I think it's called). (Never routed differential USB signals myself just read about it, you may have come across it before, but just wanted to make sure)
    Thank you for your feedback! Yes, it is a switch (PTS810SJG250SMTRLFS) and I just realized the label for the switch is covering the MKL02 pinout. I fixed that. I also grounded the second COM pin.
    20220114a.pdf
    I didn't know the USB signals were a "differential pair" nor did I know they had to be routed with the same length but I have seen people use the Eagle tool to route with same trace length on youtube. I will have to check that out! I will post the board when I have it routed for more feedback. Thanks again!

  4. #4
    Senior Member propa's Avatar
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    Quote Originally Posted by mikemontauk View Post
    Thank you for your feedback! Yes, it is a switch (PTS810SJG250SMTRLFS) and I just realized the label for the switch is covering the MKL02 pinout. I fixed that. I also grounded the second COM pin.
    20220114a.pdf
    I didn't know the USB signals were a "differential pair" nor did I know they had to be routed with the same length but I have seen people use the Eagle tool to route with same trace length on youtube. I will have to check that out! I will post the board when I have it routed for more feedback. Thanks again!
    No worries, you're very welcome! And glad I mentioned the diff pair thing then, might have been an easy thing to catch you out on!

    I think it's do with any trace length has it's own resistance. You're doing something precise where you need exact same resistances on both lines like the USB pair. (idk how it works I'm assuming it's the same as balanced XLR in audio, where you use a positive and inverted/negative signal to cancel noise from the length of wire) Guessing if there's any difference between the pair it won't have the exact cancelling properties that's intended.

    Also don't take my word for it, I'm just assuming/guessing it's similar to audio xlr! this may help though: https://training.ti.com/layout-basics-for-usb-designs

  5. #5
    Quote Originally Posted by propa View Post
    No worries, you're very welcome! And glad I mentioned the diff pair thing then, might have been an easy thing to catch you out on!

    I think it's do with any trace length has it's own resistance. You're doing something precise where you need exact same resistances on both lines like the USB pair. (idk how it works I'm assuming it's the same as balanced XLR in audio, where you use a positive and inverted/negative signal to cancel noise from the length of wire) Guessing if there's any difference between the pair it won't have the exact cancelling properties that's intended.

    Also don't take my word for it, I'm just assuming/guessing it's similar to audio xlr! this may help though: https://training.ti.com/layout-basics-for-usb-designs
    Thank you I watched the TI Precision Labs - USB: Layout Basics for USB Designs on Youtube video and I will look into the topic further. It does appear that routing the USB according to differential trace impedance will require attention to trace length, width, spacing, ground planes, etc.. It appears for a typical 2-layer board the traces may be quite wide (approx. 30 mil trace width. with 6 mil spacing according to 1 example I found). More research to do.. Thank you for the tip!

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