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Thread: Teensy 4.x custom board possible?

  1. #1
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    Teensy 4.x custom board possible?

    Hello I would like to create a teensy 4.x custom board. You might ask why i chose teensy, is primarily because is fast and because most importantly can be programmed by the Arduino IDE which makes me not have to rewrite libraries for my modules.

    My Questions are.

    1.) If buy all the IC in the teensy 4.x schematics and smack them into a pcb would they work instantly? No bootloaders to install ? I willing to buy the boards and desolder the parts anyway . Buying the IC individually would save me some time and a few dollars.

    2.) Im primarily looking at teensy 4.1 because of the number of pins it have, Does it still have I/O pins i can use (using Arduino APIs) that were not eposed in that board?

    Thank you very much.
    Last edited by JakeQuinn; 05-23-2020 at 02:53 PM.

  2. #2
    Senior Member+ KurtE's Avatar
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    Obviously @Paul can answer this a lot better than I can.

    I don't believe the bootloader chip is available yet for T4.x - I believe he made progress on that during T4.1 beta time. Put with their current quarantine rules, it is only Paul and Robin, so it might still be awhile.

    T4.1 and other pins - Yes there are more pins on the processor than were exposed. Could others be exposed? Probably. As for using them as Arduino pins, you mainly need to add them to all of the underlying tables and the like. As example of how to do so. Simply search the core files for ARDUINO_TEENSY41 and you will see how he ones for T4.1 were added to extend on on the T4 pins were defined. But with all of these things there are some things you will find out by Trial and Error, or being really good at extracting the data from the reference PDF.

  3. #3
    Quote Originally Posted by JakeQuinn View Post
    1.) If buy all the IC in the teensy 4.x schematics and smack them into a pcb would they work instantly? No bootloaders to install ? I willing to buy the boards and desolder the parts anyway . Buying the IC individually would save me some time and a few dollars.
    No. There is a bootloader on a separate chip which will be available to purchase at some point, but is not yet.

    Quote Originally Posted by JakeQuinn View Post
    2.) Im primarily looking at teensy 4.1 because of the number of pins it have, Does it still have I/O pins i can use (using Arduino APIs) that were not eposed in that board?
    Yes, but there are much easier ways to add more I/O to the Teensy depending on your requirements.

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    Well thats unfortunate. But its alright ill ust have to desolder the chips then, i assume that the schematics of the teensy 4.1 in here is all of it, no hidden stuff. As for the extra pins i think i will just have to come back with another forum question when i get to sort out this project of mine a lot better.

    Thank you good sir, hopefully maybe by that time the bootloader will be available.

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    I try to first avoid port expansion when there is onboard pins, but if its that hard to implement them i might go that route

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    If you're making many of these devices, and you only need programmability for development, then you can use another programmer (such as a JTAG programmer) to program the production chips once you have a sketch you are satisfied with. In that situation, you will develop using a Teensy with the small programming MCU connected, but the production unit will not have that programmer chip, and instead you'd connect to it once with a JTAG programmer and load the Teensyduino-compiled binary into flash.

    Personally, I just put female headers on the PCB, plugin a real Teensy for each copy, and live with the additional height this takes up (about 1/4" above the tallest other component I have, which is a connector.) It's much less fuss, and if I happen to destroy the Teensy, replacement is super simple. But I don't make that many copies of my boards.

  7. #7
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    This is the Teensy 3 bootloader, so not what you want to buy
    https://www.pjrc.com/store/ic_mkl02.html
    But the links down the bottom includes a bunch of threads on other people's ventures that would be applicable.
    Unscientific analysis indicates that getting the crystal design right is tricky, with some others having trouble getting the all the pins involved in the reset/bootload sequence to the right places - There are multiple ways to program the raw uC and some of the 'spare' pins may have been left unconnected by design to make sure bootloader is the only thing trying to program the chip - see adventures with pin 33 in the early days of T3.x series.

  8. #8
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by JakeQuinn View Post
    Well thats unfortunate.
    A bootloader chip is coming. Details here:

    https://forum.pjrc.com/threads/57132...l=1#post221811

    As Kurt explained, we're short staffed here due to Oregon's covid19 shelter in place order. That's putting serious limits on how much development (or even just answering questions) I can manage to do while we struggle to just run the business.

    At this moment, my highest priority is updating the website. Many pages that mention Teensy 3.x still need updates for Teensy 4.0 & 4.1. Some very old pages are still only about Teensy 2.0 (and probably won't get updated anytime soon). Today I've been working on the audio design tool documentation (and *not* working on the bootloader for DIY use).


    But its alright ill ust have to desolder the chips then,
    If you do this, make sure you use the same IMXRT1062 and MKL02 and W25Q64 together. How to re-solder a used BGA chip is something I don't know, but I've been told a special machine is need to "re-ball" the BGA.

    When we do sell MKL02 chips for Teensy 4, those chips will auto-detect which flash chip you connected, and they will detect when a virgin IMXRT chip is used and properly initialize the fuses. Those features are partially present in the MKL02 chip on Teensy 4.1 (and completely absent on Teensy 4.0), but still not fully tested for making a DIY board that isn't initialized by a custom test fixture. Your DIY board very likely will not work if you substitute a virgin IMXRT chip for the one you desoldered from Teensy 4.1, using the desoldered MKL02 chip.

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    I will most probably be making one to three, plugging a teensy would kinda beet one of the reasons im making this board thus the extra steps

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    Thank you for having the time to reply to my thread

    Thanks for the update, looks like the feasible approach to my project right now is desoldering chips on a teensy board.

    If you do this, make sure you use the same IMXRT1062 and MKL02 and W25Q64 together. How to re-solder a used BGA chip is something I don't know, but I've been told a special machine is need to "re-ball" the BGA.
    No worries though i am fairly confident i can reball BGA just fine, using the stencil that will come with by board.

    Your DIY board very likely will not work if you substitute a virgin IMXRT chip for the one you desoldered from Teensy 4.1, using the desoldered MKL02 chip.
    So as long as i stick with the chips on a single board ill be fine.


    May i ask, if ever im going to use the teensy 4.1 are the unused digital pins safe to use? incase i need more GPIO i only need them as digital pins.

  11. #11
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by JakeQuinn View Post
    May i ask, if ever im going to use the teensy 4.1 are the unused digital pins safe to use? incase i need more GPIO i only need them as digital pins.
    Generally speaking, it's fine to use the other pins, as long as you add the necessary software to do so. But I hope you can understand my reluctance to specifically recommend changes we haven't tried or tested. This chip is filled with a lot of very powerful features, which sometimes are quite complicated to use. I hope the Teensy 4.1 design can help you get going, but design changes that you make from what we use on Teensy 4.0 & 4.1 are ultimately your responsibility.


    Quote Originally Posted by JakeQuinn View Post
    ... plugging a teensy would kinda beet one of the reasons im making this board thus the extra steps
    I'm curious what you're up to? Can you tell us what those reasons are, that you can't just use Teensy in a socket?

  12. #12
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    Quote Originally Posted by PaulStoffregen View Post
    But I hope you can understand my reluctance to specifically recommend changes we haven't tried or tested. This chip is filled with a lot of very powerful features, which sometimes are quite complicated to use. I hope the Teensy 4.1 design can help you get going, but design changes that you make from what we use on Teensy 4.0 & 4.1 are ultimately your responsibility.
    Thank you for the heads up, since i have no idea whats going on with the bootloader maybe its used for some other function, thats why im a bit hesistant.

    Quote Originally Posted by PaulStoffregen View Post
    I'm curious what you're up to? Can you tell us what those reasons are, that you can't just use Teensy in a socket?
    Im still a student at a university, and in one of my subject we are being taught to make PCBs as a transistion from perfboard and breadboards. Sockets components are not allowed as that would mean your pcb is acting like a breadboard or a perfboard (not getting to deep the reason why, lets just say that a must requirement). And you might say isnt BGA a little bit too hard for a beginner? I have a reputation from fixing electronics part time, so yeah i have to live to the expectation . As for what i plan to make, right now is a multi motor controller along with other sensor board for a another class project i have. hitting two birds with one stone

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