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Thread: Advice regarding circuit design and the bootloader

  1. #1
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    Advice regarding circuit design and the bootloader

    I am the first to confess.... I am new to designing my own circuits.

    But, I have a project that I am moving over from my Teensy 3.2 breadboard to a PCB design.

    The Teensy 3.2 circuit diagram here has no bootloader? (Why is the diagram missing a vital part of its actual design)?

    https://www.pjrc.com/teensy/schematic.html

    I have designed my PCB using the circuit diagram above, but now realise that I have no way of loading to it.

    Advice please!

  2. #2
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    Or I could be talking complete rubbish.... is U2 the bootloader?

    I assume USB0_DM is USB negative and USB0_DP is USB positive?

    There looks like 3 IC's on the Teensy 3.2 board. Damn my 53 year old eyes.... where is my microscope

  3. #3
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    Yes, u2 is the bootloader.

  4. #4
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    After extensive Googling.... I sussed that out. Thanks

  5. #5
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    So, my first attempt at a PCB is assembled. And when you plug it into the PC, it does not recognise it (no windows acknowledge sound).

    Can't see any wiring/design error (yet). Should a bare new IC as the Teensy wiring diagram be detected immediately? Or am I missing something.

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    Right, pretty obvious really. I need to load the bootloader software to the bootloader! But, that isn't available is it.
    So... my project dies right there.

  7. #7
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    Quote Originally Posted by SteveSFX View Post
    Right, pretty obvious really. I need to load the bootloader software to the bootloader! But, that isn't available is it.
    So... my project dies right there.
    No, you can buy it from PJRC.

  8. #8
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    ... or just solder the 3.2 to your PCB. If it is your first PCB, this would be the better way, anyway.

  9. #9
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    Yes, I found the link to the pre-loaded bootloader. Expensive however (but I totally understand why).
    Made hundreds of stripboard and breadboard projects. Time I learnt pcb construction.

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    Hmm.... Nearly $20 and a 2/3 week wait (post to the UK) for a single pre-programmed MKL02Z32VFG4

    So, I either buy a Teensy 3.2 off UK Amazon for 20.89 and lift the bootloader off that (which also gives me a pile of other spares including a processor), or totally re-design the board using something else.

    Leaning towards the second option... Time to Google

  11. #11
    Senior Member BriComp's Avatar
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    18 from Pimoroni, admittedly with 2.99 p&p.

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    I went with the TEENSY 3.2 for several reasons. 5v tolerant (although, I could design in level shifters), and it's ability to be HID device. Oh, plus I had one.

    I originally started with an STM32, but for the life of me, cannot remember why I stopped mid-project and changed to the Teensy. Must have been some reason.

    But, I need to head back away from the Teensy I think. It's too expensive for my requirements.

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    Hello chaps

    I have several Teensy 3.2's dotted around in finished projects. If I 'lift' the bootloader IC off one of those boards, will the board still run?
    I Googled bootloaders and there seems to be split opinions on whether the bootloader is only needed for new programming, or needed at every single boot.

    A 3.2 runs the access control to my workshop, so that will not ever be getting 'edited' again.

    Lost my job back in Feb and the future is looking bleak.... 20 is a lot at the moment!

  14. #14
    Senior Member PaulStoffregen's Avatar
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    A previously programmed Teensy 3.2 should continue to run its previously programmed code if you remove the MKL02 chip, assuming you don't damage other parts of the Teensy 3.2 during the desoldering process.

    I too am frustrated by the high postal international shipping costs changed in by the USPS. Here's a mini rant I wrote recently.

    https://forum.pjrc.com/threads/64717...l=1#post260974

    But sadly, the end result is we really can't do much about the shipping cost. If you go to the USPS website, you can see the high prices they charge!

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    Thanks you Paul. This isn't me 'dodging' buying the correct parts I should add. I fully intend to carry on using Teensy's in my projects when (if) my income resumes.

    I designed a pcb a while back (my first ever) and had it made, totally without thinking really. That uses the processor and the bootloader. No idea why I didn't twig that I needed a programmed bootloader. So the board is sitting there unable to be finished.

    Pretty sure I can lift it off carefully with my SMD heat gun and the mini nozzle I made for it. The project I intend to remove it from has a standard 3.2 in it, so if I mess it up, at least I can simply plug a new programmed 3.2 into the breadboard IC holder.

    In future, I'll know that I need pre-programmed bootloader ICs.

    As a side note, I split my last smd components order between RS in the UK and Digikey in the US. Digikey was FAR superior. I am UK based.
    The parts were mostly cheaper and available in smaller quantities from Digikey (not everyone needs a minimum order of 20 bespoke slideswitches Mr RS), and turned up in one package, and within 3 days. No parts missing and just over 34 in total.

    RS on the other hand... Order arrived literally individual item by item, spread over 2 weeks. Some days, a jiffy bag arrived with one pack of 25 0805 resistors in it. I think in total, I had 16 packages for a 35 order. None of the parts said they were outside the UK when ordered, but it turned out that several did end up coming from the US.

    Then some items turned up twice. Total mess.
    Not to mention that even though I paid the full sum at checkout, they took the individual amounts out of my bank account as they posted them. I had an entire page on my bank statement dedicated to a 35 RS order.
    Will never use them again.


    Thank you for the advice Paul
    Last edited by SteveSFX; 12-02-2020 at 08:46 AM.

  16. #16
    Senior Member PaulStoffregen's Avatar
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    This sort of desoldering is risky. It certainly can be done with good tools and skills. However, it is easy to damage the PCB if things don't go perfectly.

    If you're not in a financial position to afford a $20 "learning experience", perhaps the wise path would be to just leave well enough alone for now?

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    Yea I know. But GOD I'M BORED. Just tinkering around with projects to fill the days at the moment.
    Trouble is, you say... 'I'll just buy that bit for $20'... and it never ends

    As a side question. What kind of temps do people use with their desoldering air guns? I run mine at about 350 on the lowest speed. Seems OK, but I can't seem to ever 'harvest' spare parts off old commercial PCB's even with the heat wound up to 500. It just never seems to release them.
    That I assume is either down to heat dissipation through the much larger PCB's, or higher temp solder? I wanted to salvage some SMD elect caps the other day and just could not get them off the board.

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    I think in hindsight Paul, I will wait and order a handful of bootloaders from you. Will probably throw in some extra Teensy 3.2 modules as well.

    Just wish this Goddam world would get back to some kind of normal, but that is a way off yet. Unfortunately, my career is dead in the water (SFX engineer for stage and live events). Nothing on the horizon at all

  19. #19
    Senior Member fdaniels's Avatar
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    For desoldering Components: maybe add a touch of leaded solder. Helps with THT any time.

  20. #20
    Senior Member BriComp's Avatar
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    Quote Originally Posted by SteveSFX View Post
    Hello chaps

    I have several Teensy 3.2's dotted around in finished projects. If I 'lift' the bootloader IC off one of those boards, will the board still run?
    I Googled bootloaders and there seems to be split opinions on whether the bootloader is only needed for new programming, or needed at every single boot.

    A 3.2 runs the access control to my workshop, so that will not ever be getting 'edited' again.

    Lost my job back in Feb and the future is looking bleak.... 20 is a lot at the moment!
    You could use MyUs.com to ship to the UK. They will set up a US address for you. Have stuff sent there and they will forward it to the UK.
    I have just set up a MyUS.com account for myself. The basic account is FREE.
    I ordered a HK Hynix NVME 1Tb drive for $121.78. Shipping to the UK will be $10.99. If I have to pay VAT (Get Caught) that will cost me 135, 105 without. The UK price from Amazon is 212.
    If you used this system for a bootloader it would cost $6.95 + $3.85 + $10.99 = 17.16. In this case it would be cheaper to buy from Paul as his total cost would be 14.88.

  21. #21
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    Have you thought of supplying the stand-alone bootloader IC's through the UK suppliers of the Teensy main boards Paul?

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