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Thread: Custom teensy for POV, stage: schematics

  1. #1
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    Custom teensy for POV, stage: schematics

    Hello, and happy new year for everyone,

    I'm finally making my POV-POI into PCB
    I use fritzing, as it is free and has no limit to board size.
    and thanks for PJRC community for all the references and related data.

    [Problems known]
    before I print some PCBs and go on, I need some help from below,

    1. I actually tried on some breadboards ,and I could't get a it working.
    with the MKL04Z32_TQFP32 bootloader chip connect, I get an unknown USB device recognized by windows(win10), beeping randomly, but teensy loader doesn't respond to program button, a teensy 3.1 would not beep that much and works fine. the jumpers were connected with jumpers as in schematics.
    with a total of 7, including ground and 3.3V.
    Still working on this. But not going to solder them myself again. maybe a few PCB manufacture tries is better?
    chips were from https://www.pjrc.com/store/ic_mkl02.html and soldered on TQFP breakout board with a momentary button.
    connect lines were with same pins mentioned in the chip page .
    Using a 40W solderer , not sure if chip damaged.
    I'll upload the pictures of the boards as soon as possible.

    2. Not sure if I should connect the crystall unused pins to ground or not.
    3. Voltage resistor questions as mentioned below.
    4. I may need power regulator choices.

    [Schematics]
    https://drive.google.com/file/d/0B30...ew?usp=sharing

    Sorry for dirty schematics, I left the schematics unarranged. and sorry about about the pin names, there wasn't a library for the MK20DX
    so I use atmege328 instead , as It gives the same TQFP64 layout, with some pins hidden in schematics.... should be fine if the pin numbers were correct.

    the LED driver part(TLC5947) were working fine under breadboard with teensy3.1.
    the power (TPS61200) was fine, or at least one of the tries was fine.

    there's also a switch, to power from the battery to TPS61200 . not shown in schematics yet.

    [POWERING]
    the power (TPS61200) schematics were same to, I give a few tries on breakout board with all needed parts and most of them failed.
    however, one of them worked and gives about 3.28Volts under USB power or Lithium battery (18650,3.7V)
    that's a good news, maybe my solder skills just can't confront QFN10 package.

    Also considering for a really Low LDO regulator like HT7333.

    but not sure if the current supply will be enough, or not
    http://www.digchip.com/datasheets/pa...196/HT7333.php

    the 3.3V power line was used for SD/MK20DX256 /,but not for lighting the LEDs(they were driven directly by battery power, and they works normally)

    btw, I'm not sure, but MK20DX256 seems to give 1.1V internal analog reference, according to my testing value.
    A voltage regulated to 3.3V would be fine to be the DEFAULT reference, or I need a bigger divider.

    [Finally the main function]
    Read .bmp from SD, store the whole picture to SRAM, then draw the pictures with TLC5947,
    using software SPI. Could bit-bang a 36pixel/RGB up to 1000lines a second.

    A0(p58) and A12(p11) to get volt reading from battery, and USB , while charging.
    I tried 1.2M divider with teensy 3.1 and get incorrect results, so I lower the resistor values to 10K ohm.
    Anyone have a better idea on this? A battery device should be when unpowered, 10K*2 seems to get a 200uA(under 4Volts) leakage and still acceptable.

    -----------
    thanks for everyone reading the topic, Happy new year!!!!!!!!!!!!


    [References]
    http://www.appfruits.com/2015/03/bui...custom-teensy/
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Po Ting; 12-31-2015 at 10:31 PM.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    I'm sorry, I can't help based on this schematic. In general, I can't provide much support for custom PCBs. Sometimes I take a "quick look". I don't want to be too negative, but this schematic is a mess. You really need to use the proper chip with pin names correctly assigned, if you want me or anyone else to read it. Using the wrong chip may allow you to use the schematic to create a PCB layout, but it just is not good enough for the purpose of communicating with other people about your design.

    Regarding the design, are you building this first as a prototype with a working Teensy 3.2 board? Issues like the resistor values and circuit design should be designed and tested on a prototype BEFORE you attempt a custom PCB.

  3. #3
    Senior Member Constantin's Avatar
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    I tried to read your schematic on google drive. That's going to need some cleanup before I attempt to go further, it's way to confusing. Chances are, you missed a connection and can't see it for the forest of lines bisecting each other.

    Eagle can be particularly naughty in this respect as you can sometimes draw connections to component pins in schematic view but the connection is not actually made... Thus, after making all connections to a components pins, I will always move it around to see if all the 'connected' lines actually follow the component pins around on the schematic. If you look for lost connections in BRD view, you'll likely lose that battle in anything but moderately busy boards.

    My suggestion is as follows: start your schematics over and emulate a known-good schematic like the one from Paul. That makes it much easier to see where issues may be. I have posted Eagle libraries for Teensy components that mimic Pauls schematic in most ways.

  4. #4
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    thanks Paul,
    I'm Sorry for the schematics
    here's a new version with pin names relabeled , and I'm working on cleaning other parts' schematic.
    https://drive.google.com/file/d/0B30...ew?usp=sharing

    I know not much about arduino,teensy, C code and what ever related before September.
    Every time I moved further that's a lot of fun, I appreciate any help and I would be glad to follow the rules of designing schematics, codes, etc.
    Maybe I should start leaning EAGLE?

    from the datasheet of MK20DX256 , it says the resistor value from the voltage to ADC pin must be as low(<5K?) as possible to get best results.
    I've tried a few values for the resistor value for the voltage dividers for the ADC pins, 1K seems to be accurate, but there's leakage problem since i use batteries,
    1.2M would get an inaccurate analogRead(); value. 10K was my current design, and worked with a about -5~10% error.
    I don't have all the values of resistor on hand (should buy a changeable resistor...) so I'd like to know if anyone tried other value, and if they were accurate?

    and not sure if the board could be called prototype
    I'm pretty sure SD part and LED driver part work with a teensy, power may need adjustment. and also some coding problem.
    the question lies mainly on coding the chip with bootloader, and it's where I found it not working.

  5. #5
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    Here's reconstructed power and LED driver schematic.
    they basically would work as I construct the schematic first-> mess it up while building PCB ,
    and clear up again to share with the community, they were drawed in Fritzing

    the naked TLC5947
    https://drive.google.com/file/d/0B30...ew?usp=sharing

    the TLC5947 schematics were modified from https://learn.adafruit.com/tlc5947-t...bly-and-wiring
    and with a pullup on blank line, so the LEDs won't flash before teensy start giving signals.
    my customed TLC5947 PCB worked fine and tested with the adafruit TLC5947 library&example.
    ------
    if you want to use the schem, take care
    the schematic was naked, with no LEDs connected, the order of RGB LEDs must be dealt carefully on software and hardware.
    ------

    while the POWER device TPS61200 only had one of the several tries worked and gives 3.3V correctly , guess the problem is my soldering skill

    TPS61200
    https://drive.google.com/file/d/0B30...ew?usp=sharing

    my devices are somehow separable so I can complete the parts one by one, and modify only one of them if needed.
    Last edited by Po Ting; 01-06-2016 at 10:59 PM. Reason: naked

  6. #6
    Maybe I should start leaning EAGLE?
    Yes, please learn Eagle. I also started with Fritzing when it first came out publicly. Fritzing so limited and if you do not get away from it now, it will be harder to learn a proper Cad program. There are tons of tutorials for Eagle and it's free with some minor limitations.

  7. #7
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    @Ross
    actually, a limit to size drives me away from EAGLE on November
    unfortunately my board is designed to a thin but long 2x25cm

    I remember Fritzing is the first I found with no limiting board size
    the different white background and less buttons was probably the other reasons
    though encountering crashing and missing parts
    I can still expect their new version with better features( more board layers, part editors, whatever)

    but sure, I shall have some tries on other possibility, I have much more sense in PCB than I had a few months ago,

  8. #8
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    You could try out Kicad, its not the greatest but its free and it does do a good amount. I use Free Eagle, Kicad and at one point GEDA.

  9. #9
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    time have passed and just to tell I did suceed created some nice POV-poi/staff

    at 2016 , prototype were with lots of failure, mostly on PCB assembles, though some of the batch did worked.
    I went on giving up using the MK20 chip, but use a whole teensy 3.2 instead.
    so I don't need so much parts and mess up
    and also, with 3.7V(lithium) coonnect to teensy's Onboard Vreg(Vin),
    the voltage was still enough to work though battery's power cycle.

    after T3.6, with hardware SDIO the project is even achieved with high density/more pixels.
    with SDIO, DMAspi (to LED/apa102), overclocking, the refresh speed of POV went overkilling,
    hopefully can support to 200 pixel or more in future versions.

    I'm looking back to what I've prototyped, examining
    failed on PCBA, hand soldering / some failed by small-batch solder retailers.(so one should find PCBA with trusted skill)
    I think the parts were not likely to fail, even if they were recycled, or counterfeits if I could tell.
    maybe its the high humidity here cause some unknown problem with hand solder?
    with TQFP(MK20) sometimes I can see spark jump between pins, but no solder/short seen in sight
    must have invisible residue traces that gives weak connection and drives the chip crazy.

    and with T3.6 made with BGA chip, so hard to solder or prototype
    I think I'll keep the Teensy intact for all further versions.

    okay, enjoy some POV pics~
    these are photoed with 72 pixels POV
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    Last edited by Po Ting; 09-17-2017 at 11:12 PM. Reason: realign attachments

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