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rotary_axis.f3z

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    • Forked from Jake Read / machineweek-2023
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    fab-step-log.md 2.31 KiB

    Log

    2020 11 05

    Started in, have the schematic mostly roughed out: this'll be 1.5 sided (solid GND below a routed layer). I think... the largest challenge is just getting things around themselves without using any vias. Found a tranciever as well.

    2020 11 16

    Just routed out the program / power / data interface side of this.

    routing

    Success going forward will rely on a a fortuitous alignment of the RS485 interface pins against a SERCOM port somewhere on 11-16... not at all sure if any such alignment exists.

    2020 11 17

    Lucky me, those line up. I can put the SERCOM's TXPO at 0 (for TX on SER-0) and and RXPO at 3 (for RX on SER-3) and the middle two will do data enable and rx enable, just GPIO.

    routing

    So, sorted that out. I think it works OK. I can make one of these in the fab-version, and can copy the schematic onto a smaller 2-layer board to fab lots of at a board house, having pins 17-20 free for an AS5047 on the back... same RS485 interface, maybe the QFN D21, and 0805s or smaller passives, pinch traces / spaces etc.

    2021 06 12

    Re-routed this for UCBus compatibility, still looks like the best option despite SPI availability: SPI interrupt handlers are minimum ~ 2us, meaning byte period of 2.6us (at 3MHz) is limiting, might as well use simplicity of UART, and ability / option for it to self-configure as P2P connection, etc. RS485 UART is same pin count as TTL SPI, would rather have noise / distance immunity.

    I left off some pins (SERCOM0) to potentially add an encoder here, the routing for that would be tough but probably possible.

    route schem

    2021 06 19

    Realized today that I had 5v, 24v lines on the plug optimistically configured for easier routing: the cable symmetry results in a more awkward routing which I've corrected, just had to squish the connector / RS485 bit up 1.5mm or so, so that I could wiggle those 5v and 24v lines beneath the connector:

    route schem

    2021 10 19

    Thinking about updating this w/ easier / simpler stepper hardware, have this list of new chips to try:

    • 296-DRV8434RGERCT-ND (stepper chip)
    • DRV8436RGERCT
    • 296-40076-1-ND (h-bridge w/ current sense output)
    • MAX14871EUE+CT-ND (A4950 a-la-moderne)