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  1. #31

    Re: Malum IK

    I have used exactly this circuit to interface between Teensy 3.2 and 3.5 and the DXL bus, yes!

    The RX pin has a 560 Ohm / 1 kOhm resistive divider to translate the 5V of the buffer chip down to the 3.3V accepted by the Teensy.

    Note: The TX pin doesn't have a pulldown here, but the direction does, so in practice, it doesn't matter. The main change I've done since this diagram is increase the R304 value to 10k to draw slightly less current (the time to switch doesn't change perceptibly) and add a 100k pulldown on the microcontroller TX pin, because by general practice, no pin should be undefined on startup.

    Btw, I have a story to tell about this latest board version, and how I had to iterate several times through Macrofab to get it right (at no cost to me! They've been very good about that.) It started with them placing an IC 180 degrees rotated, which caused other failures, which caused rework, which caused other failures of things that previously worked, ... This was exacerbated by not being able to inspect the soldering at the bottom of those QFN packages. In the end we made a new board, using SOIC/TQFP style packages, and that worked fine! From this experiene, I conclude that QFN ("quad flat no lead") is as tricky as BGA to get right.
    But, that has taken a lot of time to get over the finish line. When I finally got a working board on the fourth(?) iteration, I was kind-of low on gas, and it's sitting without a chassis to screw it in to, because of course I need to re-cut the chassis to fit the new board, even though it eventualy ends up integrating more functions and requires fewer external little drivers/boards.

    Also, the AD opamp based video switch seems to work great, although I can't genlock the two cameras to each other, so there is some time to re-sync when I switch.
    Last edited by jwatte; 12-01-2019 at 01:05 PM.

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