• First failures

    Anton Gerasimov08/03/2020 at 19:26 0 comments

    The board conceptually has three parts:

    1. Power converter driven by LMZ2701
    2. UART level shifting with TXS0102
    3. USB<->Serial interface (FT230X)

    Out of these three parts two had fatal flaws in the first (aka v0.8) revision.

    The power converter was the one that worked well - mostly because it was copied verbatim from the datasheet.

    Level shifting failed because I haven't noticed that the two ports of TXS0102 are not symmetric: namely port A is for the lower voltage part (3.3V in this design), and port B is for the higher voltage (5V). Of course in the first revision they were connected the other way round.

    FTDI failed because wrong TX/RX connection (who would have thought!): it was connected to talk to Raspberry Pi instead of Roomba. In addition a bypass capacitor was missing in one place, which didn't show an immediate effect on the performance though.

    On the bright side, it was my first successful experience with reflow soldering, and the mistakes were quite obvious, and easy to fix which was done in the next revision. In addition the first revision (the power was working well as you remember) confirmed that Roomba can provide enough power to drive a connected Raspberry Pi Zero W streaming data from the camera.