Isolating X2 logic power

We’re running the X2’s on our robot off of a 6V battery. Because voltage can drop under load, we want to try to isolate the logic power to avoid brownouts, possibly using a separate battery for the logic. We’ve identified 3 possible approaches… can you comment on if any is better than the others?

  1. Wiring in regulated 5V power to the power/ground pins on the I/O block, as some have done before, and removing the power switch to avoid powering the onboard vreg. Pro: Easy to do. Con: Removes an I/O port. Somewhat easy to dislodge. Questionables: Will this damage the vreg? Are the traces able to handle the distribution (assuming we don’t do any high current tasks like running servos).

  2. Wiring in regulated 5V power to the USB port, shorting the USB-VCC jumper on the bottom board, and removing the power switch as above. Pro: Harder to dislodge (we work with kids, so it’s nice to have), preserves the I/O port. Questionable: The USB-VCC trace is smaller; can it handle 500mA?

  3. Clip the pins connecting VBat from the motor driver board to the bottom board, then wiring a separate connector using the V+/- holes at the top of the bottom board. Pro: Don’t need to regulate incoming power. Con: Hard to reverse. Questionable: Do those power pins serve other purposes?


I think option 3 is the best. I think your con there is not too bad since you can always just put in a wire to reconnect VBat. By the way, even a very small trace (8-mil) can carry 500 mA, so if that’s your maximum current, you generally don’t have to worry about the trace thickness when looking at your options.

- Jan