USB Charging

From The Neuros Technology Wiki

There was a discussion on the Neuros DM320 Hardware mailing list about USB charging. The results are summarized here:

• Benefits of USB charging (i.e. Why are we discussing this?)
  • One less connector, free space for something else
  • (possibly) No need for a separate DC adapter
  • Chargers for USB are widely available (Moto Razr, etc)
• Possible implementations of the USB charging
  • DC adapter combines with the USB host cable in a dongle
    • Pro: One port used on Neuros
    • Pro: Can supply all power required for a fast charge
    • Con: Difficult (but possible, expensive) to detect what combination of the DC dongle / USB host is attached
    • Con: Drawing too much power accidentally results in either a "Power Overdraw" message (bad PR, "My Neuros doesn't work on my computer"), or setting cheap non-power-regulating hubs on fire
    • Con: Still requires separate possibly rare-to-find DC adapter/dongle
  • DC adapter uses mini-USB but may not combine with a host
    • Pro: Easy to tell when to draw lots of current
    • Pro: Similar to the Moto Razr design
    • Con: Using the Moto Razr charger may fry the charger due to current consumption differences
    • Con: Cannot be connected to USB host while fast charging (lost versatility, confused user when Neuros Dock won't both connect to their computer and charge at once)
  • No DC adapter is used and device uses power from USB host only (single USB port)
    • Pro: Simpler, no DC adapter to lose, uses standardized cables
    • Pro: Many other devices do it this way
    • Con: Neuros fast charge requires more current than USB spec allows (slow charge only)
    • Con: There is no way to ask a USB host for more current than USB spec allows
    • Con: Drawing too much current outside of spec can cause USB host cutoff or smoky cheap hubs (see con of combiner dongle strategy above)
  • No DC adapter but we use multiple USB ports to aggregate the power
    • Pro: Will supply enough USB power
    • Con: Fast charge requires 3+ ports to remain in USB spec (annoying, ugly, many people don't have that many ports free)
    • Con: All of the ports would need to ask for full power - expensive to implement
• Alternatives
  • Keep DC adapter and USB ports separate, options:
    • Allow slow charge through USB host still
      • Pro: Versatile, convenient, charge your Neuros when on the run and you don't have the DC adapter
      • Con: Possible confusion, "My Neuros doesn't charge very fast" if they think USB and DC adapter are equivalent
    • No charging from USB
      • Pro: Consistent, always charges at the same rate
      • Con: No versatlity, lose DC adapter == dead Neuros
    • Manual selection of USB charging. ie. advanced users who know that their system or charger is capable of higher charging rates, can set their USB to "overdraw" current.