JohnSwenson wrote: > It sounds like you are talking about a USB jack that is JUST for power, > not a real USB that connects to a computer to send data over correct? > Will this confuse people? Will they try and hook it up to a computer and > expect to use it as a USB DAC? > > I have been looking at the possibility of bringing the OTG port on the > module out to a micro jack on the, will it be confusing if we have one > of these and another that looks the same, but is the power jack? That > bring up the next question, do you want to power the box off the OTG > USB connection? I'm not sure you can get enough current off a USB host > port, and even if you can, there is the sequencing requirements. > According to the USB spec if you are going to draw a lot of current, > when you first connect you have to draw a small amount, then negotiate > with the host for the larger amount, only when the host says it's all > right are you allowed to take the large amount of current. Unfortunately > there is no way the wandboard module is going to be able to run off > the initial small current, so there will have to be a separate circuit > that talks to the USB, just for the purpose of negotiating the current. > I really don't want to go there. > > The "charger" spec is different it allows a device to pull the larger > current without first doing the negatiations, but not all ports on > computers are "charger" ports. There are data ports, data ports that can > be charger ports as well, and dedicated charger ports. The ones on > actual USB chargers are obviously the charger only type. Some ports on > computers are dual mode and some are only data. On some laptops you can > have some ports supporting charging and some not. It can get a little > confusing when it works on one port but not another of the same laptop! > > > So what I think I'm getting at is that If I decide to go with the OTG > port so the box can be used as a USB DAC, I do not want it being > powered off that connection, it's just too much of a hassle to do so. A > seperate "power only" jack is doable, but it should be used with a USB > charger. Trying to draw the power from a computer may or may not work > depending on the type of port it is connected to. > > John S.
For what it's worth, I think you're spot on with the assessment of using a USB connector for power-in. Unless you can conform to all USB2/3 port behaviors, in terms of powering up and then negotiating for extra power, do not use a generic USB connection for power. A barrel connector is the best for a lot of reasons, not the least of which is that it is the most common connector on DC inputs for non-portable consumer electronics. You can easily get replacement power supplies that provide the same spec for the power. And I do think it would be confusing if you had two USB connectors on the device. Much better to have a USB/barrel connector, in my opinion. -=> Jim ------------------------------------------------------------------------ JimC's Profile: http://forums.slimdevices.com/member.php?userid=9428 View this thread: http://forums.slimdevices.com/showthread.php?t=97881 _______________________________________________ discuss mailing list discuss@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/discuss
