I own some inexpensive yi home cameras. I don't like having a cable run to a wall wart for each camera. Is it possible to run low voltage wires in the walls to a central 5v power supply with sufficient wattage, and splice to the VCC and GND wires in USB cables? Or does power over USB require communication?
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1\$\begingroup\$ Rather than the communication matter, what worries me is that running 5V (with possibly quite some current, especially if you share some cable portions with multiple cameras: I don't know how much power the camera uses, some ads indicate 3W, so ~600mA) through the wall, where the cable length can be significant, may result in a voltage drop which may exceed the USB tolerance on VBUS. In this case, the cameras may not work. Use thick wire to mitigate this. \$\endgroup\$– dimCommented Feb 9, 2018 at 21:00
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3 Answers
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Many require smart controllers for battery chargers, but not cams or mobo/mobile part.
I prefer a dumb 6 port USB hub with 2.4A per port. (60W max) cheap. So some peripherals need smart data for charger part but not to operate from external power.
There is a wide range of options or you can route suitable phone wires from your 5V ATX supply with a polyfuse to each plug.
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According to the USB standard, more than a certain amount of power over USB does require communication, but in practice it may not be necessary. Battery-powered devices like phones will often draw a maximum of 500mA from a USB port by default, but will require some kind of “communication” to draw more than that. Often a very simple form of communication will suffice, such as Apple’s voltage divider scheme.
Devices that don’t charge an internal battery can’t easily vary the amount of current they draw. These devices will often not use any form of communication, especially if there is no host present, and will simply draw as much current as they need. I have a Yi camera myself and once took it apart, and would guess this is the case for these cameras. So what you are planning will likely work.
Beware that very long cables will dissipate power in the cable and cause a voltage drop at the device end. Depending on your particular device, this could cause problems including random resets.
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Power over VBUS doesn't require any USB communication with USB protocol.
However, optimal power for your cameras might require proper "charger signature" on D+/D- wires to inform your device about source power capability (which is a sort of communication too). You should do some research on the charger/adapter that is supplied with your YI cameras, and provide the same D+/D- hook-up on your split cable harness. Your camera needs 5 V at 1 A DC power, so the signature is likely simple, a DC-type. If no resistors are connected or D+ is not shorted with D-, then the split cable is good to go as it is, VBUS and Ground. I would guess that Chinese charger signature (D+ shorted with D-) is most likely, so you should connect green-white pairs in your cables, preferably individually.
answered Feb 9, 2018 at 20:28