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I have a USB 2.0 signal cable without power. (connects the piano with the tablet).

These are my ports / terminals:

  1. male, USB 2.0, type A (end of piano midi cable, without power, only signal)
  2. female, USB 2.0, type Micro-B (tablet input)

I have a cable connecting both of the above terminals.

Problem: the tablet doesn't charge. I want to add power to this cable so that the tablet will charge while it's connected (and it's almost all the time).

What to buy?
(I combined with various cables and adapters, and the effect is that there is either power or signal)

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  • Maybe a USB3 hub may help? So connect devices to hub and hub to wall. I'm not sure it'd charge as well as directly from the wall.. but it may charge better than from some other device that might not have a USB3 port. Also USB3 cables are cheap
    – barlop
    Apr 21, 2020 at 14:37

2 Answers 2

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I want to add power to this cable so that the tablet will charge while it's connected

I would insert a powered USB-hub between MIDI-keyboard and tablet.

The problem may be that neither the MIDI-keyboard nor tablet consider themselves as host devices responsible for providing power or that the tablet requires more power than the original 5V x 500mA standard provides for - the tablet may be unable to negotiate a higher power.

Check the current or wattage rating of the power-supply (wall-wart) provided by the tablet maker.

The USB 3 standard has specific provision for higher power devices and so, if your tablet is USB 3, it may be beneficial to use a powered USB 3 hub between MIDI-keyboard and tablet. It won't hurt to try.

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  • you write "or that the tablet requires more power than the original 5V x 500mA standard provides for - the tablet may be unable to negotiate a higher power." <-- What if he uses a USB3 powered hub, and USB3 cables and connects his devices to that? He should get better than 500mA for any device requiring more. Though I guess perhaps still limited to 5V.
    – barlop
    Apr 21, 2020 at 14:40
  • @barlop. I agree, good point, assuming the tablet is a USB3 device. Answer updated. Apr 21, 2020 at 14:45
  • Tablet: samsung galaxy tab S (usb 2.0). What do you thing about this hub: USB Unitek Y-3089
    – Geri
    Apr 21, 2020 at 15:01
  • Also if he can connect a device to a hub for power, and he can connect a hub to a wall, then he can connect the device to the wall. Can his tablet really not charge from the wall while having a USB device connected to it? Maybe they all can. (I have a phone that can't easily but a tablet probably can). I have a computer that is a tablet and it has a USB-C connector on it where the power connects to it. And it has a USB-A connector(the rectangle), where a device can connect
    – barlop
    Apr 21, 2020 at 15:06
  • @Geri: I can't make any recommendations, sorry. The mention of BC1.2 and the port for power injection seem promising. Apr 21, 2020 at 15:08
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You are looking for a device (adapter) called "accessory charger adapter". See also this answer. The device/cable has special value of resistor on micro-USB ID pin. It might work assuming your tablet supports the accessory charger mode.

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