I have heard people using OTG cable and a USB cable to charge one mobile from another mobile. I was wondering, Could I use the micro USB port directly to power external devices like LEDs.

I cut up the adapter wire and connected the micro USB in my mobile. The external 2 leads have no output at all.

I searched on the internet to how to turn on the power of the micro USB in mobile. I didn't find any material. I searched app store to find an app that uses a protocol to power on the USB port. But No results

How can I do it?

  • This link might help you- electronics.stackexchange.com/questions/34741/… – Akash Neel Dey EEE Feb 5 '17 at 13:55
  • Note: not all phones/tablets support USB OTG, I knew a small start up that nearly screwed themselves because they didn't realize their chosen control tablet didn't have any OTG capability. Basically there's a little resistor on the 5th pin in the micro USB connector that tells the device if it's supposed to act in HOST or DEVICE mode (I forget what the resistances are), HOST mode is when the phone acts as the host PC and supplies power from it's own battery and DEVICE mode is the normal state when the phone pulls power from an external source and acts like a flash disk or something. – Sam Feb 6 '17 at 1:05
up vote 0 down vote accepted

If one wants to turn a phone/tablet into host mode, the (ID pin) must be grounded. It is done in USB cable, in the overmold. The device-kind of USB cable has this pin floating. Unfortunately, a normal cable does not have this pin exposed, so you need a special "OTG adapter" cable, which has the ID pin grounded. Then you might be able to turn your mobile device into HOST mode, and it will output 5V on VBUS pin (Red wire). You can safely count on having at least 100mA from it, which can lit-up a substantial LED chip.

But I wonder why do you need an external LED when any phone has a built-in one, as a photo flash? There are lots of apps that use it as a flashlight...

  • The Mobile flashlight drains the battery very fast. I was thinking to lit less rated LED for long period of time. – Masood Salik May 30 '17 at 13:05

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