OTG - USB On-The-Go. My experience

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This is my experience in using a USB OTG between a phone and SD card reader.
I wanted a simple way for my wife to transfer camera pics (SD card) to phone for social media while she was on holiday.
I purchased a Micro USB to Micro USB OTG Cable - 10 / 25mm SKU: ADA3610. It would connect between the phone and a USB Card reader we had. But it did not work.
I then purchased a cable similar to Micro USB OTG Host Cable (for Raspberry Pi Zero) SKU: CE04761 and a card reader with a standard USB connector and it worked perfectly as OTG.
This got me wondering why the original cable did not work. In my investigation I found that pin 4 ID pin of the micro USB connector must be GND for the phone to switch to host mode and read the SD card. The first cable has no connection to pin 4; the second cable did.
When you think about it, the micro USB to mico USB cable could not have pin 4 to GND for both ends. Both devices would try to be host. If only 1 end was GND, it would need a label, which may come off … etc etc etc.
The other cable is perfect for OTG as it can only be connected one way.

I relate this here in the hope that someone else may benefit from my experience. The google information I found did not explain specifically the connection of pin 4 to GND causes the phone to switch to host mode.

Core Electronics should add a note to the Adafruit description of the cable to state that pin 4 is not connected to GND. The cable can be used in certain situations to connect two USB micro devices but not when it is required to switch a phone or tablet to host mode (OTG). It is not the right cable to do this.

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Thanks James!

I will pass this along to our webmaster! Thanks for the feedback!

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Further to my previous post.
I have absolutely proved the cable, Micro USB to Micro USB OTG Cable - 10 / 25mm SKU: ADA3610, will never work as an OTG cable. pin 4 ID is not connected to anything and not carried through the cable.
Adafruit should remove the reference to OTG on their web page. I sent this information to them and they responded by asking for a pic of what I had purchased. The cable works perfectly if you connect a micro USB to micro USB device but will not switch a phone or tablet to host mode (OTG). It is not the cable that is the problem, it is their description of the cable.
I used two USB Micro-B Breakout Board SKU: ADA1833 and a multi-meter to prove the lack of connection on this cable and the connection of pin 4 to GND on the other cable I purchased. The breakout board allows easy access to the pins.
I post this here in the hope that it will save someone else the cost of buying a cable that does not do what it is advertised to do.

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