Unable to connect a TTL to USB converter to a phone

Question

I have been unable to connect the USB side of a TTL-to-USB converter to a phone by using a Female-Female USB A adapter and a normal mobile phone cable (which can handle data).

This is the converter being used

The TTL-to-USB converter has been successfully tested with the phone in the past by using one of these connectors.

This is the diagram of what I am trying to achieve however for some reason with this setup, it does not work.

Any help would be greatly appreciated.

Answer 1

USB is not an equal peer-to-peer connection; it was designed with one device acting as the "host" (supplying power, assigning addresses, etc.) Normally the type-A connector always goes into the host and type-B connector goes into the "slave" device.

USB micro-B connectors have an additional pin indicating OTG (host) mode vs regular (device) mode. Actual "USB On-The-Go" adapters have this pin grounded, indicating to the phone that it needs to reverse the port's operation (switch to USB host mode and provide power, as opposed to receiving power).

Your "normal" cable does not connect this pin, because after all it was made to be used in normal mode (with the type-A end going into the USB host instead). So the connection has no device acting as the host.

The female-female type-A adapter cannot do this on its own, because type-A connectors predate USB OTG and do not have this pin (i.e. it doesn't even go all the way through the cable, it just loops back inside the type-B connector).

(Type-C is even more complex, I don't know anything about how it decides between modes.)