Android Question Serial Port Access on Motorola Droid RAZR Maxx in USB-OTG Mode


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First of all - my complements to the B4A team for a very nice piece of software! Well worth the money!

I have successfully tried the UsbSerial2.3 library example program on my Motorola MZ617 10.1" tablet, Android version 4.0.4. Using a standard USB-OTG cable, it works fine communicating with a FTDI-based serial converter. On thing I notice is that the host immediately acknowledges the device as soon as its plugged into the USB port, as I can see the internal comm LEDs blinking for a few seconds. I assume its being mounted by the OS during this period. All is good ...

However, I've been "down the rabbit hole" today attempting to get the library example working on my Motorola Droid Razr Maxx (Android version 4.1.2). Turns out that on the RAZR Maxx, the OTG port must be externally powered using a Y-cable and an 5V external supply or powered USB hub. After hours of scouring the forums, it looks like the RAZR will not even acknowledge the device if there is not enough current present on the buss to support charging. I can kinda understand this limitation, as USB peripherals would drain the phone's battery very quickly...

Anyway, I've got all of this covered, but I still have no luck accessing the port. Upon "starting" a connection, I get an Android dialog box with lots of information about the USB port, and it clearly states "Serial: Not Installed" right near the top of the screen. On the MZ617, this same dialog box appears with a reference to the FTDI chipset.

So, I am guessing that there is some driver that is not installed on enabled in the OTA version of the OS distributed by Motorola. I was hoping that someone on the forum has run into this same issue and knows of a solution.

Thanks very much,