FP2 back connector and FT311 (FP2 back connector is stuck in host mode)

Thanks, good to hear! :smiley:

Ehh yeah sorry this is going to be impossible. The backconnector is stuck in hostmode and thus the ft311d cannot be used (since it is in hostmode to provide accessoiries for non-usb-otg phones). So I am sorry to bring you the bad news, but you can expect to never see fp2 smartcovers.


In your bad news maybe you missed to refer to the FT201 that I also get. Also bad news for this ?
Or better some hints what software is needed with android ?
Let’s have again a look on your advice for TOH adapting to FP2 (!)

So, I made my order with both FT311d and FT201 (tiny) breakouts according to your schematic above.
Did you include FT311 on the sketch to simply connect it by a USB patch cable downside to the FP2 ?
So, why shouldn’t I simply follow your plan ? You gave advice to use both FTDI’s alternatively , didn’t you ?

I also have a Jolla-phone wich maybe usefull to turn the FT311 for use as an OTG there ? Any ideas ?
I got all FTDI breakouts from holland (bitwizard) , I got my smartcovers from holland, FP is from holland - so it cannot be all wrong coming from NL :wink:

sorry , this I didn’t get it because I already have your FP2 smartcovers on my table here (?)

well, good luck writing your own android drivers for it

yeah that has not been updated for a while. i had high hopes before that all was possible.[quote=“anon9505190, post:45, topic:11614”]
I also have a Jolla-phone wich maybe usefull to turn the FT311 for use as an OTG there ? Any ideas ?

You’ll be able to use the ft311d for any phone’s micro usb port on the outside (including the one on the fp2 but not the backconnector)) regardless of whether it has usbotg or not to make accessoiries. Just provide power from outside source and use android ft311d drivers

that is physically impossible. cover maybe, smartcover not so much

sorry for confusion, after learning first time about smart covers I am still not sure why you mention it here (that’s why I got confused) Maybe because you abandoned any kind of I2C on any FP2 . Of course without SDK and some driver software this kind of hardware extension will not work out of the box . But this was clear from the first look on your scheme. However the FT311 with FP2 front USB client still is first choice for testing.

sure, but controlling the ft311 over the backconnector is impossible. not now, not ever.

the ft311 was the perfect candidate, since there are already android driver for it. however, it is a host chip and the backconnector is stuck in host also. so: impossible to use.

Why not talk about FTDI’s vinculum-II/VNC2 ? Unfortunately it has SPI instead of I2C only, but the toolchain is quite open including examples apps for android ? As far as I see the roles between USB host&client is open in both ways

Yeah also a good option, but without any documentations on the phone side i am not going to risk burning a lot of money again to find the next hardware or software restriction.

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Chapter 6, page 9 .

The Open-Accessory-Mode is better documented than e.g. with FT311

Indeed I never saw better and complete documentation for android development with microcontrollers
That is why you recommended FTDI already long time ago. I followed your advice and found the same docu.
I am not sure what you mean now by saying … without any documentation on the phone side

Just another example :
VNC2 Android Open Accessory to USB Bridge Example 4th July 2014
FTDI have released a Vinculum II source code project to compliment the FT311/FT312 USB to UART, SPI, I2C, PWM, GPIO solutions. This example describes how to use the Vinculum II (VNC2) to host an Android Open Accessory USB port and bridge to another USB peripheral e,g, the FT232. The user can take this starter project to get started with their own specific application and add USB accessories to their Android platform.


The devices that attach to a phone using things like Open-Accessory-Mode provide a nice workaround for phones that do not support HOST or OTG mode. When operating in such a way the phone can not properly suspend (being the “slave” of the attached gadget.

Using usb host on the back connector was/is the right thing to do.


Hi Kees,
Your answer is appreciated because I am working now with all equipment including my FT311 for making a NFC device possible. However the software inside the phone will be still a challenge. (Because I still have to prepare my android SDK including complete VM simulator …)

Today I received my second battery from FP. I already have the case with the “hunchback” that fits exactly for the battery. My question for the expert today: Can I just connect 4 battery contacts in parallel e.g. by little tinfoil stripes without further semiconductor elements ? Will I double my power supply with the second battery this way as simple as I think without any risk ?


I still should be possible to connect the FT311 chip to the “normal” OTG port but no power will be delivered to the peripheral. I would recommend using a different approach.

The second question you have is about the development environment. I don’t think the android emulator has support for usb devices so running your code inside an emulator is probably not the thing to do. Just install android studio and connect to your device using adb over a wireless connection.

(I previously looked into usb support of the emulator but this was a few years ago https://github.com/keesj/gomo/wiki/AndroidEmulator )

If you are a c/c++ coder and you are using a usb device you can also develop 95% of your driver under Linux/windows using libusb and move to the android libusb later.

With regards to batteries…
It does not look like the recommended way of doing things. https://www.reddit.com/r/AskElectronics/comments/1p0uiw/asking_for_clarification_on_wiring_cell_phone/

thanks , I got it.I Should have known better before. I hoped hints for a balancer would still make s.th. still possible. But, …( never mind … )

I thought about taking power from the internal USB connector (?)
But yes, you’re together with Dirk on the right side when FT201 with internal USB host is the better (and cheaper) approach. But not for point of view from the software. Maybe I was not too clear about only starting with FTDI chips that has complete android driver software ready to use. Maybe you or Dirk only missed the point of my approach of FTDI2 VNC2 : this chip doesnot need the usb slave access but also needs power given from the internal usb host.

My qemu emulator actually has usb support and even your example already have had it. ( you left me a bit puzzled) . Recommending to use my productive FP2 as the testing and qualifying device extended a bit the puzzles in my head. You may have seen I am not that expert as you definetly are. Using qemu emulator for staging to me still looks mandatory. Just let me give it a try.

Do you see any reason why the same with required PCM modules for protection on each battery cell should not have any risk any more ?
Openly spoken I don’t understand why there is still no makers advice how to double FP2 power when everybody could complain about the weak FP2 battery power ? The oftenly recommended power banks are an option but they are not the same as a real extended battery pack. I think it is missing here.

Hello Kees,
For battery extension I need an information from your side.
The FP2 battery pinout is only documented with + and - pins.
What is the pinout for the 2 other pins in between + and - on every FP2 battery ?

thanks in forwards