Fairphone 2 hardware extensions

Hmm, dismantled the phone, but I need to go a level deeper to access the back of the mainboard. How easy is that last part? I ran out of time.

2 min :grin:

At least that is what they claim :wink:

You’ll need a small torx screwdriver.

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I don’t mean to spam this forum… I am interested in getting a response to my questions regarding building internal hardware for the Fairphone 2. Should I ask these questions elsewhere?

Thanks for you help.

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What questions you need answered???[quote=“YileKu, post:52, topic:11457”]
I want to know if the specs for the network interface are open or if there is a USB hub in the phone that is accessible.
Not that I know of, we’ll have to wait for official dev kit

I dont know what you mean here.

Also, don’t get what you mean

No. Wait for official dev kit.

7 posts were split to a new topic: Fairphone 2: Photos of the components around the charge input

Do these links help?


That repo by @keesj is cool, I love that USB breakout for the yubikey :slightly_smiling:

@dvl’s work featured heavily in @keesj’s FOSDEM Talk, great to see Fairphone support their community like that

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Finally had time to do some measuring. All Bat-Voltages are taken by removing the bat from the phone.

Case a)
-No Charger connected
-Battery Voltage at 4.12V
-Phone turned on

Charge is at 0V
VBUS is at 3.90V

Case b)
-Charger (Laptop)
-Battery @ approx 4.1V
-Phone is “off”

Charge pin @ 0V
VBUS pin @ 3.99V

Case c)
-Charger (Laptop)
-Battery @ approx 4.1V
-Phone is “off”

Charge pin @ 0V
VBUS pin @ 3.94V

Case d)
-Bat fully charged (says Phone) @ 4.31V
-Almost no difference if FP is on/off and charger is dis-/connected

VBUS @ 4.12V

My personal understanding of this is, that there is a Schottky diode (or something similar) between VBUS and Bat+ => You can not charge via VBUS, you won’t get higher Voltages than ~4.15V.
Charge is always at 0V. With a conductivity test I get a reading of about 1.4V for the voltage drop between the Charge-pin and Bat+. This lets me believe, that there is some kind of regulator in between.

Surprisingly I got an almost perfect conductivity test between (GND)->(VBUS). This might be some kind of protection against wrong polarisation? But that would fry the PCB if enough power was connected, right? Nothing like that between (GND) and (Charge).

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Bit quite from my side, was chilling on ther beach in Chile, but had some time to make some fluffy text to fill my github.

Should go online sooooon. Lots of incomplete infos btw, just so you guys and gals know.



VBUS is conected to the PMIC’s charge pump (the same one delivering 5V when using USB OTG). It is not possible to charge via that pin.

The charge pin allows charging it is connected to the secondary charge pin(DC_IN) of the 8941 PMIC.

Thanks keesj!
I could not get 5V on that pin, even if drawing power. Do I have to connect a usb device to negotiate a protocol first? Is there a possibility to draw 5V from that pin without usb controller? Is it okay to draw power from that pin without having a usb connection negotiated? What is the maximum rating either way?

Btw: is there a datasheet for that chip? I could not find one…


Thanks for the files. I am going through them. Is there a general overview of how extension modules go into the fairphone? I will need to convert the CAD files to SolidEdge to get a better look.


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Still working on this myself :slight_smile:

This is generally done with the series resistors on the data lines, look into that

Hello Aypac,

5V will be delivered to the pin with or without USB enumeration. There is, of course, a datasheet for the PMiC but it is not freely available. if you are running the official 1.1.7 release the port is not yet supported you typically will only get 3.2 volt on the power pin and, among other things like the USB phy will not properly be powered.


OK. Thanks to another thread, I have also connected an USB keyboard to my Fairphone 2. That also works.

Oops! In the linked thread, the thread opener asks about Fairphone 1. So I didn’t answer him.


Dear @TobiasF,

Thank you for your response!

Since you talk about the FP2, do you think the FP1 will work with an external USB keyboard, too?



Hello !
Thanks for sharing this picture @TobiasF. Very cool easter wishes sending setup :slight_smile: :slight_smile:

About USB device compatibility, did you have a look over this FP2 thread ?

@orschiro I don’t own an FP1, but I would encourage you FP-Oners to grab an OTG cable (around 5€ on the web) and test for yourself, and why not creating a similar thread.