BTW @ DrYak, if I have a chance to build a handheld PCBA from scratch, how many open connectors that you need *ideally*? (Give me as many as possible) I think your suggestions are great and I do consider adding them in the future. (Not in the current one)

Hey guys, don't start any distro war

(and everyone knows btw that Fedora is the best desktop distro. Why? Because I'm using it! )

m'distro *tips*

Linux?... Windows ftw!

/me hides

There we have it chenphone
Sounds snappy, honest, personal, dedicated, international and unique.
No prominent search results as of yet.
Hurry up, chenphone.com and the brand is still available

And now that i proposed it, you could always point to this post if someone accuses you to be bigheaded, conceited, arrogant or sporting to much selfesteem when having a product containing your name!
It is just a cool short name with some organic history and possible markting spin.

Or will you go the safe youyota phone route? (not bad either!)

Why limit yourself with just a "phone"? (Especially when he's releasing a Tablet )
Just "Chen" might fit better, although these are probably already taken

Hence the use of expressions such as in my experience and one of the best.
As they say : Your Mileage May Vary.


also, Gentoo rules them all ! :-D

Happy that my comments are somewhat useful / inspiring.

Of course, it depends whom you ask. For somebody deep in the "Makers" community, they'll stop at nothing under a full Arduino's worth of repurposable GPIO pins. :-D

More seriously, I would think :

- the bare minimum would be charge pins (i.e.: ground and a +5V input *TO* the phone) so it would be easy to re-use any of the various wireless charging solutions (Qi receivers are cheap online, other people might still have Palm/HP's magnetic touchstone receivers) or even cobble on weird idea (solar panel ? hand crank ? other bat-**** crazy ideas ?), all this with minimal modifications that are pretty much standard in the market (even lots of big brands provide contacts for aftermarket third party wireless chargers, Qi being the most popular standard).

- at least a simple BUS to communicate with gadget.
Jolla Phone's I2C is a good start :
there are tons of chips supporting it, there are libraries for micro-controller to support it, so it's easy to make a prototype of something for users.
It's already available on most phone as they use a I2C bus for lots of sensors, as far as I know it just requires adding extra contact points on the bus (and require very few connectors - 3 wires are enough).
successful 3rd party aftermarket accessories like "The Other Half - Keyboard" (TOHKBD) have been possible thanks to this.
(and it should be possible to make a back-cover OLED or eInk test-only display using only off the shelf parts).

- and/or some higher speed bus like USB would be even better, enabling high speed accessories (audio over USB, a full graphical back cover display, etc)
Or more standard off-the-shelf component (think USB keyboard controller)
But it's going to be a tiny bit more complicated (extra "hub" chip ? or a SoC that have more available USB lanes ?) and requires 4 wires/contacts (or even more for USB3).
But way much more versatile than I2C enabling lots more accessories.

- another thing that might be worth looking in the future : maybe by the time you start having budget to design own PCB other bus will become standard for phones ?
the project ARA (the attempt to make phones modular like "lego" toys) had designed a bus called "Greybus" (a wink/pun to the Greyhound autobus travelling), that is supposed to be very high-speed and be able to carry quite a lot of different logical information (not only USB but even display).

Power, I2C, USB.

That's for the things that would be nice to have under the battery back-cover, preferably as pogo pins, or at least large contact pads.

(I at least would easily see my self playing around with those, and can imagine the "big pros" in the community crowdfunding aftermarket 3rd party accessories around those)




Then something that might be relevant for a few users :
if the PCB could still have contact pads for JTAG :
that would help the more pro-hacker to "debrick" a device with broken firmware.

And of course, a big row of programmable pins as in raspberry pis (can be assigned to do SPI, I2C, etc.) or in arduinos (fully micro-code programmable, can be used for anything as long as the arduino has enough processing power) is going to make any big hacker salivate.
But might be over kill.

By that point it might be better to 3D print a home made back cover with a built-in arduino, talk with the main smartphone over some more conventional bus (e.g.: USB).
Or some other specialized circuits.


(e.g.: imagine somebody building a back cover with USB chips to receive/emit walkie/talkie radio, so a group of friends doing outdoor sports can still contact each-other when outside of cell coverage).

3 wires are not enough. You need at least 5 wires: 3V3, GND, MISO, MOSI, CLK.

I think that's one of the forms of SPI that you are thinking of. IIC requires only SCL, SDA and GND (being open collector signalling), but a 3v3 or 5v0 output is useful also.

Add to that an unregulated 5V input for charging, and my wish list would be complete. (By unregulated, I mean apply 5V +/- 0.?V capable of delivering ?A and the device takes care of charging management)

Oh, and I like 'Chensphone' as a name better than 'chenphone'